Current PDF Edition - Broadcast Dialogue

Engineering 101:
Dan Roach’s 101
Broadcast Dialogue
columns
For more than 10 years, the brilliance and down-to-earth presentations
by Dan Roach have graced these pages.
Now, as a special supplement for those who may have missed saving
and filing away each and every one of those columns, Broadcast Dialogue
has put together the Dan Roach collection—easy to use, easy to access,
easy to read and, importantly, chock-a-block full of his broadcast engineering
expertise, his wit and, occasionally, a certain amount of his charm.
Roach’s broadcast career began in 1976 as an announcer. Later he
became a newsman and, still later, he found his niche as a broadcast
engineer. Dan worked in such markets as Burns
Lake, Smithers, Prince George, Kamloops and
Vancouver. With typical tongue-in-cheek
humour, he quickly discovered that
“announcing was not a job for
grown-ups.” And as a newsman,
he said, he made “a pretty good
engineer.”
The northern B.C. stations
where he began were owned by
Ron East and Stan Davis. Davis
also owned BTS (Broadcast
Technical Services) where
Roach eventually ended up.
Upon Davis’s passing, Dan Roach
became the principal at BTS and
still maintains that responsibility.
From his first column to the
most recent, all of his thoughts
and advice on broadcast engineering
stand the test of time.
Enjoy the Dan Roach collection,
compliments of Broadcast
Dialogue.
Click here to
download the book
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • May 16, 2013

Table
of contents
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
Arc flash, and other NAB news
The road ahead
Transmission lines down through the ages
Estimating maximum power
Two months in, do you feel CALMer?
This ’n’ that
MDCL – Worth a second look?
A high voltage repair survival guide
Try to remain CALM*: Is this the end of the loudness war?
NAB 2012: Is that change that I smell?
Worms from the can: Audio pre-emphasis run amok!
AES/EBU: The battled rejoined
Ones and zeroes can take many forms
Of gain and squint and tilt (Oh, my!)
Ramblings about radio – past, present and ... future?
Techno-quacks on the march
The capacitor plague
Through the looking glass: NAB Las Vegas 2011
AM dynamic carrier control? A true story!
We all could use a good belt now and then…
Stuff to do before something breaks
Sins of the past revisited: RDBS best practices
DRM plus: for us?
…and thus the whirligig of time brings revenge
RF dentistry: Filling your cavity’s needs for repair
Reflections on standing waves
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • May 16, 2013

Table
of contents
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
Engineering notes from NAB 2010
I remember the CAB technical committee
Monitoring surround sound for broadcast, part 2
Monitoring surround sound audio for broadcast
Form C Contacts: Very dry, shaken, not stirred
Tag, you’re it!
Grrr!! Attack of the angry engineer!
A cure for voltaic piles rediscovered!
The air is humid; to be cool, divine!
Ruminating on the DTV rollout
Random thoughts from NAB 2009
Circuit breakers, power factor and back e.m.f:
Things your mama never taught you
Serial interface survival guide
Confessions of a serial interface killer
Blast those transmitter varmints!
Bring me your lemons
The wonderful world of wire
It’s giant leap of faith time again
Pre-processing audio for digital
I, Bach returns!
Extra! Extra! More broadcast features for you!
Audio monitoring in the control room
Acoustics and monitoring, Part Two
Acoustics and monitoring
Strange radio stories of yore
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • May 16, 2013

Table
of contents
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
It’s AES/EBU for you!
Just looking for trouble, Part 3
Bulletproofing your site, Part 2
Thinking the unthinkable: Disaster-proofing your plant
Loads of fun with quarter-wave sections and pads
History of broadcast audio processing
Daring Dolby tackles TV loudness
Fable of a farad
Batten down the hatches, winter’s on the way!
I, Bach! U.S. broadcasters try reinventing radio
Remote controls we have known
NAB has come and gone… (do dah, do dah)
When is new not better?
The many flavours of surround sound
Searching for the right level
Be careful what you wish for
Stop this paradigm shift, I wanna get off!
Reg Fessenden clears his throat
Alphabet soup for breakfast
Admitting your susceptance to my resistance
to impedance
String, tacks and sealing wax: AM transmitters
of the future
RDBS in your future?
Gibbled audio in the digital domain!
More on quartz
Nazis sank my crystals!
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • May 16, 2013

Table
of contents
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
Fixing the stubborn switcher, Part II
Switch-hitting your power supply
Mysteries of the shielded loop revealed!
Rogers to the rescue
Further reflections on multipath
The story of Conelrad
Depolarizing a polarized world
The marginal path: FM radio and the real world
Look up in the sky! It’s a bird! It’s a plane! It’s a yagi!
Yagi, Yada Yada Yada
Fighting the urge to surge
Lightning, grounds and other accidents of nature
Practising transmitter safety
Safety Code One or diatribe about danger
Perils of the dog biscuit
Many flavours of dog biscuits
Eeek! It’s Safety Code Six!
The history of broadcast engineering: Chapter CCCXLIV
The wisdom of the ages!
Further adventures with Ma Bell
Resistance is futile – but impedance is
(sometimes) important
How stuff breaks
Radio redux – tales of errant gensets
A safety primer for transmitter visitors
Radio redux—whither tomorrow’s broadcast engineer?
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • May 16, 2013

Coverage
Arc flash, and other NAB news
by Dan Roach
Time to recap some of the more important news from NAB. A tip of the
cap this month to Jeff Welton of Nautel who regaled us with the potential
horrors of arc flash. Although this has apparently been simmering in
the background for some time, it is information that every technician working
at a transmitter or studio plant should have. I confess that I had not heard of
the expression arc flash before Jeff brought it up. I encourage everyone to do
a little research on this subject.
It could save your life!
Arc flash can occur when electrical contacts or conductors carrying power
above 208V and 125kVA (this would include all high-power transmitter sites and
many studios) choose to arc over. The resulting arc, even if allowed to carry on
for only a few cycles before it is extinguished, produces a high-energy plasma
with temperatures as high as four times that of the surface of the sun (i.e.
arc flash at 20,000 degrees C). There are two dangerous consequences, with
the unsettling names of arc blast and arc flash. The rapidly expanding plasma
causes contacts and switchgear and covers to fragment and explode as hot
shrapnel—that’s the arc blast. The intense radiation from the arc, including
infrared and UV and everything in-between, can cause severe burns even if
there is no physical contact; that’s the arc flash.
The natural first reaction is to make sure that circuits are powered down
before any work is undertaken. However, it’s important to realize that the
switching involved in de-energizing equipment can actually increase the risk
of an arc flash. Also, none of this takes away from, but rather adds a new dimension
to, all the electrocution hazards we have discussed in this space in
the past.
This is a pretty broad subject, and there’s much more than we can go into
in this space. There are U.S. and CSA standards out there and all sorts of
safety equipment available. But here’s what I took out of all this, at a first
go-round:
• Learn from the example of every electrician you’ve ever watched, and stand
beside, not directly in front of, the safety switch when you’re going to
throw it. Have you ever talked to an electrician that has never had a panel
explode in front of him? Neither have I.
• Any electrical equipment that could potentially flash over, especially switchgear,
should have an arc flash warning sticker on the front of it.
• Realize that under the rules, even to just remove a switch cover exposing
live contacts above 208V and 125kVA, you should be wearing protective
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • April 25, 2013

headgear and clothing. Take a look at the protective gear being sold by
the electrical vendors. You’ll think you’re outfitted for a trip to Three
Mile Island! Better yet, get an electrician to do it for you. This was
true before, it’s even truer now!
And in other news…
Like at every other NAB convention, the exhibitors are often trying to
make the case that there’s actually something so new and so revolutionary
that you’ve just got to have it to carry on, and preferably today if not
sooner. Working against this is the fact that new trends in broadcasting
equipment tend to be evolutionary and don’t often just materialize overnight.
So, as one wag put it, we see a lot of last year’s stuff but with a new
coat of paint on it (probably in some hideous day-glo colour).
If there was a theme to this year’s show, it was the dance of the “Ks.”
Forget ATSC, we were inundated with 2K, 4K, 8K and perhaps even a little
16K video. Mostly these were being touted as production standards, which
strikes me as just fine, but there were still some trying to reinvent transmission
standards to broadcast these signals, and the ATSC2 and ATSC3
people were out there too. 3D video also refused to die. C’mon folks,
there’s no spectrum available for this and little appetite from broadcasters
or consumers to make everything new obsolete before its time.
Perhaps the biggest surprise is just how inexpensive a lot of very highend
video equipment can be. There seems to be a whole sub-industry
developing of makers of cameras and processing equipment that, while
compromising a bit here and there, can produce cinema-quality video
for a couple of kilobucks or less. (However, the careful observer may
note that there was often $30K worth of lenses attached to that kilobuck
camera).
The amount of value per dollar implied in the GoPro Hero ruggedized
miniature cameras and many of the high end toys produced by BlackMagic
Design underscores my point. A couple of years ago, the breakthrough Red
cinema cameras were the talk of the show. This year they had company as
other clever manufacturers strove to demonstrate just how far you could
go with a few bucks.
Click the button
for more information.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • April 25, 2013

For those of you who have been following
this diatribe as it wends its way, inexorably,
over and around and through the broadcast
engineering business, this is my 100th column for
Broadcast Dialogue. Through the years we’ve
often talked about the way things used to be and
the way they are today. Perhaps this is a good
opportunity for some navel-gazing about the way
things are likely to be in the future.
That’s a pretty tall order for me. I often find the
crystal-balling of many of the pundits to be kind
of unrealistic if they’re creative and self-evident to
all if they are not. Maybe a lack of vision or short-
The road
ahead
by Dan Roach

As broadcasters
increasingly
embrace PCs for,
well, everything,
they’d be welladvised
to keep
in mind that PCs,
while surprisingly
affordable, remain
a consumer
product with an
estimated life
of three to five
years before
replacement.
© Dawn Hudson | Dreamstime Stock Photos
sightedness on my part; perhaps. But we’ve seen so many
“next big things” come and go, or never come around at all,
that I maintain a certain healthy scepticism is essential; DAB,
AM stereo, r-DAT, elCasset, minidiscs, Dolby FM and quadraphonic
sound to name a few.
At the risk of offending any true believers, perhaps HD
radio as well.
Meanwhile, while we prattle on about what’s to come, our
whole infrastructure and way of doing business is (not so quietly)
turning itself inside out in innumerable small ways, most
of which we didn’t anticipate (pass me the floppy disk!).
The trick in my view is not to just to see the trends in new
technology but to make the vital connection as to how they
will affect the tides in our lives in years to come. Just as the
transistor is finally stamping out the power tube (it’s only
taken 60 years or so), the LED is pushing hard to eliminate
tungsten and the solid-state laser led inevitably to the CD
and DVD.
I guess once the CCD came into existence the writing was
on the wall for the Plumbicon.
Broadcasting and the professional audio/visual industries
are increasingly being tugged on by the consumer electronics
industry. And while that’s giving us a pretty exciting ride
with new technologies and affordable new toys, it sometimes
causes alarming instability.
When the first big SCSI drives came out in the 1990s,
radio stations seized upon them as an ideal way of affordably
storing digital audio. Of course, those giant eight Gig hard
drives (gasp!) weren’t made specifically for audio, nor in fact
for any application that requires a constant stream of data
retrieval.
Who amongst us remembers the horrible fact of thermal
recalibration as the drives hesitated every once in a while to
tune themselves up in the middle of retrieving an audio file?
A couple of columns ago we were talking about how
changes in the wireless industry have led to difficulties in
getting certain types of transmission lines and RF connectors
for broadcast. Earlier, major transmission line makers Andrew
and RFS Cablewave stopped making rigid transmission lines
broadcasters depend upon. These events were caused by the
growth and changing tastes of wireless.
Could we have anticipated them?
Broadcasters beware: Consumer electronics, and the
wireless industry by extension, are not really interested in
our needs and they will take no prisoners as they continue
to advance and push the technical envelope searching for
untapped markets. They care little for the wants and desires
of broadcast operators or the attendant expense to us
of changes in technology or standards. ATSC was accepted
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • March 21, 2013

surprisingly quickly once the signals became available but home
A/V has hardly stopped at 1080i and 5.1 surround sound, and there
will be increasing pressure to keep up.
As broadcasters increasingly embrace PCs for, well, everything,
they’d be well-advised to keep in mind that PCs, while surprisingly
affordable, remain a consumer product with an estimated life of
three to five years before replacement. And the computer you buy
next year will not be terribly compatible with the one you bought
this year, neither in hardware nor software.
Welcome to the wonderful world of personal computers!
This, of course, is affecting all sorts of businesses but that
doesn’t make it any less true: I recently heard the author of the
LemonAid series of used car buying guides bemoaning the fact
that today’s motor vehicles increasingly use microprocessors for
controlling everything because it allows them to economize and
add new features at the same time. He warns of depressed resale
values for these vehicles as their onboard computers increasingly
start breaking, with no affordable compatible replacement parts
available in the future.
In the meantime, enjoy the ride!
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a
contract engineering firm based in Vancouver. If you have a question or
comment, contact him at dan@broadcasttechnical.com.
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • March 21, 2013

Transmission lines down
through the ages
ENG
INE
ERI
NG
Last time we were going through some of the calculations necessary
to predict the power handling limits of different transmission lines
for broadcasting. Transmission lines themselves have undergone a
number of generations of change since broadcasting began.
Here’s a short version of how we got to this point:
Originally, high power transmission lines were invariably open-wire
style, running at fairly high impedances, for instance 230 ohms. The transmission
lines used a lot of power-line technology so far as power poles
and hardware were concerned. Poles had to be placed fairly frequently to
keep the spacing between the inner and outer conductors consistent.
Power handling capability was high and losses were low but, even so,
a light breeze could change the impedance of the line pretty drastically.
Early coaxial lines started to appear in the 1940s but they were still mostly
a curiosity: they were available up to about 1-5/8", were pressurized and
unjacketed (no direct burial allowed) and impedances were fairly arbitrary
(about 65 ohms in one example).
As FM and TV installations became more frequent, the need for higher
powers and higher frequencies became apparent and larger gauge lines
came onto the market. By the 1960s, air lines up to 5" were available, and
open wire lines for regular broadcast had become obsolescent although
there are still a very few of them to be found in these parts to this day
(and they still have a place in high-power shortwave installations).
Impedances were standardized at about 50 (and very occasionally) 75
ohms. Lines started being supplied with a jacket so it became possible to
bury them at AM sites thus saving on installation and maintenance costs.
The development of foam-dielectric lines up to 3" has followed the air
lines. Market acceptance was rapid in the smaller sizes as the fuss and
cost overhead of air lines (dehydrators and pressure regulators, manifolds,
air-tight connections) was effectively bypassed, along with a (somewhat)
lower price. Early production problems with the larger foam lines were
identified and overcome.
Still, as late as the 1970s, if you were trying to install a high-power
UHF-TV transmitter site, you’d probably be using a great big expensive rigid
transmission line of perhaps 9" diameter—by necessity, not by choice!
The extremely large sizes of air line didn’t make an appearance until
the early 1980s. Rigid transmission line has always offered an extremely
good uniformity of product and power-handling specification, especially at
by Dan Roach
Click the button
for more information.
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • February 7, 2013

high frequencies. However, it’s very expensive, it’s very heavy, it’s labourintensive
to fit and install and it doesn’t handle temperature cycling very
well (this is an issue for outdoor use, where a rigid line might go several
hundred feet up a tower. Expansion and contraction of the line with temperature
causes friction and rubbing—and wear—of the inner conductor
at each flange).
Finally, the uniform length of each section of a long line (typically
20 feet or so) causes a small discontinuity that repeats uniformly. This
degrades VSWR performance of the line, a little or a lot depending upon
the care of assembly. Once bigger air lines for this application came along
they were welcomed with open arms.
In today’s world, perhaps 90% of the transmission lines made are consumed
by the wireless/cellular radio industry. This has already had an effect
on which products are available to broadcasters. Wireless repeaters
use foam lines. Nowadays broadcasters often find that these are the only
lines they can get; certainly the only lines that are stocked.
Rigid transmission lines aren’t used much by any group except broadcasters
and, as a consequence, the larger companies no longer manufacture
them. They are still being made by a few smaller manufacturers,
thankfully.
Again, as technology progresses, we see that the wireless industry is
rapidly moving away from the use of transmission line products except as
short jumpers and increasingly using fibre optic cable on towers.
What this will mean about the availability of familiar transmission line
products to broadcasters remains to be seen.
AVCCAM
AG-AC90
Camcorder
LEARN MORE
Click the button
for more information.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
BROADCAST DIALOGUE WEEKLY BRIEFING — Essential Reading • February 7, 2013

Estimating maximum power
Trying to work out a reasonable estimate of maximum power-handling
characteristics for RF connectors and transmission lines for a given
project can sometimes be a real pain. Today we’ll discuss some of
the factors that you’ll want to take into account. When working out safety
margins, it always comes down to the available dollars otherwise we’d
always just overspecify everything and we’d sleep well!
Transmission line catalogues will generally specify a peak power capability
and an average power capability. Peak power limit is related to the
breakdown voltage of the insulation between the inner and outer conductor,
and is a static value independent of frequency of operation. Average
power limits are caused by heating of the line and, so, you’re generally
presented with a table of frequencies and power-handling capability. Because
of the skin effect, higher frequencies heat the inner conductor
more and once it reaches a certain temperature the average power limit
has been reached.
ENG
INE
ERI
NG
by Dan Roach
Other Factors
Well, that just looks too easy, doesn’t it? Look up two values for our
line and we’re done!
In the real world, we also must consider, well, the real world:
• Peak power rating assumes a VSWR of 1, standard atmospheric pressure
and low humidity. Peak power rating decreases with altitude unless
the line is pressurized. Foam dielectric cables often have higher
peak power ratings than air lines but in actual practice the ends of
the line will have air spacing where the connectors are installed so,
generally, these cables will have the same breakdown voltage as air
lines. Allowance for non-ideal VSWR eats up your safety margin in a
hurry. And if it’s an AM installation, you obviously have to take the
positive peaks into account as, at 100% mod you’re dealing with 4x
the unmodulated power—but nowadays who stops at 100%? Another
safety margin gobbler!
• Average power rating assumes calm air at 40 degrees C, no direct
heating from the sun, dry air or nitrogen for air lines and standard atmospheric
pressure and, of course, a VSWR of 1. If the sun’s rays can
hit and heat the line, if the line is buried in soil instead of surrounded
by cooling air or if the load is non-ideal, derating is necessary to some
degree. There are charts available from the transmission line makers
that help with these calculations.
Just as an aside at this point, it’s interesting to note that a couple of
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • December 2012/January 2013 61

specifications that we generally regard as constants…aren’t! The capacitance
between inner and outer conductors of a line does not change with frequency
but because of skin effect the resistance of the inner conductor rises with
frequency and this also affects the inductance of the cable. As a result the
characteristic impedance decreases with frequency. The published figure is
usually measured at about 200 MHz. And propagation velocity decreases with
frequency; delay increases. Again, the published figure is generally measured
at about 200 MHz.
... And Connectors?
So much for the transmission line—now what about the connectors at each
end? If you’re dealing with an EIA flange connection you can generally consider
the connector to be an extension of a line of the same gauge and calculate accordingly.
You might want to tread carefully here, however, as different manufacturers
(particularly the European ones) will give quite different specifications
for the same gauge of cable. Here’s a specific example: a 1 5/8" EIA flange connection
for an FM antenna from a European manufacturer may be rated slightly
over 15 kW average power but you’ll be hard-pressed to locate a 1 5/8" transmission
line to connect to it (in North America) that’s rated more than about 14.4
kW at 100 MHz! (Even if you’re successful, you’re probably not allowing enough
safety margin!)
The same caveat applies to other connectors that don’t match standard
transmission line sizes. How much power can you safely run through an N-
connector? According to Amphenol, about 850 watts at 100 MHz. According
to Huber and Suhner (a European connector-maker), about 2200 watts at 1.0
VSWR, decreasing to 1800 watts at 1.2. Southwest Microwave (a premium North
American connector-maker) allows 1900 watts. Dow-Key makes an RF relay with
N connectors that is rated (by them) at about 2500 watts. You’ll probably have
trouble finding connectors that will match it!
Click the button
for more information.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact him at
dan@broadcasttechnical.com.
To share this article, find the link at
http://www.broadcastdialogue.com/stories.aspx
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • December 2012/January 2013 62

Two months in,
do you feel CALMer?
ENG
INE
ERI
NG
Since Labour Day, the new loudness control legislation has been in
effect. Have you noticed any difference in the comparative loudness
of different program elements on your favourite TV channel?
I didn’t think so.
Neither have I.
Now we know that the appropriate measures to get this job done are
available on the marketplace—from many different manufacturers, and
in a variety of flavours. So that must mean either that they haven’t been
deployed yet, they aren’t working properly or that further adjustment is
required.
Apparently we’re not quite there yet.
by Dan Roach
And, On The Lighter Side
This month, I thought we’d play hooky and enjoy a little engineering
humour. The source: the Internet, of course!
The Top Nine Things Engineering School didn’t teach…
• There are at least 10 types of capacitors.
• Theory tells you how a circuit works, not why it does not work.
• Not everything works according to the specifications in the operation
manual.
• Anything practical you learn will be obsolete before you use it, except
the complex math, which you will never use.
• Always try to fix the hardware with software.
• Engineering is like having an 8 a.m. class and a late afternoon lab
every day for the rest of your life.
• Overtime pay? What overtime pay?
• Managers, not engineers, rule the world.
• If you like junk food, caffeine and all-nighters, go into software.
While The Nine Best Tools of All Time are meant primarily for motorcycle
mechanics; the parallels to broadcast engineering are astounding!...
• Duct tape: Not just a tool, a veritable Swiss Army knife in stickum
and plastic. It’s safety wire, body material, radiator hose, upholstery,
insulation, tow rope, and more in one easy-to-carry package. Sure,
there’s a prejudice surrounding duct tape in concourse competitions,
but in the real world everything from Le Mans-winning Porsches to
Atlas rockets uses it by the yard. The only thing that can get you out
of more scrapes is a quarter and a phone booth.
Click the button
for more information.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • November 2012 22

• Vice-grips: Equally adept as a wrench, hammer, pliers, baling wire twister,
breaker-off of frozen bolts and wiggle-it-till-it-falls off tool. The heavy artillery
of your toolbox, vice grips are the only tool designed expressly to fix
things screwed up beyond repair.
• Spray lubricants: A considerably cheaper alternative to new doors, alternators,
and other squeaky items. Slicker than pig phlegm. Repeated soakings
of WD-40 will allow the main hull bolts of the Andrea Dora to be removed
by hand. Strangely enough, an integral part of these sprays is the infamous
little red tube that flies out of the nozzle if you look at it cross-eyed, one
of the ten worst tools of all time.
• Margarine tubs with clear lids: If you spend all your time under the bike
looking for a frendle pin that caromed off the peedle valve when you
knocked both off the seat, it’s because you eat butter. Real mechanics
consume pounds of tasteless vegetable oil replicas, just so they can use
the empty tubs for parts containers afterward. (Some, of course, chuck the
butter-coloured goo altogether or use it to repack wheel bearings.) Unlike
air cleaners and radiator lips, margarine tubs aren’t connected by a time/
space wormhole to the Parallel Universe of Lost Frendle Pins.
• Big Rock At The Side Of The Road: Block up a tire. Smack corroded battery
terminals. Pound out a dent. Bop nosey know-it-all types on the noodle.
Scientists have yet to develop a hammer that packs the raw banging power
of granite or limestone. This is the only tool with which a “Made in India”
emblem is not synonymous with the user’s maiming.
• Plastic zip ties: After 20 years of lashing down stray hoses and wired with
old bread ties, some genius brought a slightly slicked-up version to the auto
parts market. Fifteen zip ties can transform a hulking mass of amateurquality
rewiring from a working model of the Brazilian rain forest into something
remotely resembling a wiring harness. Of course, it works both ways.
When buying used bikes, subtract $100.00 for each zip tie under the tank.
• Ridiculously large standard screwdriver with lifetime guarantee: Let’s
admit it. There’s nothing better for prying, chiseling, lifting, breaking, splitting
or mutilating than a huge flat-bladed screwdriver, particularly when
wielded with gusto and a big hammer. This is also the tool of choice for oil
filters so insanely located they can only be removed by driving a stake in
one side and out the other. If you break the screwdriver—and you will, just
like Dad or your shop teacher said—who cares? It’s guaranteed.
• Baling wire: Commonly known as BSA muffler brackets, baling wire holds
anything that’s too hot for tape or ties. Like duct tape, it’s not recommended
for concourse contenders since it works so well you’ll never replace
it with the right thing again. Baling wire is a sentimental favorite in some
circles, particularly with BSA, Triumph, and other single and vertical twins
set.
• A quarter and a phone booth:
See first entry.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact him at
dan@broadcasttechnical.com.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • November 2012 23

This’n’that
In my last column I mentioned that MDCL, in spite of its significant
power savings at the transmitter site, didn’t seem to create any audible
artifacts. I guess the proof comes from an e-mail from Dave Youell,
Chief Engineer for the Bell stations here in Vancouver:
“We did the MDCL conversions on my two main transmitters in April.
Your observations in Broadcast Dialogue mirror what we have observed.
We went with the AMC mode.”
I made the crack last month that Dave Coulter’s CHNL Kamloops (a
Nautel 25 kWatter) was the first conversion of which I was aware in this
neck of these woods, and here Dave Y had already converted his pair of
50 kW Harris blowtorches months ago.
Back to what I said about “you can’t hear the difference” which is
amazing but apparently true.
ENG
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by Dan Roach
AES/EBU Troubles
Okay, not so much troubles as something new to look out for. Mindful, I
suppose, of the extra fragile nature of the thick insulation and thin copper
content of most AES/EBU-compliant wiring, Belden has been marketing a
very nice looking cable with what appears to be an extra-thick neoprene
rubber jacket. Which is a good idea, as far as it goes. The trouble I’ve
discovered recently, on two occasions, is that the extra-thick jacket gets
a severe crunching when you go through the normal exercise of tightening
the strain relief while terminating the cable with industry-standard
XLR connectors … to the point of crunching the inner conductors into
occasional openness. In the vein of all things digital, the faults tend to
be of the on-and-off variety, and you can expect intermittent flashes of
normalcy between the exciting audio failures. This fault can be a bear
to locate!
Ah, Fall Again
It’s time for my annual exhortation to visit your transmitter sites and
button up for winter. The next months may offer the last easy opportunities
until next spring for you to top off fuel tanks and replace belts and
filters and batteries—and that’s just for the emergency generator. Check
that your transmitter building’s gutters and drainpipes are clear. Make
sure the damper motors and thermostats are functioning correctly.
Replace those plugged air filters. Walk around and make sure the varmints
haven’t walked off with all your safety grounds. You’re allowed to think
about applying the high voltage to the tower fences, but you probably
shouldn’t act on the urge.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • October 2012 30

Other autumnal transmitter maintenance items: this is as good a time as any
to replace the batteries in your new micro-processor-driven transmitter, so that
it won’t lose its memory at an inconvenient time (and remember that it’s best
to change the battery while the transmitter is powered up, as otherwise you’re
almost guaranteeing a memory loss).
Any bearings that need periodic lubrication should receive it now. Check
your air handling belts for cracks and wear. Do you have spare line fuses for all
your electrical switchgear? Are they the right size and rating?
Are the towers all standing? Guy wires all where they should be? Don’t laugh
—I once visited an AM site, only to notice guy wire cables lying around in the
field. A tower guy insulator had let go, and the tower was in a precarious state
—but our routine site visit was the first warning that there was trouble brewing.
Since then I try to remember to count the guy wire cables on each tower
whenever I visit a site. And yes, I keep the tower rigger’s telephone number on
speed dial.
Finally, a Puzzler
I recently heard about a strange recurring varmint problem at an AM site.
Like many older AM sites, the tower lighting and pattern change and contactor
interlock wires are direct-buried in backfilled trenches from the transmitter
building out into the field to the tower huts.
I wasn’t there during the original construction (probably the early 1970s) but
presumably the usual precautions were taken: the trench was made 3-4 feet
below grade and backfilled with a little sand, then the wires laid in and topped
with more sand and then backfilled with soil back up to grade.
The problem is that some subterranean critter has apparently developed a
taste for red buried wire (in this case, the pattern interlock) and has been persistently
seeking it out. There are several colours in the trench, but apparently
only the red is tasty enough, and there are gnaw-marks and broken conductors
over a 25-foot length or so of red wire in the trench. So far this has resulted in
many hours of happy digging and searching for the faults. The really alarming
aspect is that after repairs have been completed another piece of broken wire
invariably appears, caused, it is feared, by repeat visits from our wire-avore.
Has anybody heard of a problem like this?
The obvious solution would be to avoid the use of red wiring in future
trenching, though any genuinely helpful solutions to today’s problem would be
appreciated.
How does one encourage a subterranean intruder to go chew on someone
else’s wiring? And what manner of varmint might this be?
Your input is appreciated!
Click the button
for more information.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact him at
dan@broadcasttechnical.com.
To share this article, find the link at http://www.broadcastdialogue.com/stories.aspx
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • October 2012 31

MDCL – Worth a second look?
ENG
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Awhile ago I wrote about the power savings available to AM
broadcasters by upgrading from standard AM transmission
to a more complex form called MDCL, or Modulation Determined
Carrier Level. Sometimes it’s also called DCC or Dynamic
Carrier Control.
In the time since then, quite a few U.S. broadcasters have experimented
with MDCL, in markets large and small. In our own
backyard, CHNL Kamloops has been doing some of its own research
as well, using their new Nautel NX25. There may in fact be other
Canadian broadcasters which have tried this but their efforts
haven’t yet reached my ears (so if you’re up to something here
please let me know!).
by Dan Roach
The Short Story
There are two main schemes, AMC and DAM. Each of them has
a couple of sub-schemes or settings that can be adjusted for those
who just can’t leave well enough alone.
AMC, developed by the British Broadcasting Corporation, starts
with standard full-power AM when the modulation is zero and
gradually reduces carrier level as modulation is increased. This
is done in a fashion that is intended to trick AM receiver AGC
circuits into increasing their gain at the same time the carrier is
reduced, which will increase audio output and conceal the transmission
trickery!
At 0% modulation, full power ramps back up, giving the station
as much quieting, and coverage, as it would have with standard
modulation. The thinking is that any electrical noise in fringe receive
areas will be masked by the modulation, and not noticed.
DAM, developed by Telefunken, weirdly does almost the opposite
to the same end result—it starts with a (somewhat) suppressed
carrier level but that increases as modulation level goes up. In
many respects, this is like a hybrid form of suppressed-carrier
double sideband and it sounds a lot like the old Kahn Powerside
scheme.
From all the reports I’ve seen, those who have experimented
Click the button
for more information.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • September 2012 36

with the two methods have preferred the AMC algorithm. It’s said to
be more transparent-sounding. It’s also said that emergency generator
supplies very much prefer AMC to the “herky-jerky” power demands of
DAM. It’s also worth considering that all these schemes were originally
developed for shortwave broadcasting, and so for speech modulation. A
music-driven format would not see as much power-saving with DAM for
the simple reason that the modulation is sustained at a higher level (so
there’s less carrier suppression).
Any MDCL scheme will require a waiver of FCC or Industry Canada
rules regarding carrier shift as, by definition, there will be a lot of carrier
shift happening. But temporary experimental waivers are said to be
easily available and permanent ones not much harder. By all reports, anyone
who has tried this experiment has taken steps to make the change
permanent.
Results
Everyone who has taken the plunge reports immediate and significant
results. Transmitter power consumption drops 40% or so. Depending upon
how much of the power bill is used by the transmitter (and not by tower
lights and building cooling fans, for instance), site power bills drop from
20% to about 40%. Every published account states the same thing: astonishingly,
there are no audible artifacts from switching to AMC.
I recently had the opportunity to visit CHNL’s transmitter and to listen
to both standard AM and AMC modes both at the site and on the road. I
can confirm this: there doesn’t seem to be any deterioration in sound or
coverage by adopting AMC.
Depending on your transmitter’s age, conversion costs for solid state
transmitters range from free (as simple as selecting an option from
your transmitter’s menu) to a few thousand dollars for some internal
hardware.
In an unforeseen development that underscores just how much
money can be involved, one of the published anecdotes related just
how much extra it was costing to run the (non-MDCL) standby transmitter
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • September 2012 37

occasionally—even a few minutes use resulted in high demand power
charges for the month.
In this case, these extra charges were all that was required to justify
purchase of a second MDCL kit for the standby transmitter!
As newer transmitters are purchased, I predict we will see more and
more use of MDCL techniques. The costs can be trivial and the payback
is immediate, with no discernable downside: the biggest surprise is that
the migration to MDCL didn’t take place long ago.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
To share this article, grab the link at
http://www.broadcastdialogue.com/stories.aspx
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • September 2012 38

A high voltage repair
survival guide
ENG
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As more and more tube transmitters get replaced by modern solidstate
units, the care and feeding of the high voltage power supply
in the tube transmitter gets more and more demanding. The circuits
are pretty simple, but the parts themselves can be unfamiliar, and
they’re definitely getting harder to replace. Nowadays, we sometimes
have to get creative to keep the old beasts in running order.
Let’s start with the plate transformer and any HV inductors … the
most typical fault is an insulation breakdown, leading to a tripped circuit
breaker. Now if the windings are actually shorted together, you’re in
pretty deep trouble. But don’t discount the chance that the insulation
breakdown is a short to the transformer case itself and thence to ground.
In that case, placing the whole works on a piece of wood (or a phone
book) and floating the inductor case above ground can get you back on
air in short order.
The high-voltage wire that is typically used is not particularly expensive
to buy but it can take ages to get your hands on some. In a pinch,
a piece of coaxial cable will often do the trick. The insulation between
the inner and outer conductors is HV rated; if in doubt consult your RGcable
datasheet.
HV rectifier banks generally consist of series trains of silicon diodes,
chained together to make up the high voltages required. A small ceramic
capacitor, nominally 0.01 uF, is often placed in parallel with each diode.
This tiny but important detail is necessary to keep the diodes all sharing
the high voltage present, which otherwise would be enough to short out
individual rectifiers until the whole bank failed. The parts are typically
mounted on an insulating surface, but care must be taken not to use an
insulator that could build up a static charge and cook our parts that way.
Plexiglas sheet, for instance, is a poor choice in spite of having excellent
insulating properties. Prone to static build-up, it can either pop diodes
directly by subjecting them to overvoltage or it can attract dust that
will then provide a conductive path between parts. Either way, you’re
cooked!
HV filter capacitors are most often oil-filled paper types in cans, or
sometimes mylar or polystyrene-filled cans. If the case is burst or bent,
that’s a bad sign. So is visible leaking of oil. Timely replacement of these
caps is getting very difficult, as many of the former manufacturers of
by Dan Roach
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • July/August 2012 33

these units have gone out of business or have dropped a lot of the parts
that they once made. Substitutions are always fair game, but there are
some pitfalls: AC and DC units, despite being similar in appearance, are
quite different inside, and won’t work well in each other’s circuits. It’s
generally better practice to have two or more filter capacitors of smaller
size, rather than just one cap so that a shorted unit can be removed.
Often the transmitter will function more-or-less normally without it until
a replacement can be located.
Always be extra careful around these high-voltage circuits: Work with
a partner, and make liberal use of the shorting stick!
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
To share this article, grab the link at
http://www.broadcastdialogue.com/stories.aspx
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • July/August 2012 34

Try to remain CALM*: Is this
the end of the loudness war?
ENG
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Recently it was announced that Canadian broadcasting regulations
were going to be joining those from the U.S., the UK, Italy, China
and loads of others in adopting controls for loudness for broadcasters
and distributors. And not a moment too soon! While Canada has
been a bit slow at the legislative end, it may be comforting to know that
CRC (Canadian Research Council) has been front and centre in deriving
what is becoming the new international standard for loudness measurement
and control.
It’s a complicated issue, but after reviewing the new standards, I think
it’s safe to say that the standards makers (the ITU in this case) have taken
a thorny problem and beaten it virtually to death (ITU-R BS. 1770-2)
by Dan Roach
What is Loudness?
Perceived loudness is difficult to measure, but CRC and others have
come up with a definition using DSP (digital signal processing) that measures
very well against the perceptions of 98% or so of the general public
over a range of 50 dB or so, and works equally well for mono, dual mono,
stereo, 5.1 surround or, in fact, any reasonable number of audio channels
for all but the strangest audio content.
Let’s use 5.1 surround as our example because that’s what seems to
have brought all this trouble to a head: Each of the primary audio channels
(L, R, C, LS, RS) is run through a pre-filter that compensates for the
acoustics of the human head (the model assumes the head is solid and
spherical but why quibble over details).
After pre-emphasis, each channel’s level is calculated with a rootmean-square
calculation, then gated, then summed together and logged.
There’s also a little extra weighting of the two surround channels (+1.5 dB
or so) because sounds from behind may be perceived as louder.
All of the calculations are oversampled at 4x the maximum audio
frequency which keeps “flash” peaks from sneaking through without detection.
The effects channel is ignored.
After all this black magic, we are left with a single number, LKFS
(Loudness, K-filtered, relative to full scale). This is a measure of absolute
loudness and, of course, will rise and fall with programming but the
average over a program segment is to be -24 +/- 2 dB. And really, that’s
all there is to that.
You could argue that that’s an awful lot of messing around to come
up with one number, but it’s all easily accomplished with modern DSP
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • June 2012 36

chips and it results in a figure that agrees with the perceptions of virtually all test
subjects. And it takes just about everything into account. And it has no subjective
element. Which takes us to…
Dolby and dialnorm
Dolby Laboratories has done a bunch of work on this, and early on it looked like
they were going to write the book that we’d all follow. Dolby found that listener
perception of program loudness was anchored in whatever level the main dialogue
or narration was at. This level is to be encoded in the digital AC3 bitstream
as dialnorm, or dialogue normal. It’s a number from -1 to -31 dB, related to full
scale. Smart receivers can read the dialnorm value and adjust their volume controls
automatically.
Several problems have appeared with this approach:
1) The dialnorm metadata is set by the program producer, and disparate program
elements are set by different persons—they won’t match.
2) There’s no non-proprietary algorithm available that defines “standard” speech;
and things digress for programs without dialogue. Dialnorm then is supposed to
represent the “element that most captures the listener’s interest.” Huh?
3) Metadata settings are notoriously corrupted and/or lost on broadcast servers.
4) Incoming streams in formats other than AC3 may not have metadata information
at all.
The ITU measurement provides a nonsubjective way to measure the loudness
levels of incoming programs and correct erroneous levels and dialnorm metadata
during ingest.
Click the button
for more information.
Loudness control
To share this article, grab the link at
http://www.broadcastdialogue.
com/stories.aspx
If you’re interested in reading
previous Dan Roach articles, go to
http://www.broadcastdialogue.com/
tech.aspx and select “Roach, Dan”
in the Author tab.
In the end we still need devices to adjust the loudness up and down to comply
with the standards. File-based systems are becoming surprisingly popular, will
examine the files on a server in non-real time and measure and, if necessary, adjust
dialnorm settings, audio loudness and dynamic range. Non-conforming files
can be flagged and quarantined. Different settings could be used for streams for
broadcast and those for Internet or smartphone streaming, for instance.
Online systems similar to the familiar audio processors of yesteryear are also
available. For live content, and possibly for an “insurance” loudness control,
these are still the only way to go.
Even after all this messing around, there are still a number of ways to screw
things up. The ones that I’ve heard about are caused by errors in downmix levels
to stereo and the limitations of AC3 encoders and decoders. More on this later!
If you’re interested enough in the ITU standard to want even more excruciating
detail, try http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1770-2-
201103-I!!PDF-E.pdf for a surprisingly readable spiel of the whole process.
*CALM is the Commercial Advertisement Loudness Mitigation Act, the U.S. law
that has broadcasters all a-flutter south of the border; a potential major new
source of revenue for the FCC.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact him at
dan@broadcasttechnical.com.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • June 2012 37

NAB 2012:
Is that change that I smell?
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If you have never attended a NAB convention, it can be a little terrifying.
One of the first overall impressions you will get after a few hours
of listening to the sales pitches about the latest and the greatest is
that “everything you think you know is wrong!”
I think it’s important to remember that it’s technological change that
drives technical sales, and so there’s a great deal of high-powered marketing
directed at convincing you that change is inevitable and that it
must happen now.
The first part of that statement is true. The second, maybe not so
much.
After a few years of seeing this act in person, one develops a certain
distance and, perhaps, skepticism towards all this. Some would say
cynicism.
Another point to keep in mind is that as Canadians the main pitch is
often only incidentally directed at us. In our happy little broadcasting
backwater, we are often not within sight of the “bleeding edge”—even
sometimes when we think that we are. And that can be a very good
thing. Just remember, for the time being, to keep your distance. Otherwise,
it might be disturbing to witness some of the pitches.
For those of us who have just scrambled (at broadcasters’ great expense)
to install ATSC, it comes as a bit of a shock that not only are folks
pushing out ATSC-2, but that ATSC-3 is also in the planning stages. ATSC-2
is intended to offer mobile TV and video improvements to the system
and has been held up primarily because no one has been able to figure
out how to do all that and remain compatible with all those new TV sets
out there.
ATSC-3 is even more disturbing since they’re not even trying for
reverse-compatibility; everything is up for grabs again including 6 MHz
standard TV channel spacing. One of the gripes from the ATSC-3 group
is that the 1080i format has become far too popular, investing producers
deeper into interlace (new standards will all be progressive scan,
apparently).
Another is that the MPEG-2 encoder used in ATSC is old and holding
back progress (this is, of course, true). But the point to take home here
is that to the manufacturers ATSC is 15 years old, MPEG-2 is pushing 20,
and something new has to be done.
They’re bored. (By the way, note that they’re not trying to pitch this
to consumers, where they might be drawn and quartered.)
by Dan Roach
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • May 2012 43

Over in radio, you hear an awful lot about HD radio and its evolving
problems. Obviously this is a bigger deal in the U.S. than in Canada,
where our HD installations at last count numbered exactly zero.
A paper from Harris Broadcasting, evaluating digital radio progress
and status worldwide, is instructive on several points. It shows quantitatively
that we’re very much at the back of the pack as far as digital
radio rollout goes (along with France), and also there’s a wide variety of
systems out there… HD, various flavours of DAB and DAB+, including one
derived from the ill-fated DMB (Digital Mobile Broadcast TV standard,
now adapted for radio) and an assortment of DRM and DRM+. HD radio is
now in its fourth generation of development.
There is even a move afoot to change the analogue FM stereo transmission
standard, changing the L-R subcarrier from double-sideband suppressed
carrier to single-sideband (this is not a late April-fool’s prank!).
One should perhaps consider the source of most of this racket; a couple
of years ago, the same bunch were calling for HD radio to be deployed as
surround sound; a few years before that, to have the audio bandwidth of
FM stereo transmissions increased from 15 kHz to 17 kHz.
The surround sound idea died a quiet death; unforeseen consequences
of the audio bandwidth extension notion caused some much-publicized
pain and suffering. But these are the sorts of ideas that would occur to an
audio processing company. Change, especially perceived improvement,
drives sales. But let’s make sure we know what we’re doing, and the pros
and cons of an action before we leap.
It would be refreshing, if unrealistic, for someone sometime to just
take a few seconds to recognize the immense cost of doing some of these
things. For broadcasters, the leading edge is a risky and expensive place
to be. If consumers don’t follow along, they’re left hanging (AM stereo?
FM quad? 3D television?)
Of course, you’ll also find ideas on the floor that just make so much
sense, and you’ll wonder why someone didn’t think of them sooner. And
while I think it’s good to be skeptical, one must never lose sight of the
fact that some or all of these “crazy” notions may very well happen in
the long run.
But hopefully not this week.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
To share this story, grab the link at
http://www.broadcastdialogue.com/stories.aspx
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan”
in the Author tab.
Rohde & Schwarz Canada Inc.
750 Palladium Drive, Suite 102
Ottawa, ON K2V 1C7
Phone: (613) 592-8000 • Fax: (613) 592-8009
Toll Free: (877) 438-2880
www.rohde-schwarz.com
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • May 2012 44

Worms from the can:
Audio pre-emphasis run amok!
T
o our list of things that seemed like a good idea at the time, but
which we’d really like to get rid of today, let us add FM preemphasis.
Designers of our FM broadcast transmission system were faced with a
problem; the noise level of audio received by FM increases dramatically
as frequency is increased. Actually, if left to its own devices, it has the
same spectral shape as white noise—double the frequency, double the
noise!
This was an early obstacle to FM as a high-fidelity medium.
Their solution was a reflection of the times. Audio from “natural
sources” tends to have much less audio in the higher octaves. And as
discussed here previously, in the analogue world any equipment in suboptimal
condition (whether it is an older microphone, a misaligned or
worn tape head or an old turntable cartridge and stylus) tended to result
in high-frequency roll off, further depressing the content “up high.”
The solution was to introduce pre-emphasis at the transmitter and
build in matching de-emphasis at the receiver. Boost the transmission of
the treble frequencies up out of the hiss, then roll off the highs a matching
amount during reception to bury that noise. This technique was easy
to apply and found its way into records and tape recordings, and even
early CD recordings as well. But its legacy has been a couple of recurring
problems; some easy-to-solve ones resulting from carelessness and at
least one more that is more subtle and hard to get rid of.
The simplest form of pre-emphasis involves a “hinge-point” followed
by treble boost of 6 dB/octave. The hinge-point is usually created by a
circuit with an R and a C, and when you multiply ohms and microfarads
you end up with a product in microseconds. And that’s why FM preemphasis
is referred to as 75 uS.
At 75 uS, audio at 10 kHz is boosted by almost 14 dB and, by the time
we’ve reached FM’s upper limit at 15 kHz, the boost is 17 dB—a lot of
boost!
European FM stations use 50 uS, which is much more moderate. Early
cassette tapes were 120 uS which is extreme but then so were the hiss
problems with standard cassette tape.
As station technicians, it is quite important to know where in the
program chain the audio is pre-emphasized and where it is not, and the
equipment makers have made it alarmingly easy to apply pre-emphasis
twice, which is never a good idea.
ENG
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by Dan Roach
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • April 2012 36

The more subtle and insidious problem is that modern recordings
don’t follow our assumption above that there will be less high-frequency
content. Audio from modern CDs is not like “natural” audio and often
contains unnatural amounts of material above 10 kHz.
The good news is that our modern processor/stereo generator, properly
set up, will take this into account and limit the high-frequency content
to legal levels. The bad news is that something will have to give.
An old-school processor would reduce the overall audio levels, leaving
a big hole in the sound, with associated pumping and sucking sounds.
A modern box will break the audio into bands, and treat the highs and
lows separately, making sure the total remains legal – but at the cost of
bending the pre-emphasis curve. Now the de-emphasis will not match
the modified pre-emphasis, and we will have coloured the sound.
How to make that colouring as subtle as possible, and covering over
any artifacts, is the stuff of advanced processor design and a big reason
why broadcast processors cost so much more than the stuff the recording
studios and sound reinforcement folks use. But by now it’s too late to
take away the pre-emphasis so that’s the way things are going to be for
the foreseeable future.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan”
in the Author tab.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • April 2012 37

AES/EBU: The battled rejoined
F
aithful readers of this space may recall my previous discussion of
this topic (It’s AES/EBU for you!, Broadcast Dialogue, November,
2007). The earlier article concentrated on the transmission aspects
of this standard, particularly as we use and abuse it in broadcast
facilities.
When we refer to AES/EBU, we usually mean the professional standard,
AES3, which is used for carrying mono or stereo audio digitally from
device to device. It could be any sample rate, although 99% of the time,
it’s 32 kHz, 44.1 kHz, or 48 kHz. These rates originally represented audio
from mass storage, CDs, and R-DATs, but, as mentioned above, nowadays
any old rate will do. Most of the time, the audio samples are 16-bits deep,
although 20- and even 24-bit versions have been developed.
Ever notice that most of today’s technical standards aren’t standard in
the sense that they’re more suites of standards?
AES3 is like that.
It may use balanced pair cables, in which case it will most likely use
an XLR connector for I/O (no doubt so that it will be easy to confuse with
the analogue XLR connectors helpfully placed nearby), but of course, for
AES it’s one connector for both channels. But it could just as easily be a
BNC connector and 75-ohm coaxial or video cable. (The coaxial version
allows longer cables before degradation, but you’ll need to get special
baluns to convert to equipment that wants the balanced connection.)
Signal levels for the balanced version are nominally 5V peak; unbalanced
levels are about 1.2V peak (similar to analogue video).
This is probably where we should introduce S/PDIF (pron: spid-diff)
the very similar consumer standard digital audio interface (Sony/Philips
Digital Interconnection Format). S/PDIF also comes in various flavours,
the most common of which is an RCA phono connector, with coaxial
cable of 75-ohm and peak levels of 0.5V. There’s also a version that uses
fibre-optic cable and TOSlink connectors, with visible red LEDs providing
the signal.
This setup is usually called TOSlink, after the connectors, which were
introduced by Toshiba. And there’s a TTL version with no particular specified
connectors and TTL level signals of somewhat less than 5V peak.
S/PDIF can be found in high-end (and sometimes not-so-high-end) consumer
gear such as home CD players, receivers and such.
If the insulator in the RCA jack is orange-coloured, that’s usually a
giveaway that you’ve found S/PDIF.
Now, here’s where it can get interesting (and by interesting I mean
ENG
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by Dan Roach
Click the button
for more information.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • March 2012 30

that pain will likely be involved. Are we paying attention?): A broadcast engineer
can often be called upon to interface between the two standards. The popularity
of both systems means that the likelihood of this type of thing is probably
on the rise.
S/PDIF is NOT AES3, but the similarities can be extensive. As we get to newer
consumer gear not so much as we shall see. The two standards were designed
to be similar and they carry the payload audio in very similar packages. In particular,
the unbalanced coaxial versions of both systems are similar levels and
impedances. But remember: If it’s an RCA connector, it’s not AES3. The control
bits in the standard are different but much equipment ignores most of these
anyway (there’s a bit in AES3 to indicate pre-emphasis, for instance, which is
seldom used nowadays).
The potential for easy compatibility flew out the window when S/PDIF was
modified to accept multi-channel compressed surround sound. Any S/PDIF transmissions
in surround format are going to need extensive adjustments to get to
AES3. Older S/PDIF devices are more likely to transmit uncompressed stereo,
and so more likely to lend themselves to a hacking conversion. A CD player may
be easily converted; a DVD player or home entertainment receiver is much
more likely to use the S/PDIF for surround.
So, in decreasing order of elegance:
1. there are professional interface devices that will convert between the two
standards. As long as they’re working, your worries are over;
2. not recommended, but sometimes you can interface between the two with
a resistor and a TTL inverter, and sometimes even without the inverter (you
can find these circuits in discussions of AES3 and S/PDIF standards);
3. you can always break down and use the analogue inputs and outputs. Not
pretty, and purists may snicker, but it’s going to work every time!
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact him at
dan@broadcasttechnical.com.
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan” in the Author tab.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • March 2012 31

Ones and zeroes can
take many forms
ENG
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This is another “alphabet soup” column. This time we’re looking
at the various digital standards that we’re liable to run into when
transporting digital signals from point to point. But it’s a rapidlyevolving
world which probably means that most of what is not true today
might be tomorrow and all bets are off by the end of the week!
Around the TV studio, SDI, or Serial Digital Interface, reigns supreme.
There are several flavours for high definition and standard definition signals.
HD-SDI also known as SMPTE 292M, runs on coaxial cable at 75
ohms with a bit rate of 1.485 Gbits/s. Standard definition, which seems
to never be called SD-SDI but just plain SDI, is sometimes called SMPTE
259M and might be running at various speeds from 177 to 360 Mbits/s.
These standards are all very fine at the studio but even the lightest
are too heavy for long-haul transmission, which is where the MPEG
crunching comes in. What comes out might be ASI, or Asynchronous Serial
Interface, which is another 75 ohm coaxial standard. ASI could be running
at any old rate as required, even up to 90 Mbit/s (ASI doesn’t care) but
if it’s an ATSC signal it’s probably 19.392658 Mbits/s, and certainly that’s
where it’s going to end up in the transmitter. This can be important as an
ASI signal is sometimes also referred to as a SMPTE 310M signal, in which
case it must be 19.392658 Mbit/s. Some of the ATSC exciters we run into
right now will do a rate downconversion, and some will not.
So beware!
Of course, being digital devices our new radio and fibre links don’t
much care if they’re carrying video or audio or data. And there are some
older standards that can be carried as well, often not for their original
purpose. T1 (also called DS-1) was developed by AT&T and was originally
meant to carry 24 voice channels from point to point. At 8-bits of resolution
and a sampling rate of 8 KHz, each voice channel or time-slot is a
raw 64 kbits/s. Put all those slots together and you’ll end up with a full
duplex 1.544 Mbit/s. The phone company will often mux (multiplex) a
few voice channels together to make up a broadcast audio circuit and,
of course, you can, too. But because T1 is part of the Plesiosynchronous
Digital Hierarchy (no, I am not kidding! And no, these standards may be
old but they don’t quite date to the Jurassic Era!), clocking between T1
frames is not precise. Your broadcast circuits must all remain in the same
T1 frame to keep their proper phase relationship.
The European telcos chose to build up channels a little differently so
by Dan Roach
Click the button
for more information.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • February 2012 24

the popular E1 standard (their version of T1, now common around here as
well) consists of 32 time-slots with an aggregate bit-rate of 2.048 Mbits/s.
At least their slots are the same size at 64 kbits/s. T1 and E1 were originally
meant to run on twisted pair so they’re nominally balanced standards
and can either be delivered by the phone company in that form
via ISDN Primary Rate Interface. The usual form of delivery is via RJ-45
connector but buyer beware: the wiring scheme for ISDN is not the same
as either of the Ethernet layouts.
Or they can be further multiplexed, most commonly to DS-3 and E3,
which are nominally coaxial, with aggregate rates of 44.736 Mbits/s (672
slots) or 34.368 Mbits/s (512 slots) respectively.
Just to make things interesting, all of the coaxial standards use 75
ohm coaxial cable and BNC connectors. Unless colour-coding or something
similar is consistently used to identify different types of circuits as they
are installed in your rack, they’re all going to look very much the same
afterwards. As do the ISDN circuits and any 10- or 100BaseT Ethernet
circuits that might be floating around.
Good luck, and happy hunting!
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact him
at dan@broadcasttechnical.com.
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan”
in the Author tab.
SCTE Canadian Summit 2012
March 27-28
Toronto Congress Centre, North Building
Toronto, Ontario, Canada
The SCTE Canadian Summit is an international event for cable
engineering professionals focusing on the exchange of technical
information for today and tomorrow.
Don’t miss the opportunity to enhance understanding of new technologies that
are driving growth for the industry, particularly in the Canadian market and abroad.
This year’s Summit examines the impact of integrating new technologies into existing
cable infrastructures. Attendees will gain an understanding of the opportunities
and the pitfalls of technology deployments—all to maximize customer
satisfaction and gain operational efficiencies. The topics on tap for this
year’s event include Advanced Advertising; Business Services; Cloud-
Based Services; Content Delivery Networks; HFC Capacity; HFC
Reliability; Home Networking; IP Video; Network Planning;
Sustainability; Video Quality; and Wireless Access.
Register at http://www.scte.org/summit/
bRoADCASt DIALoGuE—The Voice of Broadcasting in Canada • February 2012 25

Of gain and squint and tilt (Oh, my!)
When we say that an FM or TV antenna has gain, we don’t really
mean it—a broadcast antenna is a passive device and, so,
it cannot increase overall signal power levels. (Patent-holder
wannabees for perpetual motion devices should skip this part. They’ll
find it depressing!) What really happens is that there is an apparent
increase in power in a desired direction which makes it look as if the
signal level has been boosted, compared to our omni-directional or reference
signal. But we must observe conservation of energy (there is no
free lunch). That extra energy must be robbed from somewhere else.
An AM array will tuck in your signal in some directions so as to prevent
interference to neighbouring stations. A parabolic microwave antenna
focuses the signal in a given direction, much like a searchlight. An FM
or TV antenna will use multiple radiating elements, carefully arranged
spatially, and driven with controlled phase and power levels so that a
desired directional pattern is produced. Even an omni-directional multielement
antenna can have gain by focusing energy on the horizon at the
expense of radiated energy up and down.
So much for the basics.
A high-gain omni antenna, then, produces a signal that is increasingly
focused on the horizon. The horizontal beam gets narrower and narrower
as the gain is increased. Our effective radiated power, our ERP, keeps
increasing but now we can see that this is not the same as increasing
transmitter power. This can become apparent when the antenna is way
up high as in on a mountaintop high above our population centre. We
can fall into the trap of using a high-gain antenna here, and most of our
radiation will pass right over top of our market and off to the far horizon.
One solution is beam tilt. By mechanically mounting our antenna at
an angle from vertical, we can force the beam downwards towards our
population centre. Of course, at the opposite azimuth the beam will pull
up above the horizon.
This might not be what we want!
Electronic beam tilt can be used to pull the beam down a little at all
azimuths at the same time. That’s more common. But our beam is still
very tight; we’ve just succeeded in aiming it a little better.
In addition to the main lobe on or near the horizon, any multi-element
antenna will have nulls and lobes in its vertical radiation pattern. Again,
if the antenna is up high over the target area, a null at, say, 24 degrees
from straight down might fall right where we want to have some listeners.
Changing the antenna design is one technique to make this problem
ENG
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by Dan Roach
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • December 2011/January 2012 46

go away, by moving the nulls around; another more general one is called
null fill. The phasing between antenna bays is jiggled a little so that the
nulls are partially filled in. This also degrades the antenna gain a bit, but
it’s generally a small price to pay. Another solution to our problem would
be to use a lower gain antenna, and bring the total power back up by
using a larger transmitter. This way our beam becomes wider and easier
to control. But, of course, now our power bills are going to increase (there
really is no free lunch!).
Incidental lobes can be a problem, too. In addition to the main lobe,
sometimes significant radiation can spill more-or-less straight up and
down. The downward energy can cause problems with Safety Code Six
standards. Some antenna designs are inherently better in this respect
than others. And finally, high-gain antennas can be affected from a phenomenon
called squint. This can happen with a narrowband design with
lots of bays - say more than ten. Antennas that consist of rigid transmission
line with an element every one wavelength are particularly susceptible.
The problem is that as the signal is modulated, the wavelength
changes, introducing an error in the (fixed) interbay spacing. As the bays
are cascaded, the error keeps accumulating. It results in the antenna pattern
changing with modulation, which is never a good thing. The antenna
array can be centre-fed instead of end-fed, which will reduce the problem
a little. If you need that much gain, it’s probably better to look at a more
complex (broadband) design.
Click the button
for more information.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan”
in the Author tab.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • December 2011/January 2012 47

Ramblings about radio –
past, present and ... future?
T
hirty-five years ago, a Dallas jingle company named TM Productions
wanted to promote a bunch of radio station jingle packages
that it had on offer. TM put out an LP (that’s an analogue longplaying
gramophone disc for you newbies) to every radio station in North
America, with samples of their jingles on Side B. But to catch everyone’s
attention, they created a radio play satire of the radio broadcasting business
of the future on Side A.
It was called Tomorrow Radio.
It was very creatively done and it was hilarious, especially for those of
us “in the know”. Tomorrow Radio described a preposterous future: stations
knew how many listeners they had from moment to moment, there
were a zillion specialty formats and all music was digitally retrieved from
a computer’s “memory banks” (Oops, so far it sounds pretty familiar).
Station employees lived in constant fear that their station was being
automated and one of the first tell-tale signs was the appearance at work
of a new coffee machine. The play covered the format change of a radio
station from K-9 Radio: for kids 9 and under, to Punk Country.
Anyway, if you’ve never heard of it, click HERE.
It’s still hilarious!
Many of the preposterous predictions have, of course, come true
though sometimes not exactly as forecast. This got me to thinking about
so many of the things that technology has made easier for us to do in
broadcasting and how some of those things have become passing fads.
Others are so common that we take them for granted.
Very philosophical, indeed!
I guess we need a couple of examples:
Remote broadcasting has been around almost as long as radio. All
those years of ordering telephone lines and of battling and lugging heavy
remote gear. During the 1980s, half of the Vancouver radio stations had
satellite remote trucks and drove them all over town doing regular broadcasts
from the great outdoors. Ironically, now that the combination of
cellular technology and high speed data transmission has made it possible
to do studio-grade radio broadcasting from virtually everywhere with no
notice and little money, we don’t see it used nearly as much as when it
was so much harder and more expensive to do.
Why is this?
Ironically, COFDM technology and microwave radios have now given
ENG
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by Dan Roach
Click the button
for more information.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • September 1, 2011 23

television the convenience of an antenna on a camera that can rove and
report, and the TV stations are REALLY embracing it!
In the 1980s, the remote vans were an attempt to reach out and make
direct contact with the audience; to remain relevant by participating in
activities that mattered to it.
Isn’t this important any more?
Or was all that (sometimes painful) effort ineffective?
We’ve seen automation systems come and go but they’ve stayed on
to the extent that now even non-automated stations have that capability
and often will use it in the off-hours.
The earliest automated stations seldom used voicetracks—they wanted
to but it was too difficult to do it well. We’ve seen the voicetracking process
get streamlined and improved so that it has now become very easy
and very common, and the Internet has made the cost of transmission so
low that it’s not a factor at all.
One of the Vancouver South Asian stations voicetracks a show daily
from Mumbai! But now, many automated music stations seem to be dropping
their voicetracks and are just running music and liners (and commercials)
in their place.
Like the remote broadcasts, voicetracks were an attempt to keep
radio relevant-sounding with the illusion that there was a warm body and
a personal touch involved in sending all those hits out from the station.
Not as good as a live body but more affordable. Was voicetracking a failed
experiment or is it rather that programmers just crave change and want
to try to stand out from whatever the herd is doing right now?
We’re surrounded by change. Look at the formerly-ubiquitous Broadcast
News Report, which at one time could be heard hourly on any medium
or small market station all evening and all night long. Nowadays,
not so much.
CKNW-AM Vancouver, one of the giants in the West, built its numbers
in the 1960s and 1970s by introducing hourly and then half-hourly newscasts
when other stations ran only four or five a day.
Well, the hourlies are still there but the half-hourlies are long-gone
from CKNW’s logs. And many (most?) stations are back down to just a
few newscasts a day excepting, of course, for the all-news formats: and
they’ve gone in the other direction.
It’s all too confusing for a poor broadcast technician. We’ll leave the
programming decisions to the programming people and try to get back to
nuts and bolts next month.
For years, readers
have complimented
Su Wahay on her
graphic design
work for
Broadcast Dialogue.
Very few know that
a number of ads in
Broadcast Dialogue
are also her design.
If you need
cost-effective
graphic design for
ads or brochures,
get in touch with
Su Wahay
su@broadcastdialogue.com
416-691-1372
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact him
at dan@broadcasttechnical.com.
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan”
in the Author tab.
bRoADCASt DIALoGuE—The Voice of Broadcasting in Canada • September 1, 2011 24

Techno-quacks on the march
Do you find that, as one of the few technical persons in your
building, it has become your (perhaps self-appointed) role to be
the voice of reason against pseudoscience and all sorts of flimflammery
directed at your station and its occupants, from without and
within?
It’s nothing new but it sure seems to be getting worse. Perhaps this
is a result of bad karma from all those infomercials we broadcast over
the weekend, offering life everlasting and the prostate of a 20-year-old
if you’ll just buy these miraculous pills.
I’m sure you’ve run into the magic claims of improved audio fidelity by
virtue of “oxygen-free copper” wires to your speakers. And there are the
claims of sonic superiority from tube audio amplifiers, from solid-state
amps featuring “new, patented Class X” circuits, and from loudspeaker
designs with all sorts of weird and wonderful catacombs inside.
High fidelity audio really has generated so much of this stuff that it
could be a subject unto itself. I have an audiophile neighbour who just
had to stuff the walls of his home theatre with a particular brand of rock
wool for the potent sound muffling ability it offers.
At one time or another, your station has probably been approached by
audio consultants trying to sell some obscure audio processor distortion
box guaranteed to generate huge ratings increases.
Certainly in recent years we’ve seen a proliferation of strange microphone
brands with equally bizarre claims. You can perhaps get even more
mileage from this by combining that strange microphone with a matched
tube preamplifier. It’s even better if the tube preamplifier has a flashy
display or perhaps a fuchsia pilot light!
Then there’s all the B.S. spread around in the music recording industry.
This is sometimes similar to the audiophile variety and shares with it
the characteristic that “it just sounds better.”
Forget about trying to refute any claims from this quarter, no matter
how silly, by using logic or test instruments … these folks can hear things
that the test equipment can’t. And no amount of reasoned argument is
going to change the minds of the true believers.
It goes almost without saying that any loudspeaker will sound better
with its grille removed, although sometimes it becomes necessary to stuff
toilet paper into the resultant exposed ribbon tweeters to make them
sound a little less harsh. I have seen “scholarly” write-ups in recording
industry trade magazines go so far as to extol the virtues of particular
brands of toilet paper that can be used for this purpose.
ENG
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by Dan Roach
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • July 12, 2011 28

These quacks don’t even have to be internally consistent: on the one
hand we can claim that an old tube amp, perhaps costing ten or twenty
kilobucks and using technology from 80 years ago, is better than anything
made with today’s technology. At the same time, someone, somewhere
not too far away, will tell you that anything digital is inherently better
—just because it’s digital!
It was that old wag Arthur C. Clarke (creator of 2001: A Space Odyssey
and inventor of the geosynchronous orbit in his spare time) who stated
that any sufficiently advanced technology becomes indistinguishable from
magic.
Now that we’ve reached an age when the common person cannot or
will not grasp even the most basic of scientific principles, it seems that
we’re doomed to be inundated by more and more sincere-sounding scam
artists.
I recently heard of a salesperson at one of the big box stores explaining
to his poor victim that a certain brand of memory card (for a digital
camera, in this case) was the particular favourite of professional photographers
everywhere. The reason: this card was so advanced that any
pictures taken with a camera using it would boast more vibrant colours.
Kodachrome, meet the digital age!
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact
him at dan@broadcasttechnical.com.
If you’re interested in reading previous Dan Roach articles, go to
http://www.broadcastdialogue.com/tech.aspx and select “Roach, Dan”
in the Author tab.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada • July 12, 2011 29

The capacitor plague
Robert Orban (of Optimod fame) used to say, semi-seriously, that
“you can’t trust the green ones”. They’re in everything electronic
and their premature failure may be gradually bringing the consumer
electronics industry to its knees all around us. Why is it that we apparently
have lost the ability to make a decent, reliable electrolytic
capacitor?
This is a high-tech horror story: of industrial espionage gone wrong,
of technology without borders and of the growing interdependency of
all things. It is a case of truth being stranger than fiction. And it is a
story that, although it started in the mid 1990s, continues to unfold to
this day.
There’s a reason that all our electronic products seem to work fine
right after we plug them in, but start to misbehave somewhere between
six months use and the end of warranty. Whether we’re talking about
a computer motherboard, a DVD player or a TV set, there’s a bunch of
electrolytic capacitors inside, and some of them are likely literally boiling
away with every use.
“Electrolytics” have been with us since the dawn of electronics.
There’s been increasing pressure to make them smaller, with lower ESRs
(equivalent series resistance) and higher performance, and to make them
in a surface-mount form factor. All of these developments have required
extensive research and development, and where there’s money being
spent on R&D there’s also, apparently, industrial theft.
A Japanese capacitor company developed a superior electrolyte recipe
in the early 1990s. One of their scientists left and joined a Taiwanese
capacitor company where he duplicated the first company’s secret recipe.
A few colleagues at this second company then departed and started
working for a third company where they successfully reproduced most
of the stolen recipe. But some critical components were missing … some
chemicals that would prevent the resultant capacitors from breaking
down and blowing up after a short period of use.
ENG
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by Dan Roach
What Happens?
The electrolyte inside these capacitors is a corrosive aqueous solution.
The missing chemicals were put in there to keep the electrolyte
from breaking down in the presence of electric charge. Lacking them, the
paste inside our defective caps does just that, releasing hydrogen gas.
bRoADCASt DIALoGuE Technology Insider • June 14, 2011 18

The pressure inside typically builds up until the capacitor bulges or bursts,
releasing corrosive electrolyte solution (at this point it hasn’t all broken down
yet) which as often as not spills out on our circuit board and either burns off
some traces or provides a conductive path on the board where none should
be. Either way, this generally means fireworks.
Even though the problem has been identified for several years now, there
are zillions of bad caps out in the system and they continue to be used in
production, and they continue to cause premature failures. Next time you
purchase anything electronic, it might be wise to reconsider that extended
warranty option!
Further Reading
This worldwide story was first uncovered by the Toronto Star. Further
details can be found in Wikipedia under the heading “Capacitor plague.”
Two University of Maryland researchers performed a detailed analysis of the
chemistry involved in the failures. They can be found HERE.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract
engineering firm based in Vancouver. If you have a question or comment, contact Dan
at dan@broadcasttechnical.com.
bRoADCASt DIALoGuE Technology Insider • June 14, 2011 19

AM dynamic carrier control?
A true story!
Idon’t think it’s any surprise to anyone in our business that AM broadcasting
can be a pretty expensive proposition. Aside from the usual transmitter and
equipment costs, there’s often a great deal of transmitter site land tied up, extensive
civil works and big power bills to boot.
Those power bills don’t look to be getting any easier to handle. According to
the local utilities, we’ve been living in a subsidized bubble and the end of the
“easy times” is approaching rapidly, perhaps never to return. In B.C. we’ve been
told to expect fifty per cent increases in electric power costs over the next few
years, just for starters.
Yikes!
When one’s already subjected to transmitter power bills in the thousands of
dollars per month, how is one to make ends meet when all this comes to pass?
For an unusual answer to this problem, one might turn to the story of Chuck
Lakaytis, the director of engineering for the National Public Radio stations in
Alaska. NPR runs a network of stations, including many AM stations, throughout
the more populated parts of Alaska. They’ve already been hit with huge power
bill increases as most of the power generated there comes from diesel generators.
And the increasing fuel transport costs coupled with the increased costs
of the fuel itself have hit them hard.
There’s no end in sight.
They’ve contemplated shutting down their AM rigs and replacing them with
FM for the power savings, but in the remote north nothing gets out into the remote
areas like AM.
Lakaytis has been experimenting with, and has become a proponent of, a
technique called Dynamic Carrier Control. Simply put, this is a modification of
standard amplitude modulation designed to save on power consumption. While
this sounds kind of quaint to our ears, evidently BBC and other heavyweight
broadcasters overseas have been working on this for decades and have found
algorithms that will reduce the power bills but result in transmissions that
sound good on standard AM receivers. If you’ve listened to BBC on LW, MW or
SW overseas in the last 30 years, chances are you’ve been listening to one of
these broadcasts without realizing it.
There are two contrasting techniques out there: the BBC has AMC, and the
Germans and Swiss have been tinkering with DAM and DCC. AMC reduces carrier
power during peaks of modulation and restores the carrier to full power
during silence in order to get the receiver into full quieting. The carrier level
is reduced in such a fashion that the receiver’s AGC is prompted to increase
ENG
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by Dan Roach
Learn about the new
compact broadcast
console C10 HD
Click the HHB logo.
BROADCAST DIALOGUE Technology Insider • April 19, 2011 14

gain, compensating for the reduction. This creates the curious condition that
the Tx output is, say, 10 kW at zero modulation, but that drops down as modulation
percentage increases.
Ironically, the mainland European system works in a contrary manner: As
modulation increases the carrier, which was suppressed, increases in level. This
approach sounds sort of like a form of SSB transmission or perhaps a bit like
Kahn Powerside.
Alaska NPR has experimented with both systems, using modern Harris and
Nautel transmitters, and has done enough field work to expect transmitter site
power reductions of 30-35% from normal broadcast with no deterioration of received
sound, no Tx power reductions and no complaints. In order to make this
legal, they need to get FCC waivers on transmission, as either technique almost
by definition, is going to play heck with the carrier shift regs, among others.
They’re in the process of getting permanent waivers for their test sites and applying
for more for the rest of their AMs. Chuck Lakaytis says he’s amazed that
this hasn’t come up before in North America. As our power bills spiral inexorably
upward we might start to wonder the same!
Lakaytis presented a paper at this year’s NAB Engineering convention. If you’re
interested in Dynamic Carrier Control for AM, there’s some technical information
available at the Nautel web site, www.nautel.com.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact Dan at
dan@broadcasttechnical.com.
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PLAYOUT SYSTEM.
ADAVANCED RADIO AUTOMATION
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RELIABLE, INTUITIVE, FLEXIBLE
BROADCAST DIALOGUE Technology Insider • April 19, 2011 15

We all could use a good belt
now and then…
There’s no escaping the V-belt. Newer transmitter designs seem to be going
more towards either a direct drive blower arrangement or an array of muffin
fans or something similar. Nevertheless, you’re still almost certain to run
into V-belts in the transmitter building and studio HVAC designs, in emergency
generator systems, and most mechanical systems that we encounter. Even
though V-belts remain ubiquitous, there’s a surprising amount of information to
know about them.
Much information is contained in the part number. If there’s an “L” in the
middle, e.g. 2L200, or 4L410, it’s designated an FHP or “fractional horsepower”
belt, and designed for light duty work, like a home furnace fan, for instance.
Other than for wall-mounted exhaust fans or really small transmitters, you’re
more likely to run into the “A” and “B” series of belts. These are heavier duty
and capable of transferring drive powers of several horsepower. If you have a
system that needs to have the belts slip a little on startup (a “clutching” action),
these belts can sometimes do that. “A” belts are narrower than “B” belts,
which are narrower than “C” belts, etc.
Next up on the ruggedness scale are the “X” belts: “AX,” “BX,” et cetera.
These belts have a “cogged” design (i.e. they have teeth), so that they can
flex better around the drive sheave, and also they will run cooler. The sides of
the “X” belts are rougher, so they grip more aggressively, and for this reason
this type shouldn’t be used if “clutching” is needed.
From a casual user’s viewpoint, the sizing of V-belts is more complicated than
it should be. “L” series belts are sized based on outside length (e.g. a 2L200
belt has an outside length of 20 inches), the “A” belts are sized based on inside
length (e.g. an A51 belts has an inside length of 51 inches and an outside
length of 53 inches), as are “B belts (e.g. a B93 belt has an inside length of 93
inches and an outside length of 96 inches).
Tensioning of belts is key: if they’re too tight, bearing wear is greatly accelerated.
If they’re loose, the belts slip and wear quickly. Often you’ll read that
you should be able to press on the belt at a point halfway between the sheaves,
perpendicular to the direction of travel, and displace the belt about one inch
if the tension is correct. Of course, to do this you’d have to know how hard to
press on the belt but you get the general idea.
When you’re running two or more belts in tandem, they will share the load
better if you can use a matched set. Many vendors won’t select them for you
that way anymore, but you can often get a pretty good match by looking for
small markings placed on the outside surface of the belt. When V-belts are
manufactured, several are cut from a large webbing, and the webbing number
(sort of like a lot number) is often stamped on the outside surface of the belt.
ENG
INE
ERI
NG
by Dan Roach
BROADCAST DIALOGUE Technology Insider • March 22, 2011 29

When you pick up a few belts of one size at the same time, many times several
will have matching webbing numbers.
Match them if you can.
You can calculate the rotation speed at the output of a belt system easily
enough just by multiplying your motor RPM by the ratio of motor sheave diameter
to output sheave diameter. Always take care to inspect the input and output
sheaves to make sure that the belt(s) travel in a straight perpendicular path
and that the sheave notches line up exactly. If the belts are allowed to ride up
on one side or the other of the sheave, that’s trouble brewing.
Another potential source of trouble occurs when the belt is forced to flex too
much. For instance, if one of the sheaves is too small. The result is premature
belt failure. The obvious solution is to increase the size of the small sheave.
(Minimum sheave diameter and maximum load transfer power are specified for
V-belts, you just have to look them up on a list that has everything you need to
know at http://www.friesen.com/electric/FHPFractionalHorsepowerVBelts.pdf).
If the output RPM needs to be held the same, then you’ll need to increase
the diameter of the large sheave as well to keep them in the same proportions.
Last month we were talking about routine inspections that can prevent mechanical
failure. V-belts need to be looked at every few months for telltale signs
of wear. Do it as a matter of course at lubrication intervals. If you find cracks
or delamination of a belt, change it forthwith.
It’s always a good idea to have a couple of extras of the right size on hand.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact Dan at
dan@broadcasttechnical.com.
BROADCAST DIALOGUE Technology Insider • March 22, 2011 30

Stuff to do before something breaks
ENG
INE
ERI
NG
Just as you should check your smoke detector batteries are still okay every
time you “spring ahead and fall back” for Daylight Time (and of course you
Saskatchewanians should, too, twice a year at the occasion of your choice),
there are a number of things you should be checking every so often around your
studio and transmitter site to make sure equipment will work for you when you
need it.
Foremost of these items is checking your UPS batteries. Really, it would be
better if these things came with a best before date, because fail they surely
will. Next best thing, of course, is to write the date you change the batteries
on the UPS in felt pen. That way you’ll know if the replacements need replacing
at a glance. Some gel cells are better than others, but any cell still in use
after four years or so is overdue to fail. Some of the cheaper brands are only
good for two years.
While we’re discussing batteries, don’t forget the little memory batteries
inside newer transmitters and remote control systems. And be sure to think for
a second before you pop the old one out—this is one occasion where you want
to perform the operation with the power ON. There’s not much sense in shutting
the power off when you’re going to replace the battery that helps the machine
remember its state when you shut the power off, if you get my drift.
Nearly everyone seems to have cut back on standby generator maintenance
visits, and by and large we do seem to be getting away with it but that also
means that the burden of monitoring the engine’s health now falls more on
someone else, e.g. you, probably. I know it seems like an expensive proposition,
but the pros will replace that starter battery at less than five-year intervals. If
you have spent the money to have a standby generator then it behooves you to
make sure it will work when called for. So check those oil levels, make sure the
V-belts are in good shape and get the oil changed every 250 hours or so of run
time. Make sure your battery’s water levels are correct and the terminals are
clean. And a full load test every month or so is your only reassurance that the
generator will work when the lights go out. One item that is often overlooked
for the sake of convenience is the main power switch and transmitter supply
switches. These should be exercised at least once a year or so to make sure they
aren’t jammed in the on position.
It has been mentioned here before, but it does bear repeating, that periodic
visits to the transmitter site should include inspecting the air filters and belts
both in the transmitter and in the building’s HVAC system. A little lubrication
wherever it’s needed will pay off in reliability as well. Here on the wet coast,
we also have to keep an eye on rooftop gutters, generally just before the rainy
season, to make sure that leaves and gunk don’t plug up the downpipes. It’s oldby
Dan Roach
Click the button
for more information.
BROADCAST DIALOGUE Technology Insider • February 8, 2011 16

fashioned but I always like to have a max/min thermometer hanging in the
transmitter room as well which you can monitor on site visits to make sure that
temperature controls are still functioning and compensating properly for ambient
temperature changes while you’re away.
Done carefully, a little periodic inspection and maintenance of all things
mechanical will always pay dividends in reliability. Now if we could just predict
when the fans and hard drives in our computers are going to fail we’d be on easy
street!
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact Dan at
dan@broadcasttechnical.com.
BROADCAST DIALOGUE Technology Insider • February 8, 2011 17

Sins of the past revisited:
RDBS best practices
ENG
INE
ERI
NG
broadcasters in Canada continue to embrace RDBS technology, at least
FM at the lower levels. It’s easy to see why: it offers some neat features,
and the entry level is very inexpensive indeed ($500). We’ve covered the
basics before. Today, we’ll dig a little deeper and try and help you avoid a couple
of the pitfalls. We know about these ones because we’ve taken the time to
personally fall into them.
Much of the recent interest in RDBS must be because the last couple of generations
of iPods and other MP3 players with FM tuners (Zune, et al) have incorporated
RDBS decoders, and then some.
by Dan Roach
My Injection Is Your Deviation
One of the most important parameters that you must get right is the injection
level of the RDBS subcarrier onto the FM signal. By this we mean the
amount that the RDBS sub is allowed to deviate the FM carrier. (Broadcasters
use the term “injection”; others often refer to “deviation.”) RDS standards
documents allow an injection between 1.3% and 10%, with most users settling
on 2.7%. Injection is normally expressed as a percentage of 100% modulation,
which is defined as 75 kHz deviation, thus the typical 2.7% injection is the same
as 2 kHz deviation. CRC RDBS maven Julie Phaneuf advises that the super subminiature
receivers built into those iPods prefer a higher injection level of at
least 5.3% (deviation of 4 kHz) for reliable operation. If iPod RDS reception is
important to you, you should at least consider increasing your injection level
to best accommodate the new radios.
This brings up the whole issue of how do I measure RDBS injection? The only
accurate way that I know is to cut all other modulation and measure the RDBS
carrier on a total modulation meter monitoring your main carrier; it’s a very low
level, but modern exciters with x10 scale can handle this quite well. Older
stereo monitors and SCA monitors often have a “total modulation” position and
a meter multiplier that will serve nicely as well. The tricky part is that the
RDBS carrier is clocked as the third harmonic of the 19 kHz pilot, so if you kill
the pilot, you might lose the RDBS, depending on the brand of encoder, and
the configuration you’ve chosen. So you need to configure in such a way that
you can feed the transmitter the RDBS signal and nothing else, for measuring
and adjusting purposes. With the pilot also on, your measurement of the RDBS
carrier is hopelessly swamped.
Get Your PI Code Right
While you’re hurrying to get your RDBS encoder installed, it’s very tempting
BROADCAST DIALOGUE Technology Insider • January 11, 2011 19

to overlook the PI code. Some of the units made in the U.S. have PI code calculators
that don’t work on our Canadian call letters, and the Europeans have
another whole different way of working out their codes. RESIST THE TEMPTATION.
Leaving the PI code empty or at “0000” can do very bad things to some receivers.
Ahem, for instance, there was an earlier model of Rolls Royce car radio that
would not only seize up, it would also lock up the integrated climate control system
after it received this invalid code. (Ask us how we know all this…).
Anyway, you have no excuse anymore, because Julie Phaneuf (remember her
from earlier in this column?) has provided a free Canadian RDBS code calculator
for you at http://mmbtools.crc.ca/content/view/49/75/
You’re welcome.
Thanks and a tip of the hat to Julie and all the good folks at Communications
Research Centre Canada.
PS Codes: to Scroll or Not to Scroll?
Read the standards literature and you’d think that turning on scrolling PS will
have the RDBS police hunting you down and hauling you off to points unknown.
And yet, if you turn on your radio, you’ll find that everybody else does it. The
standards groups don’t like it, the Europeans really don’t like it, but here in North
America, it’s a fact of life. Everyone wants song title information on the screen
(as well as their call letters of course), and this is the only way to get it on the
fronts of most car radios. But because you’re not supposed to do it at all, different
receivers react differently… if you scroll too quickly, some receivers may
drop letters or otherwise behave erratically. So be careful! Enuff said.
While you’re at it, many RDBS receivers will automatically synchronize their
clocks to your RDBS encoder time signal if it’s enabled. If you’re not going to
keep your clock accurate, make sure your encoder knows. Otherwise you risk
unhappy listeners (“CXXX, your late-to-work radio station!,” though amusing is
probably not a winning format.)
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a contract engineering
firm based in Vancouver. If you have a question or comment, contact Dan at
dan@broadcasttechnical.com.
BROADCAST DIALOGUE Technology Insider • January 11, 2011 20

ENGINEERING
DRM plus: for us?
BY DAN ROACH
I’ve said it before, but we sure live in
interesting times. And a confluence
of events could just result in yet
another opportunity for meaningful
change in the technical side of radio
broadcasting.
No, I really mean it this time. After
AM stereo, L-band DAB, HD Radio in AM
and FM flavours (and not even mentioning
FM quad, Dolby FM and other oddfellows),
I think most everyone in the
business has had a bellyful of all these
proposals.
But consider this: the forced abandonment
of the low VHF channels by digital
television leaves some additional spectrum
that could be used to extend the
FM band. Instead of more of the same
analogue FM, or the compromise solution
of Ibiquity HD FM, what if the FM
band were extended downward and allocated
for DRM+ transmissions only?
Let’s start at the beginning. DRM
stands for Digital Radio Mondiale, which
is a European open standard for digital
broadcasting, originally in the AM and
shortwave bands. It’s been around for a
while, and it actually works very well even
with the channel distortions and fading
that are common on shortwave. It is very
spectrum-efficient. It is a true digital format,
and doesn’t try to simulcast an analogue
and a digital signal*. As a result, it
is incompatible with analogue radio although
it has been designed so that conventional
analogue transmitters, antennas,
etc. can often be converted to the digital
standard.
DRM+ is the latest incarnation, and
is intended for higher frequencies, to the
top of our FM band. Since it’s open source,
there are no recurring licence fees as with
Ibiquity. In fact, many shortwave users
have connected their analogue SW receiver
to their personal computer and decoded
audio with free software available over
the Internet.
In Canada, the FM broadcast band is
reaching full saturation in populated areas,
and near the U.S. border. FM expansion
has been on the minds of broadcasters a
great deal of late. By utilizing DRM+,
many more channels could be allocated
than with analogue FM (current configurations
call for 100kHz carriers, each with
four stereo programs).
The availability of alternative services
using DRM+ might drive receiver sales,
in a way that our simulcast of the same
old stuff on DAB did not. Because we are
dealing with the frequency spectrum we
already know, propagation models would
be more similar to existing broadcast, and
not like L-band (i.e. transmitter sites as
we know them, and not a whole mess of
cellphone-like repeater sites).
The FM expansion band could give
existing AM stations an orderly migration
path to FM. Alternatively, if the expanded
FM band were to gain market acceptance
it would be a smaller step towards
digital usage of the current AM bands.
That could provide for true wide-area
coverage of single stations (on AM), but
with better quality audio than we have
been used to (stereo audio, RDS functions,
etc.).
The timing couldn’t be worse: we’re
all sick to death of all these proposals
and their variants. On the other hand, we
have the plausible availability of more
spectrum, the maturity of DRM+ technology
and the recent arrival of MPEG-4
compression all happening right now.
This opportunity might be too good
to pass up.
* Okay, that’s not entirely accurate. There
is provision for some simulcasting,
splitting the channel into analogue
and digital sub-bands in a fashion similar
to HD Radio. But it’s only one option,
and we’d probably all be better
off if we pretended it didn’t exist at all.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
54 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada DECEMBER 2010/JANUARY 2011

ENGINEERING
…and thus the whirligig of time
brings revenge
BY DAN ROACH
Have you been following the
goings-on of the Blu-ray disc?
The executive summary would
be “not well”*.
Despite glowing predictions from the
designers of this latest technology, from
the folks that brought you various types
of CDs and DVDs (Sony, basically), apparently
Blu-ray progress is only “okay”.
Consumers are buying enough stuff that
the standard will carry on, but nobody’s
getting rich at it yet.
This is in spite of the fact that prices
of discs and players have fallen much
more quickly than predicted. Blu-ray players
started at more than $1,000 and now
it’s common to see them going for $150
or so at retailers. And discs are just a couple
of bucks higher than regular DVDs,
in spite of higher mastering and production
costs.
The stores are certainly doing their
part; the relative size of the Blu-ray disc
retail displays would lead one to believe
that DVD sales are all but dead. The truth
might surprise you—as of last December
in the United States Blu-ray disc sales were
only 14% of DVD revenues; and Blu-ray
profits considerably less.
Consumers, it would seem, are largely
refusing to buy the blue laser discs.
This is in spite of brisk sales of largescreen
high definition television sets,
which it had been thought would drive
take-up of the new technology. Early consumer
confusion over the competition between
HD-DVD and Blu-ray should have
dissipated by now. Some observers have
surmised that the surprise appearance of
low-cost conventional DVD players with
internal upconverters, that gave the output
a “pseudo-high-definition presentation”,
have led scores of consumers to stay away
from Blu-ray—at least for the time being.
All of which causes one to recall the
lack of enthusiasm evinced by one Bill
Gates, he of Microsoft fame and fortune,
during the early stages of the HD-DVD
vs. Blu-ray hi-def disc wars (a good five
years ago). His take took many by surprise:
it amounted to “who cares?” Gates
predicted that whoever won the battle,
their victory would be short-lived because
the discs would quickly be supplanted by
the arrival of low-cost, high-capacity hard
drives and high-speed Internet to consumers’
homes.
It’s always dangerous to bet against Bill.
Two recent news items: Blockbuster in
the U.S. is seeking bankruptcy protection.
Netflix, also much in the news, seeks to
replace its movie disc-by-mail business
with a streaming-delivery model. The notion
of picking up and renting a movie
and taking it home for playback seems
to be falling out of favour with consumers.
Not good news for Blu-ray.
What has all this to do with our broadcast
environment?
Not so much directly. But the slow
development of Blu-ray as a successful
consumer medium may mean that the
projected ancillary uses, of more interest
to broadcasters, e.g. as a mass storage
and back-up medium for computers and
as storage for video HD handicams, may
never come to pass.
It also underlines the great uncertainty
that surrounds whether any new technology
will ultimately have a short, a
long, or no life at all. For every success
story (VHS, CDs and DVDs, perhaps),
the byways are littered with Elcassettes,
Betamax, r-DATs, minidisks, 16 RPM records,
laserdiscs and all forms of quadraphonic
recording.
Rather than “if you build it, they will
come”, a more appropriate slogan might
be “you can lead a horse to water…”
And always: “let the buyer beware.”
* see Dipert, Brian, “Blu-ray: Dogged by delays, will
it still have its day?”, EDN, July 2010, Page 28.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada NOVEMBER 2010

ENGINEERING
RF dentistry: Filling your
cavity’s needs for repair
BY DAN ROACH
What’s that ancient curse: “May you
live in interesting times!”?
Lately, I’ve been discovering firsthand
just how exciting and challenging it can
be to be carrying on in these “interesting
times”.
Anyone who is maintaining an analogue
TV transmitter in Canada will be
able to appreciate our unique position
right now. As we all know, analogue TV
transmission stopped in the U.S. last year.
And for the last few years, we’ve known
that ATSC is coming our way, too, so
there’s been very little in the way of
incentive to replace existing analogue
transmitters in this country.
Now we’re down to the last year of
the old technology. Which puts us in a
very unusual position—broadcast operators
are more reluctant to keep investing
in the old technology, but will nevertheless
want those old transmitters kept running
to the bitter end.
Manufacturers have long since moved
on to more modern designs and really
aren’t able to support their older designs,
even if they still want to, which they
probably don’t. On top of this, with the
disappearance of the U.S. market for
maintenance parts, we in Canada are left
with what looks to manufacturers like just
a handful or so of old transmitters to
maintain. So support from the transmitter
makers has been drying up rather
quickly.
This problem is way over and above
the well-known phenomenon of the disappearing
semiconductors. Just procuring
proper replacements for almost any
blown semiconductor “of a certain age”,
especially RF power transistors, is an increasingly
difficult task that we will have
to discuss another day.
Which brings us to the specifics of my
current project.
I had the misfortune recently to have
a high-power visual tube cavity burn up
some parts inside. My experience in the
past has been to carefully disassemble
the cavity, identify the fried mechanical
components and place a call to the manufacturer,
who would then promptly ship
me shiny new replacements, coupled with
useful applications advice if necessary. A
little cleaning, some careful reassembly,
and we’re back in business.
While not the most pleasant of duties,
it is necessary only occasionally in the life
of a transmitter, and is soon forgotten
under the pressure of more frequent tasks.
Well, that was the past. Now I’m discovering
that shiny new parts are out of
the question, useful advice is hard to come
by and even rebuilding of the cooked
mechanical components has most likely
become a local (i.e. self-serve) affair.
Let me be clear, I’m not blaming the
manufacturers—not only do they have
to lead the market if they’re going to survive,
but support for some of these old
beasts is also getting to be very difficult,
even for them. With the turnover in staff
at transmitter factories, there are very few
technicians left at the plants that have
ever worked on these older models, and
even fewer that can remember the details.
So now, on top of everything else, we
have to become materials procurement
specialists.
Thank heaven for the Internet! Where
else can you find unusual supplies like
finger stock, specialty non-ferrous fasteners
and Teflon adhesive-backed tape?
It’s ironic that, just as the need for
detailed knowledge about the properties
of materials in high-power tube RF cavities
is drying up over on the design side,
we’re having to learn all these things for
the first time in the field. Oh yes, we’re
just “livin’ the dream!”
We’ve gone from “Nature abhors a
vacuum,” to “Nature abhors a vacuum
tube RF cavity!”
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
34 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada OCTOBER 2010

ENGINEERING
Reflections on standing waves
BY DAN ROACH
One of those parameters that we
all jabber about frequently in the
transmission game is Standing
Wave Ratio, or SWR. It’s a pity that there’s
so much misunderstanding surrounding
an essentially simple concept.
Your transmitter is connected to your
antenna, or load, with a length of transmission
line. Transmission line theory tells
us that in an ideal, lossless world, if all
three of these items are perfectly matched
(at 50 ohms, or whatever), then all of the
RF energy leaving the transmitter will arrive
at the antenna and be radiated from
there. In the real world, there will be
some slight attenuation from the transmission
line, and some of the energy
that does make it to the antenna will be
reflected back to the transmitter by slight
impedance mismatch.
The phase difference between the forward-going,
incident wave and the reflected
wave varies along the line, but is
constant at any point on the line. This is
where the expression “Standing Waves”
comes from—although the waves actually
travel along the line, the voltage nodes
appear to be stationary.
Where the voltages of the incident
and reflected waves are in phase, there is
a maximum, and where they are out of
phase a minimum. The Voltage Standing
Wave Ratio, or VSWR, is the ratio of the
magnitude of the maximum voltage on
the line to the minimum. There is also a
Current Standing Wave Ratio, which will
have the identical value, so clearly the V
in VSWR is not needed and we can simplify
our expression to SWR without giving
up anything. (The continued popularity
of that V in VSWR is another one of the
great mysteries of our age.)
A perfect load would result in an
SWR of 1.00; an open circuit or a short at
the end of the line will give us an SWR
near infinity (there is some attenuation
that keeps us from getting all the way
there).
An alternate expression we don’t use
much in broadcasting, perhaps to our
own misfortune, is Reflection Coefficient,
which is simply the ratio of the reflected
wave voltage to the forward wave voltage.
A perfect match gives a reflection
coefficient of 0; a short-circuit load has a
coefficient of -1.0, and an open circuit’s
coefficient is +1.0. Conceptually, this is a
little simpler to grasp than SWR. But it
amounts to the same thing.
Next comes the very popular, but perhaps
overused, expression of Return Loss.
If we take 20 times the logarithm of the
ratio of the magnitudes of the reflected
voltage and the forward voltage, we end
up with a number in decibels that represents
the power “lost” in the load between
the incident and reflected waves.
One of my favourite textbooks describes
this whole concept as “silly”.
Nevertheless, it remains popular, probably
because we all know how much engineers
love to express things (all things,
really) in dB. But when we get right down
to it, a low value of return loss means the
same thing as a high value of SWR—
trouble coming up ahead, fast!
Those high SWR values mean that the
peak RF voltage at “nodes” on the line,
where the forward and reflected voltages
add in phase, will be high. As the waves
bounce back and forth repeatedly between
source and load, that voltage can become
very high. If it exceeds the dielectric breakdown
voltage of the line, arcing will
ensue. That Teflon insulation will break
down to carbon and now we have a
short. The short gives us another point of
high reflections, and so the cycle continues
back towards the transmitter.
Aside from the transmission line damage,
the transmitter doesn’t care much for
the mismatch either. Again, peak voltages
and currents are suddenly much higher
than planned for and will stress the amplifier’s
components. Even if the parts aren’t
overstressed to the point of failure, efficiency
drops and temperatures rise. At
broadcast power levels, something generally
has to give pretty quickly. Which is
why so much attention has gone into
SWR detection and power foldback from
manufacturers!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada SEPTEMBER 2010 39

ENGINEERING
Engineering notes from NAB 2010
BY DAN ROACH
As always, the exhibit floor at NAB
2010 in Las Vegas was filled with a
combination of the new and novel
and the tried and true—some trends
continued and there were a few surprises.
Suddenly, this year there was a lot
more attention being given to surround
sound level control for ATSC. The pending
legislation south of the border, threatening
penalties to those broadcasters
transmitting excessively loud commercials,
might have had a little something
to do this sudden interest.
Whatever the cause, there was lots of
new stuff and, dare I say it, many new
and creative approaches to tackling this
problem. Evertz, Harris and Miranda each
had their own unique take on it.
Dolby Labs surprised me—I had expected
that they would have something
to say about this—by introducing a multichannel
audio “processor” that doesn’t
and won’t work in real time. It works at
server ingest time or later, by examining
and treating the audio files on the server
and writing them back there. It also produces
all sorts of statistics on the audio it
treats, but it won’t work in real time so
it’s not of much use for live broadcasting
or for level control after the server.
Linear Acoustics took a more traditional
approach, and their box looked
more like an audio processor to those of
us that are used to looking at such things.
They and Harris also had novel new
graphical ways of displaying multichannel
audio (Harris actually had at least two
different displays on offer, one of their
own and one from dts, the digital theatre
sound people), but apparently none of
these displays phase information.
Lots of approaches; but it now remains
to be seen if any of them are particularly
effective. Impossible to tell while on the
exhibit floor.
There was a great deal of gabbery
about the new mobile 8VSB transmission
standard, and mobile ATSC. Pardon my
cynicism; it seemed like a lot of energy in
search of a market. Maybe I just need
someone to explain to me why we would
need all this. I will be the first to admit
that it is in the nature of the bleeding
edge to introduce all sorts of new ideas,
good and bad. In fairness, I also have to
admit that it is often in my nature to wonder
who would want a lot of this new
stuff, and if it really represents progress
in any real form.
On that merry note, there was much
discussion on the latest IBOC radio developments
as FCC announced that the requested
increase in injection levels for the
digital sidebands has been “somewhat”
approved. Whether the digital power can
be increased from the old level of 1% of
analogue (-20 dBc) to 10% (-10 dBc) is
dependent on each individual station’s
protection requirements—some can and
some can’t. Most can increase part way,
at least (perhaps -14 dBc).
A further submission to FCC would
allow unequal power levels for upper and
lower sidebands, so a station could really
squeeze out the last few allowable IBOC
watts on each. Just calculating the transmitter
power size requirements for a station
under the new and the proposed
rules is a major operation, best left to the
transmitter manufacturer.
As this whole IBOC business gets more
and more complex, and just refuses to
stay still, I’ve been thinking about how
lucky we are in Canada that we haven’t
had to deal with any of this just yet. Let’s
leave it to the U.S. broadcasters to keep
beating on this drum until the smoke
clears and a stable standard emerges.
Maybe, if they can get that far, maybe
then there will be something worthwhile
for Canadian broadcasters to look at—
hopefully without some of these costly
growing pains.
Speaking of the Excited States, there’s
another proposal that’s just been submitted
to FCC that would allow all U.S. AM
stations to increase power by 10 dB on
their day patterns, using the argument that
the protection requirements would stay
the same if everyone increased by the
same amount. It’s intended to help overcome
electrical interference problems.
Night time power levels would be unchanged.
But we’d be talking about AM
transmitter power levels up to 500 kW
per station! Yikes!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada JULY/AUGUST 2010

ENGINEERING
I remember the CAB
technical committee
BY DAN ROACH
Iwas saddened to hear of the
Canadian Association of Broadcasters
demise. I can still remember “back in
the day” when much of the CAB’s work
was indispensible.
Which isn’t to say that all stations
in Canada belonged to the association.
Smaller stations often found the dues to
be a hard pill to swallow; but whatever
station I was working at, member or nonmember,
that station did seem to benefit
from some of the good work being done
back at CAB headquarters. Stations universally
appreciated the effort; some were
not able to support the association directly
but they all wanted to.
At its best, it was work that helped
everyone in the industry not just a segment
of it.
In the mid-1970s, there was a move
afoot to change the spacing of AM channels
to 9 kHz instead of 10 kHz for North
America. And at first glance it seemed
there were some pretty good reasons to
do this, not the least of which was to
reduce night time interference coming in
from 9 kHz-spaced stations in the rest of
the world. It would also add a few channels
to the already-congested AM band,
for expansion and improvement (this
was seemingly ages before the AM band
extension took place).
Hold onto ’yer horses, I said at first
glance.
For high-power stations with directional
arrays, the 9 kHz transition would
have meant enormous, even crippling, expenditures.
By changing frequencies, the
locations of co-channel and adjacentchannel
stations, and hence the directions
that required RF protection, would
change completely. Suddenly your field
full of towers would need to be moved
all around, and new phasing and matching
circuits designed, built, installed and
tuned up to boot!
Even in the 1970s, we’re talking about
hundreds of thousands of dollars for each
radio station (at the very least) in order
to keep its operation essentially the same
as it was before the operation began. And
that presumes that your station already
had enough transmitter property available,
in the right shape, to accommodate
the new array. Otherwise, you might as
well start over with a new transmitter site
as well.
Astonishingly, the technical folks at
the National Association of Broadcasters
didn’t seem to realize the gravity of the
situation, and in the early stages of the
movement they actually supported the
transition to 9 kHz. It took a determined
effort from the CAB’s technical committee
members to rouse them and sound
the alarm. Then their united message filtered
through to the FCC and DOC, and
in the end the 9 kHz spacing proposal
failed to get approval at the next international
meeting of governments that
ruled the airwaves: the NARBA, or North
American Radio Broadcasting Agreement.
But it was a near thing.
Well, as they say, that was long ago
and far away. Unsung heroes of the CAB
Technical Committee, a defunct committee
of what is now a defunct organization,
toiled to prevent an industry-wide
catastrophe from taking place, on what
is now considered by many to be a secondary
broadcast band.
It all seems to be so far removed from
our world of broadcasting today.
Maybe you’ll have to take my word for
it, but this was a very big deal at the time.
Instead of crippling 90% of Canadian AM
radio overnight, we’ve seen a slow, general
decline in the fortunes of many AM
radio stations. Not that 10 kHz spacing is
responsible for any of that.
And although it was a benefit specifically
for AM broadcasters, the CAB was
able to act decisively in the interests of
the industry and realize a positive difference
for everyone concerned.
And that’s the way I want to remember
the Canadian Association of Broadcasters.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MAY/JUNE 2010 39

ENGINEERING
Monitoring surround sound
for broadcast, part 2
BY DAN ROACH
We ended up last time with the
start of the problem of graphically
monitoring 5.1 audio,
which needs absolute level display for
left, centre, right, left surround, right surround,
and low frequency channels. And
that’s just the start of the problem.
The figure below is a snapshot of
what the minds at Tektronix have come
up with, in conjunction with concepts
licensed from RTW, a German company
with their own multichannel audio display.
They have obviously given this problem
a great deal of thought!
The six bar graphs on the left of the
figure below show the peak levels of our
six discrete audio channels. The lissajouslooking
pentangle on the right is a representation
of the sound field that results.
The first five channels are all run
through an “A” weighting filter, which
simulates the audio response of the
human ear. Then RMS levels are calculated
and laid down with the origin in the
middle of the display, and the outer corners
are the maximum levels for left
front, right front, right surround and left
surround.
The outer edges of the display are at
full-scale digital level. There are fine
perpendicular lines each 10 dB. So the five
Figure 1: Tektronix surround-sound display.
points of the pentagram show the “shape”
of the sound field at this moment.
Tektronix next introduces the concept
of correlation, which is a different way to
express phase data between two channels,
completely stripped of level comparison.
Correlation is a number between +1 and
-1, where +1 represents identical phase
and content (mono), and -1 is opposite
phase and identical content (oops!). 0
correlation indicates no common content.
The bars around the sound field sides
show correlation between L/C, R/C, L/R,
R/Rs, L/Ls: The white tic marks indicate
the phantom source of each channel pair;
the length of the line a measure of the
“vagueness” of the phantom source. That
is, a short line shows a high correlation,
a long one shows a lower value.
The sides of the pentagram bulge out
or in to display positive or negative correlation.
More importantly, the colour
of the correlation bars changes with the
value: white for mono, green for normal
stereo, bright red for mostly out-of-phase.
As final touches, each of the channels
in the bar graphs is tested for clipping,
mute, silence or overlevel, and these alarm
conditions are printed over the relevant
bar if they exist. And a couple of additional
bar graphs are added on the right,
which can display
left and right total
(stereo output) or
Dolby promix information.
The centre
of the dominant
sound at any moment
is also calculated,
and displayed
as a white crosshair,
hopefully not too
far from the centre
of the display.
The result of all
this is a very dense
display with a lot of
information about
our sound data, but
which also offers some help to those that
can afford only a quick glance in the
form of colour coding for various suspected
alarm conditions. I’m guessing
that with continued exposure, the shape
of the sound field display alone would
alert the experienced eye that something
was amiss.
One thing is for certain—we have definitely
left the stage where we can use a
few VU meters to indicate what is acceptable
and what constitutes a problem with
surround sound.
And the need for some sort of graphical
interface is greater than ever, especially
since television control rooms are rarely
going to be equipped with surround
sound systems for listening, and most of
them nowadays are running multiple programs
at once in any event, so most likely
no-one’s listening to the audio at all.
I have only scratched the surface of the
Tektronix approach; interested readers
should visit the company’s website and
locate their application note, Monitoring
Surround Sound Audio.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada APRIL 2010

ENGINEERING
Monitoring surround
sound audio for broadcast
BY DAN ROACH
Many of us noted through the
NTSC era that the quality of
the audio always played second
fiddle to the pretty pictures. As a consequence,
so long as the sound channel
was more-or-less intelligible, 99% of the
effort and expense went into the video.
Surprisingly, it proved to be pretty easy
to manage one mono channel of audio.
Now that we’re entering the age of
ATSC, these audio problems, rather than
going away, are coming home to greet us,
but in a new, expanded, much more complex
form. It has become clear that any
workable solutions are going to require
new thinking as well.
So let’s look at what’s being bruited
about by the great minds just to be able
to monitor and detect ATSC audio problems.
Presumably detection will lead to
understanding and, eventually, correction!
The good news here is that we no
longer have to worry about deterioration
of audio through transport, dubbing and
transmission processes. The absolute
audio levels are now effectively set “at
the factory” in production, and shouldn’t
change unless we purposely adjust them.
The bad news is that in an environment
where the standards are left subjective,
audio from different sources is going
to lack consistency.
In the past, radio stations faced a similar
problem, which was often controlled
by limiting the “carting” of audio to only
a few staff that understood the problem
and practiced in-house discipline, to keep
levels and tightness the same from cart to
cart—in effect, they developed tighter inhouse
standards. That system broke down
when CDs came along, and music stopped
being carted before on-air use.
Level consistency did come back to
radio when audio once again had to be
“carted” into automation systems. And
was at least partially lost again with the
purchase of complete music libraries on
hard drive from vendors that lack those
tight in-house standards.
In the beginning, there was the VU
meter. For this discussion, I don’t think we
need to go farther back than the 1920s.
Carefully specified ballistics, that more or
less mimicked the human ear’s notion of
loudness, and two zones colourfully laid
out in black and red. You could give a new
operator a notion of correct operating level
by simply stating that they should keep
the needle from going into the red.
Intuitive and easy to understand; look
how long the VU meter has reigned supreme,
despite attempts to improve upon
it in the 1970s with the ill-fated PPM
meters that briefly became fashionable.
I think the main problem with the
PPM was that, once again, the reference
level and consequent use became subjective.
The meter’s response was tightly specified,
but there was not one obvious way
to use the meter. And there was more than
one PPM standard out there.
Mike Dorrough entered the scene with
a creative LED display that simultaneously
showed peak and VU levels, but it
certainly didn’t get the industry-wide acceptance
of the VU meter.
Then along came stereo, and suddenly
level control of two related channels
wasn’t enough—we had to keep an eye
on the phase relation between left and
right as well. The classic way to do this
was with an oscilloscope lissajous figure,
with left driving horizontal and right vertical.
L+R represented by a +45 degree
line, and L-R by the -45 degree axis.
Some folks (notably Tektronix) rotated
the whole display by 45 degrees, so
now you had a sort of view of the sound
field, with L+R forward and back, and L-
R left to right. Which was a bit better.
But while the lissajous remained the
standard viewer for phase information, it
didn’t really catch on with studios or
broadcasters. Not like the VU meter.
Today’s ATSC supports Surround 5.1
audio, which increases the demands for
monitoring many fold. First of all, we
need to monitor left, right, centre, left
surround and right surround channels,
and the low frequency channel. Then we
need to keep an eye on the relationships
between them. And, as we’ll see, there’s
even more than that.
Our VU meters just aren’t going to
cut it for this problem!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached at dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MARCH 2010

ENGINEERING
Form C Contacts:
Very dry, shaken, not stirred
BY DAN ROACH
One of the phrases we’ve all been
using for years, passed down as
lore through the generations of
broadcast technicians, is the expression
“Form C Contacts”. Like so many of these
expressions, I’ll bet you know from experience
exactly what it means; but probably
not whence it came nor the context.
When specifying relays and switches,
Form A Contacts were another way of
saying “single pole single throw, normally
open”. I guess Form A says it quicker.
Form B is the same as A, only normally
closed (when in the rest or un-energized
or unlatched position). The ubiquitous
Form C is “single pole double throw,
break-before-make”.
Form D is the same as C, except it’s
make-before-break. When audio consoles
used telephone keys as switches, this was
a popular type of switch to use to turn
channels on and off.
Those four types of switching are pretty
common, and as we have seen the Form
designation allows a precise shorthand
description. Of course the powers that be
then tried to screw things up by giving us
too much of a good thing and so filled up
the whole alphabet, and more, with all
sorts of exotic switching combinations.
As a result, no-one remembers what
they are (if they ever knew, of course),
and if you walk into your switch vendor’s
establishment and ask for a Form K
switch, I guarantee that they won’t have
any idea that you want a single pole double
throw switch with a centre off position.
Really, the only Form that you can
use with impunity in public today is Form
C, and I suspect that it may disappear as
well one day. Which is a pity, because I’d
much rather say Form C than “single-pole,
double-throw, break-before-make”.
Often when an equipment manual
specifies a Form C output for a device, it
will go on to state that they’re dry contacts.
Of course, in electrical parlance
this means that there’s no “juice,” or
electricity, applied. When referring to telephone
broadcast pairs, a dry or metallic
pair was one that had no foreign battery
(ignoring the fact that all pairs are, of
course, metallic). What was meant was
that the pair was contiguous copper from
one end to the other, without any carrier
or fibre channel sections in the middle.
Today, a metallic pair is a very rare
bird indeed. A previous generation of telco
and broadcast engineers called these
dedicated broadcast lines NEMOs because
they were Not Emanating from Master
Operations. But that’s all ancient history.
Switch and relay contacts are often
made of silver, since it’s fairly common
and an excellent conductor. If the silver
oxidizes that’s okay, because silver oxide
conducts very well, too.
But eventually sulphur compounds in
the atmosphere can cause a skin of silver
sulphide to form on our contacts and
form an insulating layer. If there’s DC being
switched by the contacts, microscopic
arcing will occur that’s enough to pierce
the skin, and we’re back in business.
But this is a real problem for dry contacts,
which to relay makers are those
switching less than 1mA or 100mV.
Manufacturers’ solutions include wiping
contacts that rub back and forth to break
the sulphide layer as they make and break
the circuit, bifurcated (forked) contacts
that improve reliability by doubling up
(redundancy), gold flashed and gold-palladium
contacts that are resistant to corrosion,
and gas-filled relays that are filled
with dry nitrogen gas before sealing.
Mercury-wetted reed relays were supposed
to be the ultimate answer to this
problem, but that didn’t work out too well
and they’ve pretty much disappeared from
the scene at this point. Of course, even
those mercury-wetted contacts were still
dry contacts, but that’s another story!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver.
He may be reached by e-mail at
dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada FEBRUARY 2010

ENGINEERING
Imay have seen the future, and it might
be called RT+.
This column is for anyone that laments
the loss of DAB and its promise of
“interactive radio”; that thinks the future
of radio is compromised by the Internet;
that radio has been doomed by the iPod;
or that just wants to play with radio
broadcast technology at the cutting edge,
but doesn’t have a whole potful of money
to spare for that purpose.
We’ve talked before about how RDS/
RBDS, that 25-year-old European technology,
offers many interesting features, and
how it can be implemented with little effort
on the broadcaster’s part. I’ve always
admitted it could get expensive if you let
your imagination run free, but let’s face
it, you can get started for much less than
a kilobuck, which is pretty negligible in
today’s broadcast equipment world.
Why, curiously, is it already implemented
in lots and lots of cars, but you’ll
be hard-pressed to find even one aftermarket
car radio that has RDS? Why is this
feature present in Europe, but hard to get
a handle on here?
Well, the folks that brought you RDS
and RDBS have created a subset of that
technology called Radiotext+ (RT+), and it
just might set music radio on its collective
ear. The latest versions of the iPod nano
(the models that include an FM tuner) are
already equipped for it, and so is every
model of Microsoft’s Zune player.
It’s really simple, but quite elegant.
Tag, you’re it!
BY DAN ROACH
RT+ inserts control codes in the littleused
Radiotext part of RDS which will
allow identified subfields inside Radiotext.
So you can insert playlist information, just
like with old RDS, but now the receiver
can tell which text is the song title and
which is the artist. More importantly, you
can insert song ID information (supertagging)
which the iPod can remember
and which iTunes will later recognize and
allow your listener to select for purchase,
if they hear something they like.
More importantly than that, Apple
will know that the information came from
your station, and might even pay you a
commission for helping this whole process
along—participating U.S. stations are
getting 5% of each sale… this from what
is now the world’s largest music store.
Most of us in broadcasting have long
contended that radio is the music company’s
best friend; that it introduces listeners
to the music that they didn’t know
they wanted to hear and that it causes
music to be bought and sold. RT+ just
might prove that point.
Okay, you’ve heard me prattle on
about something similar at some length
when discussing IBOC. I still think it’s a
killer application, but when’s the last time
you saw anything IBOC happening around
here? This application has been lifted
wholesale from the IBOC bag of tricks
and placed on regular FM. It’s here right
now and already implemented in that
notorious radio-killer, the Apple iPod.
Now, here come the caveats:
RT+ is here right now. Software to program
your playlists into RT+ is here right
now. You can get your playlists into your
listeners’ iPods right now. No doubt you
can start “super-tagging” right now, but
iTunes Canada doesn’t yet support it so
you won’t start getting those cheques for
sales commissions this month—Apple
has implemented it only in the U.S. so
far. But I wouldn’t bet against it arriving
real soon, especially if you start bugging
them and indicating that your station is
interested.
In the meantime, there are all those
other field identifiers. With RDBS and
RT+, you could be sending ski reports,
weather information, teasers about what’s
coming up on the station in the next few
minutes, very short news bulletins and
road reports—anything you can think of.
The only limitations are your imagination,
and just how much effort you want to
pour into something that’s so brand new.
Look for more information on tagging
and Apple’s partnerships with U.S. broadcasters
on the Apple iPod U.S. website.
Descriptions of the RT+ enhancements
are freely available on the Internet, or
in the manuals of the very latest RDBS
encoders.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver.
He may be reached by e-mail at
dan@broadcasttechnical.com.
62 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada DECEMBER 2009/JANUARY 2010

ENGINEERING
Grrr!! Attack of the angry engineer!
BY DAN ROACH
Sometimes people can be so offtrack
that you just want to smack
them on the side of the head. I felt
that way a little while ago when I read a
column in this very magazine claiming
that Radio Is Dead.
Like a sucker I read on, and thus gave
this article more attention than it deserved.
And I found myself getting hopping
mad, disagreeing with just about
everything I read. But in the end it turned
out to be just another piece of sloppy writing,
contrived to generate reaction but not
too logically assembled.
It’s the age-old problem of careless use
of everyday words. The writer’s argument,
once all the dust settled, seems to be
that “radio” is dead, but “broadcasting”
will live on. Suddenly, from controversial
statement his premise has decomposed
into “well, duh”.
And even that’s only because of the
narrow way he uses radio.
If the author argues that the little fivetransistor
AM pocket radio from the 60s
is gone, well in a sense it is. But whether
you’re using one of those, or an iPhone©,
or an Internet radio, I’d argue that it’s still
a friggin’ radio.
Radio is NOT dead! It is just mutating
(perhaps) into yet another form, just
as AM has been dislodged by FM and
mono by stereo. After all, whether the
music industry is flogging Edison cylinders,
or LPs, or eight-track cartridges or
CDs, or MP3 files, we still call it music!
So it turned out to be all about the fuzzy
use of words.
There was some disinformation about
call letters being irrelevant on the net.
What drivel! Most “real” radio stations
don’t use call letters in the legal sense,
and many haven’t for decades. But some
sort of catchy shorthand mnemonic marker
is necessary to separate your program
from others, and whether it’s your call letters,
or your frequency, or your IP address,
or your slogan, once again—WHO
CARES? It amounts to the same thing.
And there was some crap about
water-powered cars, and irrelevant transmitters
being sold for scrap. In all of this,
the important point was, sadly, missed—
radio, as a medium, faces challenges today,
mostly financial. The essential thing
that makes modern radio—the one-toone
communication of relevant (especially
local) entertainment or information to
the listener in real time as, or even before,
she even realizes she needs it or wants it
—that connection is every bit as magical
and relevant as it was in Fessenden’s day.
The burning issue today ought to be
how do we produce great radio consistently
in today’s world? In this case, the
medium is not the message—the message
is the message.
❖❖❖❖❖
Lately I’ve been trying to wean myself
from using the word “redundant.” I am
making this conscious effort because all
around me people in the broadcast industry
are receiving pink slips, and often they
are being described with this word at
more-or-less the same time. After awhile
you just don’t want to hear the word anymore,
even though it’s a perfectly good
word.
This underscores the fact that on the
technical side we use this word a little bit
differently, or perhaps more accurately. We
view the concept of redundancy from the
side opposite that of management. One
person’s reliability, it seems, is another
person’s waste.
Maybe it’s better to use the phrase “single
point of failure”. Nobody likes that,
of course, it’s got “failure” written all over
it. But it’s the same thing.
In engineering, redundancy is a good
thing, and we strive for it. But not when
there are accountants listening, of course.
And I’m hoping never to hear anyone
at a broadcast station referred to as a “single
point of failure.”
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver.
He may be reached by e-mail at
dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada NOVEMBER 2009

ENGINEERING
A cure for voltaic piles rediscovered!
BY DAN ROACH
Every time I see a UPS fail I’m reminded
how much collective knowledge
we are losing, week by week
and month by month. While there have
been many exciting developments in batteries
in the last few years, I sometimes
think we’re losing ground faster than we
are gaining.
Why so glum? Maybe 95% of UPS failures
are due to the drying out of the rechargeable
gel cell inside. Now, while gel
cells are convenient in the sense that they
hardly ever leak sulphuric acid all over the
place, their lifetime is so short that they
should come with a best before sticker.
Any gel cell with more than two years
service is on borrowed time; more than
four years and still working is almost a
miracle. So how could we do better?
A gel cell is essentially a semi-sealed
car battery with jellied electrolyte. The
good news about car batteries is that you
can sometimes add water to them to extend
their life. The bad news is that, like
the gel cell, they have a built-in failure
mechanism to make sure you keep trudging
back to the battery store every few
years.
In the chemistry lab we’re taught that
the main components in the car battery
are sulphuric acid and two lead plates.
Ah, but the devil, as they say, is in the
details.
You see, if car battery plates were pure
lead they’d be so heavy and malleable
that they’d soon bend, sag and short out
of their own weight. So a little antimony
is added, which stiffens them up just fine.
But that is also why the battery wears out
in the end. The trace amounts of antimony
leach out into the electrolyte and poison
the chemical reaction that we want.
And the battery gets thrown on the scrapheap.
So here we come to the tragic part of
the story. Would you be surprised to learn
that more than 60 years ago, the Bell folks
invented a rechargeable battery that needed
watering only once a year, and that
would last 100 years or more in UPS service
with only minimal maintenance? That
is the story of the lead-calcium battery.
Telcos uses a lot of batteries. The telephone
system famously runs on its own
48 VDC supply. AC power supplies and
motor generators supply most of the power.
But the telco folks float batteries on
the line to filter the supply, and deal with
power transients and AC mains blackouts.
They also help regulate the main power
supplies.
It didn’t take very long for telephone
maintenance crews to get very tired of
servicing regular batteries. So, in the 1950s,
they developed what is now called the
lead-calcium battery.
It resembles a car battery, but is often
housed in a clear tub so that you can
look inside. The voltage is ever so slightly
less than a car battery. It’s not meant
for a lot of deep cycling, but rather to be
floated at full charge 99.9% of the time.
But the electrolyte doesn’t keep evaporating,
and it lasts almost forever—by
most estimates 100 years or more. These
batteries are still often seen where battery
float banks are established, and they’re
still available and only a little more expensive
than a good car battery—and you
only buy them once!
If it’s any consolation, even the engineers
at telcos seem to have forgotten
about the benefits of the lead-calcium
battery.
A couple of years ago, we experienced
a whole series of puzzling telephone company
outages that took our brave telephone
crews a very long time to correct.
It turned out that this relatively new (two
to three years) installation included—wait
for it—gel cells in the power supply. And
of course they had dried out and failed,
intermittently, to filter the central office
power supply. The resulting instability and
supply bounce played ruddy hell with
everything from the microwave radios
to the multiplexer—and everything else
besides.
The phone company had forgotten
their own lesson, and the prime rule of
troubleshooting anything electronic.
It’s always the power supply.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver.
He may be reached by e-mail at
dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada OCTOBER 2009

ENGINEERING
The air is humid; to be cool, divine!
BY DAN ROACH
There’s a significant delay between
when I put these notions to paper
and when they arrive in your lap.
As I write this, we’re deep in the dog days
of summer and slowly melting. It’s so hot
out that… well, you can use your imagination
to fill in the blanks.
Modern transmitting equipment is dependent
upon a continuous ample supply
of clean cooling air for its continued
operation. This has always been true, but
today it is more critical than ever. There
is a tendency to neglect the solid-state
transmitter site… while the tuning and
tweaking style of maintenance is now
much less, the routine maintenance of
air-handling equipment remains of paramount
importance.
Inaway,mostofCanadaiscursed
with a temperate climate. Where things
are really hot, transmitter sites often are
outfitted with air conditioning which
certainly can keep things more stable
and a lot cleaner inside the building. Of
course, it also gives us something else
that can break and cause trouble.
In any event, most of us in Canada
have to make do with whatever fresh air
Mother Nature sees fit to provide. And
that can be variable in temperature,
humidity and cleanliness.
Good air filters can help a lot but
selection depends upon the types of particulates
you have to filter out. Pollen, for
instance, can be much easier to remove
than the fine soot and dust that comes
from cars and traffic. With sites getting
fewer and fewer visits for routine maintenance,
it’s especially important to keep
alert to unusual conditions that might accelerate
filter wear—two examples might
be construction happening near the site
(lots of dust), or forest fires in the vicinity
(smoke and ash). A plugged-up air
filter is even worse than no filter at all, if
that’s possible!
One problem unique to our coastline
sites is salt content in the air. It accelerates
corrosion of anything metallic. Even
“stainless” steel!
Motor bearings need to be checked
from time to time. Sleeve bearings, lubricated
regularly, can last almost forever.
Ball bearings don’t need routine lubrication
but they will wear out. V-belts need
regular inspection and replacement.
Always be careful when directly connecting
ducts to either the intake or
exhaust of a transmitter. Firstly, without
assistance the ducts will always add resistance
to the flow of air and the transmitter
designers did not take this into account.
You’ll need to add helpers in the form of
external blowers or fans and some sort of
system to shut down the transmitter if the
helper fan fails. Be careful that your air
system doesn’t defeat the internal transmitter
air flow failure detection. And don’t
fall into the trap of equating air pressure
with moving air volume.
Sept 17–20, 2009
at Horseshoe Resort just
north of Barrie.
Contact Joanne Firminger
for details at
1-800-481-4649.
www.ccbe.ca
Always remember that with these
mechanical devices it’s not a matter of
“if” they’ll fail, but “when”—whether it’s
a burned-out motor, a tripped circuit
breaker, or a broken V-belt. And you must
anticipate how the transmitter will react
to all these types of failures. Many transmitters
have been burned up beyond
repair by one or another of these simple
malfunctions.
All in all, it’s generally safer, but not as
quiet, to loosely couple any ducting to the
transmitter intake and exhaust. That way,
the transmitter and building systems operate
independently and there are fewer
surprises.
Another good notion is to supplement
the building air handling system with a
separate one that normally seldom gets
used. This can be as simple as an extra
exhaust fan with a separate thermostat.
If the main system fails, the secondary
system will at least keep things tolerable
inside until repairs can be completed.
Of course, the secondary system
should be powered by a different circuit
from the main.
Remember, in everything from air handling
to IT we must always avoid the single
point of failure.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver. He
may be reached by e-mail at
dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada SEPTEMBER 2009

ENGINEERING
Ruminating on the DTV rollout
BY DAN ROACH
This month’s column is a bit of a departure for me. Normally I try and avoid the
political issues, I figure the folks in the rest of the magazine can deal with that
kind of stuff so much better than I can.
But there are a number of changes due to the impending DTV conversion in Canada
that have some of us technicians wondering what the heck’s going on. And I’ve heard
from some broadcast managers who are wondering the same thing.
As workers in the broadcast industry, here are some things I think we should be
seeking answers to. I’m not pretending to be an authority on these issues, or to have
all the answers—I’m more of a curious bystander. Let’s just say that these are questions
that, if I had the ear of the CRTC and Industry Canada for a few minutes, I’d
being asking:
1) What’s the deal with CBC’s plan to shut down all their TV transmitters outside of
the major markets?
The CBC might have unilaterally decided that off-air TV reception is obsolete,
and expensive, and inconvenient, but it’s still a condition of licence. Their decision
is especially poignant when the rest of us are faced with these expensive DTV
upgrades.
When I first heard of this plan I thought it was just an attempt to solicit extra
funding, as with the CBC Accelerated Coverage Plan in the mid-1970s. However,
the months and years have gone by and so far I haven’t heard any response from
officialdom, either in support of or against the CBC plan.
I have heard from several folks that aren’t worked up about it at all, but to me it
seems (a) unfair to other broadcasters and (b) a decision that is properly way
above the CBC board’s pay grade. Isn’t it their mandate to provide this service?
Isn’t it part of the reason for their annual subsidy?
2) By the time you read this we’ll be down to little more than two years before the end
of the line for analogue television (August 31, 2011).
The last system-wide upgrade I can remember was the advent of BTSC stereo, and
at that time the potential loss of simultaneous substitution rights with the local
cablecos was a very effective stick to spur on the rapid adoption of the new technology.
(The argument was that cable companies could refuse to substitute a stereo
U.S. transmission with a mono Canadian one, due to technical inferiority. Whether
or not this actually ever happened, the possibility that it could was enough to get
many broadcasters spending. Like DTV, BTSC was a costly technical upgrade that
offered no new revenue to the broadcaster).
Using the same logic, presumably the cable companies could refuse to substitute
analogue Canadian signals over U.S. DTV ones. Is this as worrisome to broadcasters
this time around? Or is it completely swamped by the fee-for-carriage
issue?
3) While we’re on the subject of the cable companies, I’ve already heard grumbles
from DTV broadcasters about the lack of signal quality once their HDTV signals
spill out at the far end of the cable.
We’ll all be delivering just shy of 20 Mb/second to the transmitter, but there
don’t seem to be any regulated standards for the cable companies to follow suit.
It’s ironic that in the early days of cable TV, the service was very much about technical
quality. Perhaps this latest issue underscores that today the number of services
offered is more important than picture quality. Perhaps it shows how valuable
bandwidth has become in the cable universe.
Either way, it still seems (to me at
least) to be unfair to the subscriber
and a disservice to the broadcaster to
crunch down a product that so many
have spent so much effort and money
to improve into something altogether
lesser.
Who ever heard of subscribers putting
up rabbit ears to improve their reception
quality?
At this point, having most likely offended
just about everybody, I’ll put on
my hardhat and recede into the distance.
To those who disagree with me, please
do take the time to explain your point of
view. I think we’re all seeking some
answers right now.
I promise next time to focus on something
less topical and more technical.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver. He
may be reached by e-mail at
dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada JULY/AUGUST 2009

ENGINEERING
Random thoughts from NAB 2009
BY DAN ROACH
Fresh from the NAB annual broadcast equipment swap meet and fair, with a few
impressions.
This year, of course, attendance was way, way down. NAB claimed that there were
88,000 attendees and, as always, there are some of us who think that even that figure
is probably well inflated. Certainly there were fewer visitors than in the heady pre-
9/11 days when NAB used to claim numbers around 140,000 or so.
I didn’t believe them then, either.
Lower attendance in of itself is not a bad thing. With the ranks thinned, the
exhibitors become more accessible and it becomes possible to have a conversation
with an exhibitor without having to make an appointment weeks in advance.
And, with the reduced numbers the hyper-inflated cost of NAB week in Vegas gets
reduced as well. This allowed me to take an extra day and attend the annual Nautel
Users Group meeting, or NUG. I found this three-hour session to be very valuable.
As I’ve mentioned in past columns, Nautel wrote the book on lightning protection
techniques at transmitter sites, and this year they featured a presentation by their
Chief Engineer Emeritus, John Pinks, reviewing and updating his classic work on the
subject. As he pointed out, anyone wishing to market a transmitter that connects FET
transistors to the end of a several-hundred-foot tall lightning rod faced an uphill battle
when trying to convince traditional tube-type station engineers. What was once
almost scandalous has now become commonplace. Some of Pinks’ notions are common
sense, but many are counterintuitive, and all are underscored by many, many
years of study of this problem.
Kevin Rodgers surprised me with a “maintenance tips and tricks” run-through,
covering virtually every model of transmitter Nautel has made. There was a time when
Nautel was not so outgoing with this type of information, and it’s really encouraging
to see that they have had a change of heart.
I’ve been assured that these items are available on their website to any and all, so
feel free to avail yourself of their generosity and have a look for yourself!
❖❖❖❖❖
The continuing evolution of computers for programming radio, and the pending
marriage of these systems with BBM’s PPMs will have a number of interesting and perhaps
industry-shaking consequences. Ross Langbell of RCS Canada ran me through
some of the technology out there at the bleeding edge. For a station technician like
me, this is humbling stuff indeed, but it is obvious that some great minds have been
putting a lot of thought into applications for the “metrics” of radio.
First, the music scheduling programs I have seen heretofore basically operate by
filling programming slots with the first selection that meets the required criteria.
Instead, the new RCS scheduler will examine every possible selection in the library
and choose the one element with the highest score… the best element.
Second, monitoring services, where available, are already noting every selection
and every commercial aired, minute by minute, by every station in a market. This data
can be mined, either to show which commercial buys are going where, or perhaps
where they aren’t.
And program repetitions, combined with PPM data, can be used to (partially)
overcome the resolution vs. accuracy problem noted by Jeff Vidler in his analysis in
the April issue of Broadcast Dialogue (PPM Info: Too much of a good thing?), producing
the result that we’ve all been dreading (or wishing for): a graph showing bumps,
up and down, that occur in our audience measurement whenever a given announcer
or program element goes to air.
I leave it to your imagination what
will likely happen to an announcer or a
song that predictably produces a “down
bump” in audience measure. A little further
massaging and we can even tell to
which stations our listeners go when
they punch out.
This is all just a little too much for
someone who remembers when the jocks
were allowed to pick the music that was
played on the station. And trust me;
most of them weren’t using mathematical
algorithms to choose the next song.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver.
He may be reached by e-mail at
dan@broadcasttechnical.com.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada JUNE 2009

ENGINEERING
Circuit breakers, power factor
and back e.m.f: Things your mama
never taught you
BY DAN ROACH
This month we have a grab bag of little items picked up at
various transmitter sites over the years, some at personal
expense. But they’re offered to you gratis…
Circuit breakers: When well chosen, they’re a boon to the
industry. When not, well, they can be a pain in the you-knowwhat.
Industrial circuit breakers used at transmitter sites have both
a thermal and a magnetic component. The thermal trip-point
is supposed to match the “ampacity” stamped on the breaker,
with a slow response-time like a slow-blowing fuse. Leave it to
electricians to come up with a new silly-sounding-and-yetunnecessary
word: what was wrong with amperage?
The magnetic trip-point is five to 10 times higher, but with
a quick response time. On the nicer units, the magnetic trippoint
can be adjusted in the field.
For transmitter connections, beware of circuit breakers meant
for general lighting loads as their magnetic trip-point may be
lower, and not adjustable. Whether it’s for charging power supply
capacitors, or starting up big blower motors, many transmitters
require a good boost to get started.
Sizing of breakers for transmitters can be a bit of an art form.
Some transmitter manufacturers are quite helpful, others not
so much. Not many will tell you about appropriate breaker sizing
when the transmitter is running at less than 100% power—
which, of course, is quite common.
Power consumption never drops in proportion to transmitter
power output, overhead for blowers, drivers and bias circuits, at
least. But that goes at least double for television transmitters,
which will use a lot of power just biasing power-stage transistors
to act in linear fashion.
And remember that current per phase for a three-phase balanced
load equals total VA divided by line voltage divided by
the square root of three!
Power factor is just your power company’s name for the
reactance of your load and, in our world, it is always inductive
and it is always caused by large motors.
A power factor of 1.00 has no reactance at all and is ideal,
and thus is never seen. As the inductance increases the power
factor drops, and below 0.90 or so the power company will
start charging you extra for the privilege of loading them down.
The cure is to place capacitors on the line to compensate for the
inductance.
Generally, the savings from the power company will more
than pay for the capacitor installation. When you install the
capacitors make sure to put them on their own disconnect, so
that you can service them with the rest of the site power uninterrupted.
Ditto for any surge suppressors you install at the site!
Back e.m.f comes from any big motors that are rotating.
It can give you a lot of grief if your emergency generator
panel switches quickly between normal and emergency positions
without first synchronizing phase between hydro and generator.
The result can be a sudden power transient as the motor
load and power supply try to quickly sync up, and can result in
random tripping of circuit breakers, blowing up of generator
exciter diodes and routine power line surge-related havoc.
What’s particularly insidious about this type of trouble is
that it won’t show up every time there is a transfer, as the size
of the transient will be related to the relative phase between the
two sources, so it appears as a more or less random event.
The cure for all this is an inexpensive add-on feature to your
generator transfer switch called delay-on-neutral. It ensures that
the power stored in the motor load is allowed to decay for a few
seconds before re-application of mains.
Dan Roach works at S.W. Davis Broadcast Technical Services Ltd., a
contract engineering firm based in Vancouver. He may be reached by
e-mail at dan@broadcasttechnical.com.
BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MAY 2009

ENGINEERING
Serial interface survival guide
BY DAN ROACH
Alright, I guess that was just about enough whining about
the troubles of interconnecting various equipment using
RS-232C. It’s a month later and our devices aren’t working
any better than they were when we started. So down to
business.
I mentioned last time that the pins are properly named
from the point of view of the DTE, which is usually the computer
or terminal, and usually is equipped with a MALE connector.
If the machine you’re connecting to it is a printer or
modem, it might have a matching FEMALE connector, perhaps
indicating that it’s acting as a DCE.
If both connectors are DB-25s, or both DB-9s, you might just
get everything working by using a premade straight-through
cable. Or you could try a few of the readily available adaptors.
If none of that works, you’re going to have to get more creative.
In the following text, all pin numbers refer to DB-25 connections.
Somewhere below, you’ll find a listing for equivalent
DB-9 pins for devices that conform to the standard (ahem, no,
there’s no prize for finding non-conforming machines!).
DB25 PIN ACRONYM DESCRIPTION DTE I/O DB9 PIN
2 TXD Transmitted data O 3
3 RXD Received data I 2
4 RTS Request to send O 7
5 CTS Clear to send I 8
6 DSR Data set ready I 6
7 SG Signal ground 5
8 DCD Data carrier detect I 1
20 DTR Data terminal ready O 4
Figure 1. RS-232C commonly used pins, from the DTE perspective.
In one respect things are easier now than in olden times, in
that many modern devices don’t use the handshake lines at all.
If this is the case, you can sometimes get by with a ground connection
(pin 7) and data from pin 2 to 2 and 3 to 3 or 2 to 3
and 3 to 2. If that doesn’t work, it’s time to try some tricks.
I mentioned that RS-232C is a NRZ, or non-return to zero
format. On the data lines, a 1 (mark) is represented by -9V and
a 0 (space) by +9V. The data lines, when they’re not busy talking,
will always mark time (-9V). All handshake lines assert at
+9V and negate at -9V. So if you look at a pin’s voltage level on
an oscilloscope, if it’s at 0V it’s either an input pin or there is
no connection to it.
By seeing which pins are asserted, you can get a clue as to
the pinout of the device. By asserting the common handshake
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcast
technical.com.
lines, you should be able to get some
action. The common handshake pins are
4, 5, 6, 8 and 20. A brute force approach
is to connect all these lines together from
both devices and connect a +9V battery
lead (related to pin 7 ground) to the
bunch.
If you get some joy this way, the next
step is to try and get rid of the battery.
Often this can be accomplished by finding
an asserted handshake line and just
jumpering to its associated line at each
end: 4 to 5 and 6 to 20 at each end of the
cable.
I mentioned last month that the evil
pin 8 is sometimes used as a “go to sleep”
pin for the whole interface, so sometimes
it needs to be connected to one of the 4-
5 or 6-20 jumpers to make sure it’s asserted
too.
One handy gadget you can easily justify
if you find yourself wrestling with
these problems fairly often is a breakout
box. This device has convenient pins and
plugs for test jumpering, and often LEDs
to indicate line status to see which pins
are active.
It can save you a lot of time and trouble
trying to figure out which flavour of
RS-232 interface you’ll be preparing today.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada APRIL 2009

ENGINEERING
Confessions of a
serial interface killer
BY DAN ROACH
Ijust HATE RS-232 connections. There,
I’ve said it and I feel better for having
said it. You probably want to say it, too.
I loathe everything about them—the
connectors and mounting hardware, the
seemingly arbitrary pin assignments and
most of the philosophy behind their design.
Sometimes I think that the world
would be a better place if RS-232 was just
expunged from the planet. But even then,
I’m sure that there would still be RS-232
devices in spacecraft, darkening the days
of technical spacefarers everywhere.
This interface sucks, and has sucked
for a long time, and yet we’re still surrounded
by machines that require it
to function. Sure, other serial interfaces
have come along, and we’re gradually
seeing USB-1, USB-2, PS/2, Firewire, and
Ethernet—in TCP/IP flavours and otherwise—coming
onto the scene. And they
all seem to work better than RS-232.
But the RS-232 connection remains
more-or-less ubiquitous, and so long as
that’s true it’s for certain sure that you’re
going to have problems with it. Forget
about plug-and-play, this interface wants
plug-and-PRAY!
RS-232 started out innocently enough,
as an interface between computer terminals
and modems. The terminals were designated
DTE (Data Terminal Equipment)
and the modems DCE (Data Communications
Equipment). We could quibble over
the selection of two such similar-sounding
names, but as it turned out there were
many more things that could, and did
and do, go wrong.
We could also complain about a 25-
wire interface that actually sends data on
only one or two wires, and, in 99% of cases,
only even uses half a dozen, but it’s a
little late for that now. We could whine
about the choice of connectors and hardware,
as it’s difficult to imagine a worse
bunch when you’re reaching around the
back of a machine in the dark under a
desk trying to make a connection, but I
guess that’s all water under the bridge.
Used between terminals and modems,
things still looked fairly straightforward
—but remember, this was just the beginning.
Along came computer mice, and
tablets, and touchscreens and printers and
plotters, and CD jukeboxes, and robotic
camera pan/tilt heads, and zoom lenses
and what-have-you. And then there was
the problem of connecting two terminals
to each other: which would be DTE and
which would play the role of DCE?
So while the standards organizations
stood on the sidelines, manufacturers kinda,
sorta worked things out for themselves—with
the result that almost every
connection becomes a new adventure.
About the only detail that one can like
about RS-232 is the relatively robust family
of line drivers and receivers in use,
Dan Roach works
at S.W. Davis
Broadcast
Technical Services
Ltd., a contract
engineering firm
based in Vancouver.
He may be reached
by e-mail at dan@
broadcasttechnical.
com.
and the fact that it’s a NRZ (non-return
to zero) standard so it’s possible to discriminate
between unused pins and pins
that are in use but inactive… there’s a
voltage that can be measured there.
And if you do accidentally short-circuit
opposing drive pins together, there
shouldn’t be any smoke released!
The main problem with the RS-232
standard is that it is not standard, at least
in the hands of equipment makers. It’s
more a set of general guidelines, observed
or not at the convenience of the designer.
DTE usually has male connectors, and
DCE female, but not always by any means.
Most often the connectors are DB-25,
unless they’re not: they might be DB-9,
or something completely different.
Then there’s the whole issue of handshaking
and flow control: in hardware or
software, and which of several methods?
And if two devices are talking, one device’s
transmitted data is the other’s
received data, and vice versa.
Baud rate? Who mentioned baud rate?
And parity? And even the number of data
and stop bits? Even if the arbitrary use
(or neglect) of handshaking pins doesn’t
get you, the sheer number of combinations
of data rate, parity and stop bits is
likely to fill your days. And watch out for
the DCD (data carrier detect) pin, which
might or might not put the whole interface
“to sleep” if it is not valid.
Yes, the RS-232 interface seems to have
been designed for maximum annoyance
factor. But if you ever start to think that
you’ve got it mastered, there’s always RS-
422 and RS-423.
38 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MARCH 2009

ENGINEERING
Blast those transmitter varmints!
BY DAN ROACH
At this time of year I often will write
a column about preparing your
transmitter site for the onset of
winter, but lately I’m preoccupied with
unkind thoughts towards those twolegged
vermin that choose to frequent
transmitter sites at odd hours and do
bad things to them.
There are three basic categories of
these miscreants: vandals and thieves and
arsonists, oh my! A pox upon them all!
The recent explosive rise in commodity
prices has suddenly made the transmitter
site an attractive and handy spot
to drop by and pick up any loose pieces
of metal, particularly aluminum and copper,
to trade for spare change. Lately it
looks like we might get some price relief
on the metals, but I suspect the learned
behaviour of these varmints will continue
regardless. And unfortunately, there are
often many bits of metal lying around,
or at least visible to the casual eye.
A common victim is the ground strap
and ground wiring used at the base of a
tower. This is often relatively unprotected—and
very visible. It’s a good precaution
to paint any exposed copper with
normal drab grey paint. This makes the
metal less shiny and so less likely to draw
the eye, and there’s always the chance
that the metal thief won’t recognize that
grey metal is copper.
Finally, painted copper increases the
(faint) hope that the metal can be identified
if the police should stumble upon
a cache. While you don’t want the metal
back, unless its source can be identified,
police otherwise have a hard time punishing
the troublemakers.
It shouldn’t be necessary to mention
that any loose bits of transmission line,
just like ladders and other aids to access,
should not be in plain view and should
be locked up inside somewhere.
Out here in B.C. our early experiences
with digital program lines often involved
T1 spans installed by Telus. These circuits
had so many growing pains that it became
common practice to place a spare
transmitter key inside a lock box at the
transmitter site, so Telus staff could come
and repair circuits without station staff
attending.
Years have gone by, and Telus long
ago stopped visiting without an invitation,
but the lock boxes remain, now long
forgotten by everyone concerned. But you
guessed it, metal thieves have been targeting
those lock boxes, and smashing
them for the keys inside, which often
still are operational.
Today’s thieves are well-organized,
often using all-terrain vehicles to get access
to remote sites, and frequently taking
only metals that are not part of operating
machinery—for instance the heavy
wires from the standby generator to the
transfer switch—so that their presence is
not immediately tipped off by a transmitter
failure.
The standby generator itself can make
an attractive target, even with the amount
of effort necessary to open it and remove
the windings. I called a generator service
company to arrange a repair after one
such unsuccessful attempt, only to learn
that the night before another bandit had
visited the generator company and stolen
one of their trailer generators and a truck
to tow it with.
That chain-link fence around your
compound isn’t really much of a deterrent.
Aside from the obvious weakness
to wire cutters, anyone with a pair of pliers
and half an hour can usually open up
the main gate. And the large ventilation
hoods and ducts at many transmitter
buildings can provide easy access to the
treasure inside, no matter what you do
to reinforce the doors.
You can install intruder alarms, but
the remote locations of many sites can
mean that there can be no timely response
to an alarm. At least the noise
generated might repel some would-be
troublemakers.
Recently, we had one of these turkeys
try and steal some live high-voltage mains
wiring. As with the suicide terrorists, if
enough of these folk started to behave
this way our problem might take care of
itself. It’s small comfort when dealing
with such a depressing topic, but I like to
think that Darwin’s theory will take a
hand and future generations won’t see so
much of this meaningless damage and
destruction.
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver. He
may be reached by e-mail at dan@broad
casttechnical.com.
62 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada DECEMBER 2008/JANUARY 2009

ENGINEERING
Bring me your lemons
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
“When you’re stuck with lemons,
you make lemonade.”
How many times have we heard that
line? This is a story of a crew of radio station
technicians that got stuck with a very
big lemon, but used it to sell a whole lot
of very profitable lemonade to broadcasters
everywhere.
In 1968, Western Broadcasting was
granted an FM licence for Vancouver. This
would be the third commercial FM in
the market, behind Q Broadcasting and
Moffat Communications. In those days,
all FMs struggled and needed an AM big
brother to support them: FM audiences
were small, and revenues even smaller.
To give you an idea of the lay of the land
at that time, Q’s CHQM-FM mostly simulcast
its AM counterpart, and Moffat’s
CKLG-FM taped and repeated much of
its programming. From the get-go, it was
decided that CFMI would use automation
to control costs.
Automation systems of the day veered
to the electro-mechanical—no hard drives
but lots of motors, tape guides and solenoids.
Music was normally supplied on
large stereo reel-to-reel transports that
could provide hours of “walk-away” time,
and commercials on (mono) cartridge
carousels, a kind of merry-go-round whirligig
that could play up to 24 cartridges in
succession. The reel machines worked
well, but caused programming limitations
because they were sequential devices. You
could mix up the order some by using a
bunch of transports, but songs still tended
to get played in a pattern that became
recognizable over time.
Here’s where that big lemon I mentioned
makes its appearance: CFMI’s management,
recognizing the limitations of
tape, decided to create what may have
been the world’s first all-cartridge allstereo
automation system, dubbed “Fat
Albert.”
Well, that was swell in theory: a programmer
would load all the music and
commercials for each play, stuffing a
bunch of carousels every few hours, and
the order everything got on the air could
be changed each airing. This made the
programming department happy. But
the cartridges of the day, “Fidelipacs,”
were just not capable of reproducing
stereo. The engineering department was
NOT happy!
There were several problems with the
Fidelipacs—wow and flutter, dropouts
and the fact that a dropped Fidelipac was
essentially a dead Fidelipac, it would (almost)
always jam the very next time it was
used. The real killer, though, was that the
phase relationship between the two audio
channels was not stable, and it turned out
to be virtually impossible to make it so.
Here’s where our intrepid CFMI engineers
came in: faced with a seemingly insoluble
problem, they ripped apart a
bunch of Fidelipacs to find out why they
didn’t work right. They discovered pretty
quickly that although some improvement
could be made by dismantling the cart
and manually “tuning the corner post”,
the best solution was to start from scratch
and make a whole new device.
The quest for a better stereo cart led
them from improvements in mechanical
design, to the picayune details of how
plastic injection moulding is done, to
the use of exotic materials such as Lexan
for the cart bodies and Teflon tape for
the pressure pads. Many hours of brainstorming
and experimenting later, they
had developed a truly superior cartridge
Boondoggle? They’ll never know!
Because you’ll know it all with the
BROADCAST DIALOGUE ELECTRONIC BRIEFING.
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which, by the way, was almost indestructible.
The engineers responsible were
Don Kalmokoff, Dave Glasstetter, Dick
Dipalma, and Doug Court, working for
Chief Engineer Jack Gordon.
And here’s where the management of
Western, in the person of Bill Hughes,
can take a bow:
Hughes had the vision to see that here
was a problem, and a solution, much bigger
than CFMI. Western took the plunge
and established a whole new division of
the company, led by Kalmokoff, to manufacture
and market their engineers’ new
creation, not just to Western stations but
to anyone that needed a stereo cartridge.
And so the Aristocart was born. Over
the next 20 years, more than a million
were manufactured and shipped everywhere.
Competitors infringed on patents,
lawsuits were launched, and there were
shortages of Lexan and lubricated magnetic
tape to contend with. But through it
all, Western made a well-earned bundle
on the side from the Aristocart division.
Today, we have different types of problems,
and don’t hear much about wow,
flutter, dropouts, high frequency rolloff,
THD or IMD, let alone phase distortion.
Instead, discussions lean more towards bit
jitter, latency, and artifacts. But it wasn’t
so long ago that four or five guys working
away at a radio station made a big
impact on our industry. Hats off to them!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver. He
may be reached by e-mail at dan@
broadcasttechnical.com.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada NOVEMBER 2008

ENGINEERING
The wonderful world of wire
BY DAN ROACH
As station technicians, we’re expected
to know all about the wire and
wiring of our physical plants. But
much information seems to be passed
down by word of mouth, and it’s sometimes
hard to find written references to
explain all the wiring bafflegab.
Case in point—do you need to use
FT4 or FT6 wiring? This rating refers to
the flammability of the wire’s insulation.
Distressingly, the plain old PVC hook-up
wire we’ve been playing with for years
carries no rating at all.
The minimum standard for wire and
cables going into a studio or transmitter
site today is FT4, which stands for “flame
test 4.” Almost any cabling you can buy
today is FT4 compliant, which basically
means that in a fire, the insulation will
not contribute to the combustion—it
may burn, but it won’t burst into flame.
In some jurisdictions, particularly B.C.
and Ontario, any wiring that runs free
through an air plenum for more than,
say, three meters, must be rated FT6. FT6
cables are usually Teflon insulated or
something similar. If your supplier refers
to “plenum-rated” cable, it’s probably FT6.
This rating means that the wire will not
release toxic gases in a fire.
FT6 wires typically cost about twice
as much as similar FT4 offerings, so it can
become important to know what you
need to use and when. Sometimes you
can’t get a particular cable type in an FT6
rating—or can’t afford it. Times like that,
you need to look at placing the wire
inside conduit or fully enclosed wire duct.
That small round beige or white telephone
drop cable, used before data came
to copper, was called Style “C.” Sometime
later, it became Style “Z.” So far as I can
tell, the wire itself didn’t change at all—
just the name. And for historical purposes,
if you’re looking at a really old installation,
you might find a two-tone green
twisted pair without a jacket; usually surface-mounted
with staples… this was
called Style “B.” Telco guys usually just
refer to any of these cables as “Style.”
Then there are the “Cats,” or Category
ratings.
UTP (unshielded twisted pair) wires
started out at Category One, which was
rated for POTS, or plain old telephone
service. You’ll never find this stuff anymore.
Cat Two is an obsolete type that
was used for IBM Token Ring networks
up to 4 Mb/s. Cat Three is still in use,
good for 16 MHz/10 Mb/s, and popular
for 10BaseT Ethernet networks. Cat Four
is an obsolete type that was used for 20
MHz/16 Mb/s Token Ring. Cat Five was
the original 100 Mb/s Ethernet cable, now
obsolete, supplanted by the very popular
Cat 5e, which is adequate for 100 MHz/
100 or 1000BaseT Ethernet. Next comes
Cat 6, rated to 250 MHz. Cat 6a is rated
to 500 MHz, which will take you up to
10GBaseT.
Cat 7 doesn’t even officially exist yet,
but informally refers to shielded twisted
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
pair cables with individual pair shielding,
and an overall shield rated to 600
MHz. It’s expected that this will carry
100GBaseT Ethernet, but right now it’s
still vapourware … don’t expect to be able
to buy it for another five years or so. And
with all that double-shielding, it sounds
like it will be a bear to use.
All these frequency ratings, when referring
to Ethernet speed ratings, are for a
maximum 100 meter run. Incidentally,
although the great majority of cabling installed
for computer and telephone
today is at least Cat 5e grade, for voice
over IP telephone, the requirement is for
only 0.8 MHz, so even Cat 3 is way more
than adequate. Whether you can find suitable
cable at your supplier in this grade
is another question, however. Sometimes
it’s just easier to not buck the trend, and
use Cat 5e or better, just like everyone
else.
By the way, the “Cat” ratings originated
with cable supplier Anixter, but the
standards today are set by EIA/TIA. These
jokers also came up with two competing
wiring schemes for RJ45 connectors,
T568A and T568B.
All you need to remember is not to
mix ’em up, and 99% of everything is
wired with scheme “B”. It’s also handy to
know that wiring one end of a cable as
“A” and the other end “B” will give you a
crossover cable!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada OCTOBER 2008

ENGINEERING
It’s giant leap of faith time again
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Lately I’ve been hearing excitement
from radio station sales managers
and some soft groans of “here we
go again” from station engineers. At the
centre of it all: the Bureau of Broadcast
Measurement’s promise of “Portable
People Meters” for radio.
As long as I’ve been involved in broadcasting
(roughly since the middle of the
Jurassic period), there’s been grumbling
about the purported accuracy, or perceived
lack of it, of BBM’s ratings which
have always relied on radio ballots. And
while everyone (perhaps excluding BBM
employees) seems to feel that these are
not as accurate as they should be, well,
there hasn’t been a proven way to get
better results.
BBM has responded to the pressure
to find a more modern method with the
promise of PPMs in the next few months.
These special radio receivers will log what
stations listeners are listening to, and for
how long. They’ll do this by decoding
inaudible identification signals encoded
in each station’s broadcast audio chain
and subsequently broadcast over each
station’s transmitter. Of course the techniques
to be used are proprietary but it
has been let out that they will involve
psychoacoustic masking. The little bit of
information that has been released
claims that the system is patented, has
been around since 1992 and works very
reliably under real-world conditions.
There’s already some experience with TV
measurements, but now AM and FM
radio will be trying this system as well.
Tricky business, this. Radio reception,
being portable, arguably is subject to
quite a bit more variable background
noise than TV viewing. And with AM
radio in particular, the bandwidth available
for this kind of telemetry is very
small. Psychoacoustic masking is wellknown
to broadcasters, and has been
one of the main tricks used to bit-reduce
audio. But the last time we heard about
anybody trying to use it this way was
when CBS Labs got embroiled in the
Copycode chip debacle, and that didn’t
work out well at all.
You might remember when Sony and
other Japanese manufacturers tried to
make R-DAT into a consumer format.
These low-cost digital audio recorders
promised to replace the popular audio
cassette format with a smaller, CD-quality
digital recording. Record industry
types, notably the RIAA in the USA, got
their knickers in a knot over the prospect
of consumers making high-quality bootleg
dubs of copyrighted CDs. CBS Labs
entered into the fray, promising to develop
a chip that could be incorporated in
the R-DAT machines that would identify
copyrighted input material by the absence
of a narrow band of audio that would be
present in all normal audio, and this
would prevent the recorder from continuing
to record. Under this system, the
critical band of audio would have to be
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcast technical.com.
notched out of all commercial CDs. The
main problem CBS encountered was that
the notching process kind of ruined the
source audio they were trying to protect.
If they moved the notch to a less critical
area in the audio band, then the system
didn’t work reliably because the audio
wasn’t always there to be filtered out.
Try as they might, CBS Labs couldn’t
come up with a satisfactory system.
Listener tests indicated that they were
mutilating the source audio. The lack of
a workable Copycode chip effectively prevented
R-DAT from ever having a chance
of becoming a consumer format in North
America. Who knows? Maybe it wouldn’t
have caught on in any event. It was about
the last time anybody heard from CBS
Labs, which was closed down shortly
afterward.
We’ve got a couple more decades
under our belts now and digital signal
processing and psychoacoustic masking
are much better understood than they
were in CBS Labs’ time. BBM may be able
to some up with a system that (a) works
and (b) is inaudible. But let’s just say that
it won’t be easy, and wait on developments.
If these encoders do produce audible
degradation, broadcasters will face a
difficult choice: whether to accept them
anyway, for the sake of more accurate
audience measurements, or to demand
something truly inaudible, which may be
impossible to achieve in practice, in order
to keep more audience in the first place.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada SEPTEMBER 2008

ENGINEERING
Pre-processing audio for digital
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
It’s been a very poorly-kept secret that,
from the dawn of digital processing
and continuing to the present day, digital
processors and stereo generators have
generally been able to benefit from having
an analog gain-controller placed just
upstream, in front of them. Now, with increasing
interest in optimized audio for
streaming applications, the need is being
felt even more.
The first-generation digital boxes were
notoriously finicky to set up in the first
place. Anything you could do to narrow
the variations in the quality of material
that the digital processor saw would reduce
the amount of fiddling around with
what were then little-understood controls
once the audio was in the digital domain.
In a way, it’s surprising, but this is still true,
even with the newer generations of digital
whiz-bangs—uniformity of product on
the input yields better sound with fewer
artefacts on the output.
This must be partly due to the variations
in the quality of the source material
that we provide. We should always keep
in mind that our processor gurus are optimizing
their algorithms and designing
primarily for a form of audio that is becoming
a rarer and rarer bird, indeed—
“unprocessed” or “raw” audio.
Even if we take pains to use a storage
system that is uncompressed, and perhaps
even an STL system that doesn’t use bitreduction
techniques, we still need to be
concerned about our audio sources—as
commercials are swapped back and forth
between radio stations and studios, MP3
files are being created and re-expanded,
sometimes with more care than others.
The music distribution services seem to
be taking some care but, here again, consumer-oriented
AAC and MP3 files of
“difficult-to-get” music seem to have a way
of seeping into systems, past even the
most vigilant and discerning audio
policemen. And increasingly, and even
more disturbingly, music is being mastered
by the record companies with
built-in crunching, compressing, and
even clipping.
Well, these are variations that we
might just have to accept. As the world
continues to change, maybe we’ll eventually
drift into an alternate universe where
we will once again have control over these
things, but in that respect it will not resemble
the one we’re in right now. So
we’re going to have to make the best of
the situation in which we find ourselves,
and fix what we can.
Whether the audio that’s going to be
processed ends up in a non-bit-reduced
form such as an FM composite signal,
or gets crunched down mercilessly to a
low-bit-rate creature such as an Internet
stream, what can we do to get the most
out of our nth-generation digital bitflinger?
Consistent input levels and equalization
are desirable, but not if they come
along with “analog” artefacts such as
Sept 18–21, 2008
at Horseshoe Resort just
north of Barrie.
Contact Joanne Firminger
for details at
1-800-481-4649.
www.ccbe.ca
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
pumping and breathing noises… and,
we’re told by all the designers of bitreducing
algorithms, absolutely with no
added clipping. We need something gentle
and slow—a gated, automated gainrider
like the Audimaxs and Texars of
yesteryear. Preferably with several audio
bands, not so much for equalizing, and
definitely not for pre-emphasis, but only
to help keep the “tonal balance” more
similar between different audio sources.
The guys that developed the CBS
Dynamic Presence Equalizer, a fairly terrible
box from oh-so-many years ago,
might have been on to something after
all. Or maybe just the beginning of
something.
Come to think about it, something
like this (in the digital domain) might
be just what’s needed to rein in the
audio level problems being experienced
by HDTV stations, for completely different
reasons (only they’ll need it for 5.1
audio!).
We live at the dawn of this digital age,
and it’s comforting to think that in a few
years our level control and quality control
problems will all have been solved.
In retrospect, some of our approaches to
today’s problems will no doubt seem
quaint. At the same time, it seems ironic
that the key to ironing out some of these
troubles may lie in the audio processing
techniques of the past.
78 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada JULY/AUGUST 2008

ENGINEERING
I, Bach returns!
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Just back from the National Association
of Broadcasters convention, our annual
bacchanalia of technological excess,
and full of notions of broadcasting’s past,
present and future.
Those that were expecting the annual
showdown between Avid and Apple were
disappointed, as neither made an appearance
at the show. With the no-show of two
of the biggest exhibitors, the flavour of
the exhibition has changed perceptibly.
Other changes: TV types from the
Central Hall continued their incursion
into the North Hall, formerly virgin radio
country. This has reinvigorated the Radio
Hall, which had been shrinking gradually
year by year and was becoming decidedly
prune-like. And this was the first
year that I noticed the South Hall (upper
and lower) has definitely become the
busiest area of all. The whole centre of
SRW-5800
The SRW-5800 is capable of recording at an
amazingly high video bit rate of 880 Mb/s.
The recorder is equipped with the same key
features as the SRW-5500 and SRW-5000
recorders in the series, but exclusively provides
the outstanding capability of 1080/60P and 50P
recording through the use of 880 Mb/s data rate.
The 1080/60P and 50P recording system is
equally ideal for origination of progressive-based
programs, 720P programs, and high-quality
slow-motion programs.The 5800 also boasts the
capability of supporting file based workflow with
the optional Network/File card.The SRW-5800
can also record or play out Cineon or DPX files
across a GigE Network while simultaneously
providing HD conversion.
With the support of an extensive range of
signal formats, including 1080/60P and 50P, plus
outstanding system versatility and reliability, the
SRW-5800 HDCAM-SR Studio Recorder should
be the universal choice for high-end content
creation today and in the future.
gravity of the show seems to have shifted
to new media and away from the traditional
feeding frenzy in Central Hall.
Do you remember when the main object
of IBOC radio was to provide a highquality
replacement signal for analog? In
these days of shifting priorities, someone
needs to remind iBiquity and their minions,
because the goalposts keep on sliding
around.
Now that they’ve got fairly decent
audio quality (at least on the test bench),
suddenly the essential goal is to have as
many channels as you can. To that end
they’ve introduced an extended version
of FM IBOC that gives you more bits at
the expense of increased interference to
the analog signal. And there’s a move to
increase the relative level of the digital
signal ten-fold or so, as apparently it has
been discovered that -20 dBc (decibels relative
to carrier) isn’t effective at penetrating
office buildings and the like.
If you ever thought that Canada’s traditional
position, well behind the U.S.
bleeding-edge of technology, was wise, it’s
time to hold that thought. If this proposal
is approved, any of the early-adopters
down south that had chosen a hybrid
approach to IBOC will be tearing everything
apart and starting over. Headroom
is one thing, but 10 dB = a new digital
delivery system.
In my more cynical moments, I’ve
concluded that these guys are just going
to keep screwing around until they completely
wreck the spectrum. They just
don’t seem content to settle for the level
of chaos they have achieved to date.
And I’m getting really, really tired of
so-called technical people saying that 36
kbits or 24 kbits/sec “equals” or is “the
same as” (a) CD quality, (b) FM quality,
or (c) insert your favourite standard here.
It isn’t—usually it isn’t even close.
Please don’t insult my intelligence or my
ears. It may be the best that we can do,
but don’t try to B.S. us all with words like
“equals”. Makes the whole thing smack
of snake oil.
On a more positive note, the IBOC
team has come up with a really killer application
that caught my eye. It’s almost
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcast
technical.com.
enough to give you faith in the technology.
A couple of new receivers have been
introduced, originally exclusive to Apple
stores in the States. These little table
radios have iPod sockets, as is the current
fashion for such devices. They also have
a little lighted pushbutton called “Tag”.
Here’s the drill: you’re listening to your
favourite IBOC FM station when you
hear a song you like. If the “Tag” button
is lit up, you can press it, and the radio
will automatically store PAD (Program
Associated Data), containing the song
title and artist and the radio station’s ID,
into memory. When you plug in an iPod,
the data goes there. When the iPod is
subsequently plugged in to a computer
with iTunes, iTunes conveniently searches
for the music and lists it for downloading.
If you download it, Apple sends
a small commission back to the station
that provided the Tag data.
All this was predicted 15 years ago
with DAB’s “coupon radio”, but it’s just
so much more effective to see the stuff
actually working. The radios and the service
are available right now. Apple covers
all the front-end costs and provides the
PAD to the radio station. And they are
apparently prepared to pay the stations a
small fee for the service.
It all seems to work rather seamlessly,
but I hope you’ll excuse just a little
scepticism, if only because I saw it at NAB,
the original home of smoke and mirrors.
In the words of the all-powerful, allknowing
Oz, “Ignore the man behind
the curtain…”
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada JUNE 2008

ENGINEERING
Extra! Extra!
More broadcast features for you!
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Lately, there’s been a lot of discussion
about the huge expense of converting
all our over-the-air television
stations from NTSC to ATSC, and who’s
going to pay for it, and how.
Sorry, I don’t know, either.
But for the last little while I’ve been
ruminating about all those little extra
add-ons that television broadcasters are
already expected to provide. I guess they
fall into two categories—those that are
useful (to someone) and those that really
are just a waste of time.
What they all seem to have in common
is added expense for the broadcaster,
and no visible means of support. I’m
not talking about colour TV and BTSC
stereo, which were certainly added costs,
but were for the benefit of all viewers,
and not just a minority.
The first one to come along was probably
closed captioning for the hearing
impaired: a nice little enhancement that
could be added to programs in the vertical
interval, and before you know it, it
became all but mandatory for all programs.
Woe betide the broadcaster that
has some sort of technical problem and
doesn’t get those captions to air! If you
have ever wondered if anyone’s paying
attention to these details, try omitting
them and watch the switchboard light
up. The captioning police are out there.
Then, of course, we have so-called
descriptive video, which isn’t video at all
but a verbal description on the SAP channel
of what’s happening on the screen,
for the vision-impaired. In the blink of an
eye (sorry, no pun intended), that seemed
to become mandatory, too, and you’d
better have a jolly good reason for screwing
up that feed.
Of course, thanks to Professor Tim
Collings at our own Simon Fraser
University, aided and abetted by the usual
suspects, we now have mandatory program
classifications, both open and
closed, with the V-chip and the AGVOT
(Action Group on Violence on Television)
standards. Not only are the French- and
English-Canadian standards different
from each other, but they aren’t directly
compatible with U.S. standards either, so
imported programs need to have the original
classification (mostly) overwritten
and the Canadian standard punched-in
over top.
Now each of these, taken alone, is
probably not going to break the bank.
But it’s starting to look like the death of
a thousand cuts. And while these are all
laudable efforts, the responsibility and
But over and above all that, there is probably not a
broadcaster in all of North America (or the world?)
who is configuring metadata for each program segment
in the way that Dolby hopes and expects them to do.
cost of providing them always seems to
land on the broadcast operator.
Well at least the foregoing are (hopefully)
useful for someone. We’re not so
sure about the following.
With the advent of HD television, we
have a couple of new ones.
First, the lords of Dolby, who somehow
seem to have become the selfappointed
standard bearers of the audio
portion of HDTV, have decreed that television
stations should send metadata to
help “intelligent” HDTV receivers with
setting their audio level controls. First of
all, this whole metadata concept, as we
have discussed in this column in previous
issues, is in the writer’s view hopelessly
optimistic and doomed to failure
in the real world.
But over and above all that, there is
probably not a broadcaster in all of
North America (or the world?) who is
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver. He
may be reached by e-mail at dan@broadcast
technical.com.
configuring metadata for each program
segment in the way that Dolby hopes and
expects them to do. The metadata is virtually
always set to some arbitrary level
by the broadcaster, and left there forever.
Not what Dolby had in mind.
Quick, now: hands up if you are resetting
your metadata bits differently for each
program segment! (I didn’t think so.)
And now it comes out that HDTV has
its own new closed-captioning standards,
over and above the SD captioning.
According to a digital broadcast standards
expert at a recent seminar put on
here in Vancouver by Applied Electronics
and Tektronix (and by the way, a big
thank you to Applied and Tektronix!), the
HD captioning standard has probably
NEVER actually been used by ANYONE
in the real world. It’s complicated, and
it’s cumbersome, and whoever is doing
the captioning is already required to provide
the old SD closed captions anyhow.
There’s just no reason to do the whole
thing over again to the HD standard.
So, somewhere, someone is probably
working on a rule to require it.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MAY 2008

ENGINEERING
Audio monitoring in the control room
BY DAN ROACH
Ahh, monitoring. Much has been
written, but broadcast practice
seems to differ in some respects
from what the textbooks have to say. Of
all the different areas of a radio station’s
technical plant, the monitoring system
must be among the most controversial,
the least backed-up by science and the
most able to keep operating staff comfortable
during the day, or not.
Loudspeakers come in a bewildering
array of sizes and shapes. For our purposes,
let’s stick to two-channel stereo (and
save surround for another day), and fairly
“normal” low-impedance electromagnetic
speakers. There are certain words
that we could classify as jargon that usually,
but not always, have a certain meaning.
“Bookshelf speaker” is an example.
This usually means a speaker that is intended
to be placed inside a bookshelf
cabinet for proper bass response, and may
be a bit weak on the bottom end if it’s
placed out in the open. But sometimes it
just refers to a speaker’s case style.
Buyer beware!
Watch out for speakers with bass relief
ports in the back—they should have
at least 25cm clear space behind them,
so make sure that you don’t back them
up against anything. A surprising volume
of air can pump in and out of those ports
(drive one and put your hand back there
to see for yourself), so make sure they can
breathe.
Speaker placement is often determined
near the end of control room construction.
There are many ways to mount a
speaker but I personally prefer hanging’em
from the ceiling. This provides
lots of options for location and also,
when done properly, it cuts down on inadvertent
transmission to cabinets, walls,
and other surfaces.
Traditionally speakers are mounted in
front of the operator at approximately
head height and forming a horizontal
equilateral triangle with the operator’s
head. If there’s a chance anyone’s going
to walk into them, I pull’em high enough
that folks won’t get brained. You’ll get
better results if you have a minimum of
objects between the speakers and the
operator. The less you have to deal with
reflections and inadvertent transmission
media, the happier you will be.
One of the funnier episodes I’ve been
through with monitor speakers was many
years ago with a monitor we’ll call Brand
X. These were originally very modest closefield
monitors (priced at a little over $100
per speaker) for the consumer market, certainly
not intended for professional use.
But word got out that super-producer
Quincy Jones had used these particular
monitors for his mixdown of Michael
Jackson’s Thriller record album.
Lemming-like recording studio mixmasters
just had to have these wonderful
speakers for themselves. The only problem
was that they just weren’t very wellsuited
for high-end use. No worries: There
Dan Roach works
at S.W. Davis
Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcasttechnical.com.
were numerous further articles in the industry
press, detailing secret modifications
that would improve performance.
First of these was to remove the speaker
grilles. Unfortunately, this gave the speakers
an overly bright sound. The next brilliant
idea was to tape a piece of toilet
tissue over the ribbon tweeter to attenuate
it a bit. The main problem with that
was that it caused standing waves to be
set up inside between the tweeter diaphragm
and the toilet tissue, producing
a comb filter, or flanging effect. Next
came printed comments on the relative
merits of various brands of toilet tissue,
with the burning issue being whether to
go with two- or three-ply.
I’m not kidding.
This presented Brand X with a unique
problem. While they sold a ton of these
speakers to the gullible, they risked being
laughed out of the business by the few
folks actually listening to the results. In
fairly short order, they came up with a
“Pro” version, still carrying the same
model number (at a much higher price
point). The new version actually bore no
resemblance to the original. It came without
a cloth speaker grille, since by now it
was known that the studio guys would
just remove it anyway. Instead, it had an
expanded metal grille, which some wag
suggested was to stop exploding speaker
cone parts from impaling hapless operators.
It was a far more suitable speaker and
went on to be used in many studios. And
the studio operators were happy, thinking
(incorrectly) that they had something
in common with the great Quincy Jones.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada APRIL 2008

ENGINEERING
Acoustics and monitoring, Part Two
BY DAN ROACH
Last time we discussed soundproofing.
But often when folks complain
about sound in a room, they are
referring to excessive sound wave reflections
taking place inside a room.
Small rooms tend to have certain
common acoustical problems. One can be
excessive reverberation time… too many
reflections off too many hard surfaces.
When we’re building studios, we can
try and avoid parallel walls and square
rooms. Doing this will help reduce the
habit of reflections forming standing
waves. But if the room is already built,
what can we do to repair bad sound?
Of course we can treat walls and ceilings
to be more sound absorptive. The
trick here is to try and absorb the lower
frequencies, and the higher tones will take
care of themselves. High frequency reflections
are very easy to attenuate, but if we
don’t treat the lows as well we end up with
a very “boomy” room. The main thing to
remember is that for good low-frequency
absorption, the medium must be quite
thick.
The all time champion sound absorber
is friction-fit fibreglass. The loose
fibres form labyrinths in which sound
waves get lost. Great things have been
done with fibreglass batts mounted on
walls between studs, covered over with a
loose weave material. Unfortunately, fibreglass
fragments will eventually migrate
through the material and get into the air,
where they are very unpleasant. One
alternative is to place an airtight layer of
polyethylene sheet between the fibreglass
and the covering material… the plastic
sheet does reduce the efficacy of the fibreglass,
but by less than you might expect.
Whether or not you use a plastic sheet,
nowadays you need to make sure the
cloth covering material is fireproof.
There are commercial products available
using stiff fibreglass board covered
with colourful fireproof cloth. These can
work almost as well as the loose batts,
but are most effective if mounted off the
wall by an inch or so, which increases
their effective thickness.
Acoustic foam is easy to use, but again
thicker is better. Avoid the temptation to
purchase thinner stuff (you get twice as
much coverage per dollar, but the low frequency
absorption is not nearly so good).
One of the things that you may discover
quickly, is that you’re not after absolute
absorption. Some reverberation is
expected and desirable. You can tell right
away when you’re in a room with excessive
treatment. If it’s the wrong kind, and
the low frequencies are unattenuated, the
room sounds boomy and hollow. If
there’s too much absorption of all frequencies,
the effect is a dull and lifelesssounding
room. It’s far better to add
treatment gradually, a piece at a time,
until you reach the desired effect.
Much experimenting has been done
to produce a small room that provides
good stereo imaging and is non-fatiguing
Dan Roach works
at S.W. Davis
Broadcast Technical
Services Ltd., a
contract engineering
firm based in
Vancouver. He may
be reached by e-
mail at dan@broad
casttechnical.com.
for the listener. While there are all sorts
of approaches, here are some generallyaccepted
guidelines:
1) For optimum stereo, speakers are often
set up at the front, positioned to form
an approximate equilateral triangle
with the listener. Typically the speakers
are oriented “tweeters out” for
maximum treble dispersion, although
in more than 20 years of looking I
haven’t been able to find a printed
reference that calls for this practice.
2) It’s important that the operator have
a good casual line-of-sight in order to
see staff comings and goings. The monitors
prevent hearing the approach of
staff members, so visual cues are essential
to prevent inadvertent heartstopping
surprises. I’ve seen truck style
rear-view mirrors installed on speakers,
and have worked in enough control
rooms to know why they’re there.
Line-of-sight to other working studios
and control rooms, while not essential,
is always appreciated.
3) An interesting room variation is the
so-called “live end/dead end” (LEDE)
studio. While there’s a whole set of
rigorous specs to LEDE, the basic idea
is to make the front of the room (forward
of the operator’s ears) absorptive,
and the back of the room reflective.
In theory, at least, this can provide the
listener with exceptional aural cues, results
in excellent stereo imaging and
a low-fatigue environment.
4) If you’re in a situation where you want
sound levels kept lower, place the
speakers close to the operator. Closefield
monitors can be used to good
effect for this kind of environment.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MARCH 2008

ENGINEERING
Acoustics and monitoring
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
...which in radio nowadays, means
the acoustics of small rooms.
Two basic, separate concepts that people
often will intermingle are soundproofing
and reverberation.
By soundproofing we mean unwanted
sound getting into and out of our sound
rooms. Often, when folks are complaining
about soundproofing they really are
remarking on excessive reverberation in
a small room, which is caused by sound
waves reflecting off walls and surfaces inside
the room itself—and is a problem
separate from soundproofing.
Soundproofing is one of those topics
that starts out pretty simple and then gets
progressively more complex, and really
never ends. We are really fairly lucky in
broadcasting in that we just need to keep
extraneous sound under some sort of
control; we don’t need to stamp it out
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completely. Aesthetics and convenience
are more important to us than absolute
acoustic isolation.
First off, a soundproof room must be
airtight. (We’ll get around to ventilation
in a minute, please hold your breath until
then). That generally means you can forget
about using the space above the drop
ceiling for a return air plenum. Walls must
go all the way up and seal airtight, or our
cause is lost before we start.
An alternative is to build a “boxwithin-a-box,”
with a lowered solid ceiling
that is sealed at the tops of the walls.
The next step is to reduce transmission
through the walls. There is really no
substitute for friction-fit fibreglass insulation.
It is just the best thing there is for
sound absorption. The loose fibreglass
fibres trap sound waves and absorb them
like nothing else.
Proper sound doors are big, heavy and
expensive. The good ones are filled with
lead, but often enough a good steel door
filled with corrugated cardboard or some
such will suffice for broadcast radio.
Do take the extra weight of a sound
door into account, and call for heavyduty
hinges, and lots of them, and extra
heavy duty door closers and door frames.
Automatic dropping thresholds on doors
are frequent trouble spots later, but they
are really hard to avoid at this point.
Now we’ve covered the basics; from
here it’s a matter of degree. Just how good
do we need our sound partitions to be?
Starting with single wall, we can add additional
wallboard on one side or both
(preferably glued so that nails won’t transmit
through the inside wallboard layers),
go to double stud, stagger stud, double
wall or even double wall with a resilient
dead space in the middle. And you can
seal the walls with airtight lead sheathing
inside if you’re still not satisfied.
As we continue to move up the studio
soundproofing food chain, we pass
through simple flooring to floors with
insulation and resilient sleepers, floating
concrete floors and floors sealed with lead
sheathing. Somewhere along the way, we
upgraded to double doors and sound
vaults at the sound room entrance.
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd.,
a contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broad
casttechnical.
com.
Windows need a little special attention.
Single panes, even of double- or
triple-glazed glass, will allow sound to
transmit through a partition. Double
panes are much better, preferably of
double-glazed glass or better. But they
must be mounted in a way so that they
are not parallel to one another, or vibrations
on one side will transmit to the
other. They should be mounted with
something resilient between the glass and
the centre reveal, and preferably the reveal
split with a resilient channel to reduce
communication between the two sides.
The glass and frame must be airtight
on both sides of the partition. A small
hole inside the frame into the surrounding
wall is permissible, and will help prevent
compression waves from allowing
vibrating glass on one side setting up
sympathetic vibrations on the other side.
Further enhancements would include
thicker glass panes or a third, centre pane
to further reduce transmission.
We’re eventually going to need fresh
air, and since we got rid of the return air
plenum up near the top of this page, we
have to do something about exhaust air
as well. Both the fresh and return air
ducts need to be run through labyrinths
to prevent sound transmission to and
from adjacent rooms. After all the effort
we’ve gone through, it would be crazy to
allow sound to transmit easily through
the ducts.
Next time, some thoughts about reverberation
and monitoring in small spaces.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada FEBRUARY 2008

ENGINEERING
Strange radio stories of yore
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
Circle round the campfire, while
Grampa Dan tells you some weird
tales about radio engineering in
the grand old days!
Perhaps you’ve already heard the yarn
about radio stations where the engineering
department blacklisted the playing of
Crystal Gayle tunes. It seems the young
lady’s singing voice could, and did, hit
certain combinations of notes that would
cause the grids in Eimac’s 4CX15,000A’s
to vibrate sympathetically. The result was
that every time the station played a Crystal
Gayle song, the tubes’ internals would
vibrate and short out and the transmitter
would overload and shut down.
You can imagine the skeptical response
that this story first received. After
they got up from the floor laughing, however,
Continental engineers (whose transmitters
were tripping) did a little field
work and confirmed that this was indeed
what was happening.
Early FM exciters were not the most
stable of beasts, and some of the early
modulated oscillators didn’t take too well
to the heavy bass drum tracks supplied
by rock and roll bands, especially if they
were combined with an aggressive processor.
The result was usually loss of frequency
lock, and a moment or two off
the air. Better exciters, with two-stage
phase locked loop circuits, were rapidly
deployed.
In the mid-1970s, a lot of attention
went into various tricks to give the station’s
sound a competitive edge. Especially
at Top 40 stations, the programming department
might “fiddle” with hit songs to
“improve” them, by messing with equalization
and compression before carting
their masterpiece for use on-air.
Many programmers would also edit
bits and pieces out of songs to create a
suitable broadcast version. One of the
favourite tricks was to speed up the turntable
for the dub just a bit, on the theory
that once listeners heard the sped-up
version, the original, slower edition of
the song (hopefully still being
played on the competing
radio station)
would sound dull
and lifeless.
Of course,
given the simple
techniques
in use, speeding
up the record also
increased the
pitch... and operating
on the proven
programming premise
that if a little is good, then
a lot is better, what started as a very slight
adjustment rapidly escalated into something
much worse. I can remember Beatles
tunes where the Fab Four sounded like
they were singing falsetto. Digital pitch
conversion, that would have allowed
separate control of pitch and speed, was
not yet on the broadcaster’s horizon.
Another trick that started out simply,
then became more elaborate over time,
was the use of reverberation. Simple to
perform with many digital processors
today, back then the preferred approach
involved transducers, springs and
microphones. The theory was that the
resultant sound was fuller, and louder,
and perhaps made a transistor radio with
a three-inch speaker sound a little better
than it would have with untreated audio.
The spring method worked, but there
were a few shortcomings: the reverb unit
was microphonic (i.e. it would be best to
keep fairly quiet when you were around
it, as your voice could easily set the spring
to vibrating, and you might inadvertently
end up on the air!), the sound could be
metallic, and there were certain frequencies
that needed to be avoided or the
spring would start to resonate and, given
sufficient provocation, really take off.
All I can tell you is that the Paul
McCartney tune Mull of Kintyre featured
an extended bagpipe solo, and every time
I heard it on our station I heard what
sounded like a bunch of cats harmonizing
on the chorus. Mercifully, the song
was only a minor
hit, or I would
have been forced
to institute a “no
bagpipes” rule at
the station—and
you can imagine
the standoff that
would have caused
with programming!
Of course, once programmers
started messing
with the razor blade one
thing led to another, and it culminated
in broadcast duets that
never really happened, such as Barbra
Streisand’s performance of You Don’t
Bring Me Flowers with Neil Diamond.
This sort of thing proved so popular that
record companies started producing
authorized “synthetic duets”, and that
can be followed in a straight line to
today’s sampled, looped and dubbed
hip-hop material.
Oddly enough, nowadays much better
tools for manipulating tunes are available,
yet the practice (in radio stations at least)
seems to have mostly disappeared. And
perhaps we are all the better for that!
62 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada DECEMBER 2007/JANUARY 2008

ENGINEERING
It’s AES/EBU for you!
BY DAN ROACH
The advent of digital audio transmission
standards began for me
with Denon CD cartridge players.
These were the first devices to cross my
path that had an XLR connector for digital
output. And so began the transition to
digital audio standards. And there have
been a few surprises along the way.
The first thing to know about digital
audio wiring is that the various common
formats available—whether they use balanced
shielded wire, or coaxial cable, or
fibre-optic cable—are all very similar, and
it’s usually quite easy to adapt from one
to another.
The second thing to know is that
99% of all problems are related to impedance
mismatches. The high bit-rates
involved make digital audio look and act
more like RF than audio and, as a result,
if you think of the signal as an RF carrier,
you’ll intuitively stay out of much
trouble.
Okay, first the good news—in true
digital fashion, this digital audio signal
will not pick up hum, or impair its frequency
response, or get audibly distorted
by travelling around the radio station.
The bad news is that the inevitable degradations
are largely undetectable until they
reach the equally inevitable digital cliff,
at which time operation becomes flaky
and unreliable.
And nobody wants that!
The main differences between “digital
twisted pair” and the regular analog product
are found in the characteristic impedance
of the wire, and the capacitance
of tip and ring to ground (are we allowed
to still call the conductors tip and ring?).
Our normal shielded twisted pair 22 AWG
wire has a typical, but generally unspecified,
impedance of 40 to 80 ohms. The
AES/EBU specification for digital cable
allows for 88 to 132 ohms, with the ideal
impedance being 110 ohms.
While you can generally get away with
using old familiar wiring for short jumpers,
if your signal is going farther than, say,
15 metres or so, you’re going to need to
use digital wiring.
As a consequence of the higher impedance
and desired lower capacitance,
you’ll find that the wires tend to be smaller
(26-24 AWG) and hence more fragile.
And the insulation, being foam-based, is
thicker, softer and tougher to strip off.
Take care not to crush the wire, as that
insulation will compress easily, and the
conductor spacing is a critical factor in
maintaining the specified impedance.
The AES/EBU standard calls for the
use of shielded cable, but the common
mode noise spec is so loose that, really,
the shielding is not needed. All of which
is moot, because when you’re shopping
for digital wire, shielded is what you’re
going to find. And it will be expensive.
Since you’re paying for shielding anyway,
you should look for a cable that has braid
shielding. Foil alone is most effective at
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
shielding below 1 MHz, and our digital
signals are going way above that!
One thing to bear in mind is that,
even though you’re spending the big
bucks on that special wire, your transmission
lengths are still limited to 300m
or so. The exact distance depends upon
your bit-rate. Your signal can travel much
farther at 75 ohms using coaxial cables,
but you’ll need balun transformers to
impedance-match and unbalance the signal
unless your equipment already has unbalanced
I/O. Since TV stations are generally
running all sorts of precision 75
ohm cable around anyway for video, this
option is quite popular in TV-land.
Although special “digital audio coax”
is available—and of course recommended
—it’s difficult to find much wrong with
using a precision “analog video coax” for
digital audio.
Digital video transmission, with its
bandwidth requirement up into the multi-GHz,
is of course another story. But it’s
always okay to use a “digital” cable to carry
analog signals.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada NOVEMBER 2007

ENGINEERING
Just looking for trouble, Part 3
BY DAN ROACH
As promised, some final thoughts on
the subject of preparing for (and
coping with) emergency situations.
There is very likely a local committee
on disaster preparedness that covers your
area. Make it a point to connect with them,
at least temporarily. They may have the
power to give you free access to resources
that a broadcaster can only dream about.
Even if you don’t end up with direct access
to their resources, at the very least
you (and your newsroom) will have 24-
hour contact information for the key folks
that will be at the centre of any sort of
emergency.
It is important that local government
representatives know what role your station
can reasonably play as a local disaster
unfolds… both your strengths and
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new SR8000 series
LPFM transmitters
from 100 to 2500 watts
• A very compact 19" rack format, up to 8
RU height.
• SFN capability
• Digital exciter
• Transmitter remote control and monitoring
via SMNP and web interface
• State-of-the-art MOSFET technology in
power amplifier
• Easy startup and maintenance.
Visit us at
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Rohde & Schwarz Canada Inc.
750 Palladium Drive, Suite 102
Ottawa, ON K2V 1C7
Phone: (613) 592-8000
Fax: (613) 592-8009
Toll Free: (877) 438-2880
www.rohde-schwarz.com
weaknesses. From personal experience, I
can say that these committees often have
outdated and unrealistic ideas about the
capabilities of today’s broadcasters.
First and foremost, they need to know
how to contact key station personnel at
the onset of an event. In our highly automated
age, this is no longer as simple as
it once was. Local officials are quite likely
unaware that your facility may not be
manned overnight and on weekends!
Committee members may be counting
on you to disseminate vital information
in a crisis, and can often help strengthen
your response by helping you with their
own resources. For instance, in a wintertime
case in northern B.C., a sudden transmission
line failure forced BC Hydro into
a position of forcing rotating blackouts
throughout the region. Hydro was able to
see that the local radio station, which had
no backup power of its own, was kept
powered up at the studio and transmitter
sites so that local residents could be informed
of what they could expect from
the power company over the next few
hours and days.
In this case Hydro and local radio,
working together, were able to greatly reduce
the danger and anxiety in a critical
situation (unless you’ve experienced an
extended power outage in a northern winter,
with ambient temperatures of -30 C
and lower, you’ll have to use your imagination!).
Neither party working alone
could have been as effective.
Remember my comments on CFAX
and Victoria’s disaster response during
their “perfect storm?” One of the problems
municipal staff had, even though in
this case CFAX was staffed throughout the
event, was getting through to the radio station
to pass on timely information. The
station’s switchboard was quickly swamped
by listeners.
This is another example of something
that could have been very easily avoided
with an ounce of foresight. The emergency
folks assumed that CFAX would be onair,
and that they could get through easily.
At least they were half right!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
Finally, a couple of random thoughts
about preparation.
Earlier we discussed the notion of
broadcasting from the transmitter site.
Further to that, it might be a good idea
to prepare a little package of non-perishables
at the site, and seal it up so that
critical pieces won’t wander off while we
await Armageddon. I’m particularly fond
of those flashlights and radios with the
cranks on them instead of batteries inside,
but you’re free to stock up on whatever
you think might be most useful.
Don’t count on using cell phones in
any emergency; they are inevitably the first
to go!
And finally, the last big earthquake in
the San Francisco area showed an alarming
number of broadcasters were disabled
when electrical power failed. Although
most of them had diesel generators,
most of the fuel tanks fell over when the
ground shook, becoming useless exactly
when they were most needed. For goodness
sake, if you live in an area prone to
earthquakes, fasten those tanks to your
building wherever practical.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada OCTOBER 2007

ENGINEERING
Bulletproofing your site, Part 2
BY DAN ROACH
While there can be no substitute
for “fundage” when it comes to
securing your sites against disasters,
there are all kinds of preparations
you can make that will help when disaster
strikes. And some of these don’t have
to cost very much to implement.
For now, let’s concentrate on the first
part of the problem we identified last
time—staying on the air during a natural
disaster.
Most off-air time involves hydro outages
or telco line failures, so the obvious
places to reinforce your operation are with
standby transmitters, standby generators,
and STL systems that allow you to bypass
telco problems. These can all be high-cost
items, but sometimes there’s an alternative
that is not cost-prohibitive.
If you can’t afford automatic backup
power at the studios, perhaps a manual
backup power system is practical. I have
seen viable studio backup power systems
consisting of a 3-kW pull-start generator
in a box in the station parking lot, with a
manual transfer switch to connect power
to the racks and control rooms as needed.
It’s important that everyone understand
that this is a stop-gap solution. It
obviously is not effective against a shortterm
power outage, as it will take time for
someone to find the key and work the
controls. But it could be very handy in
an extended outage.
One thing we have all learned is that
it is unrealistic to expect utilities to show
up and help you anytime soon when there
is a crisis. They will have their own problems.
It’s also not realistic to try shopping
for a generator once the lights go out.
You need to plan for this kind of thing in
advance.
If you’re using an RPU system for remotes,
maybe it’s practical to install a
couple of extra antennas at studio and
transmitter sites, so it could be quickly repurposed
as an emergency STL.
If studio back-up power just isn’t going
to happen, how about back-up audio?
One nice thing about telco program lines
is that the phone company supplies reliable
standby power for them as a matter
or course. A properly-programmed iPod
with a repeat transformer to patch into
the program line, either at the studio or
the transmitter site, is a viable source of
backup audio, whether or not there is studio
power, and it can keep you on the air.
Cost? Less than $200 complete.
Add a mic mixer, or even a minidisk
recorder, a couple of microphones, headphones
and radio receivers, and you have
a kit that will allow you to broadcast live
from either a powerless studio or a powered
transmitter site. And you’ve still spent
less than $500, even less if you have any
old gear available (who needs mic mixers
at remotes anymore?).
Maybe you want to add some flashlights
and other essentials, and put it all
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
in a sealed box, secure and complete until
it’s needed. Or maybe an iPod and a program
switcher at the transmitter site are
all that you require.
We would all like back-up transmitter
sites, but here again they may appear costprohibitive
at first glance. But in smaller
or medium markets, an FM exciter and an
antenna on a stub of a tower at the studio
can be a viable alternative. This may cost
you less than $15K to implement, even
from scratch. That’s pretty cheap insurance.
Again, if you just can’t afford back-up
studio power, have a look at your telephone
system. Your PABX has an unpowered
fallback position that will allow
direct connection of the trunk lines to
old-fashioned unpowered telephones. You
just need to make sure that the phones
in question are in the areas you want
them, so your newsroom can take and
make calls during an outage. Cost? $0.
Some stations are blessed with management
that values reliability of service,
and there is no substitute for proper
backup systems already in place. With
adequate redundancy, your station can
confidently weather the storms, even
when things get nasty. But even with a
limited budget, there are some small measures
you can take ahead of time that will
help you stay on the air if disaster strikes
your plant.
Next time, some final thoughts and
tips on preparing for the unexpected.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada SEPTEMBER 2007

ENGINEERING
Thinking the unthinkable:
Disaster-proofing your plant
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
An area-wide natural disaster, large
or small, can be a chance for radio
either to show its best capabilities
to the community, or suffer a terrible loss
of reputation if it fails to measure up.
Today’s increased automation, with
attendant scaled-back staffing, makes it
more challenging to respond in a timely
manner. Advance planning is more important
than ever. This can’t be stressed
enough—by the time disaster strikes, your
options have already become extremely
limited.
Here, really, is a case where an ounce
of preparation can make all the difference.
Two parts to this problem—how to
stay on the air in a disaster, and how to
be in a position to transfer vital information
over your station. Skilful delivery
of the second part offers the reward, but
there can be no second part without the
first, and that’s mostly where the engineering
department can help.
Some examples of heroic past efforts
—since I’m on the west coast, these come
from this end of the country, but you can
no doubt supplement them with some
closer to your home: Broadcast Dialogue
featured extensive coverage of the ice
storms in Central Canada and flooding
in Manitoba, not so very long ago.
October 1963: Hurricane Freda strikes
Vancouver, late in the evening, a lot
harder than predicted. One by one local
radio stations drop off the air as transmitter
power fails, so that when morning
arrives, and people start waking to the
mess that Vancouver has become, there
is only one station on the air—CKNW.
’NW is down to 1 kW and its third transmitter,
and is running on a small gasoline
generator and Coleman lanterns at
the studio, but it is still on the air—and it
takes out ads in the newspaper afterwards
to remind everyone who it was that was
still standing when disaster struck.
July 1994: A forest fire near Penticton
passes near West Kootenay Power’s main
transmission lines, forcing an emergency
shutdown to protect fire crews working
underneath. This situation results in an
extremely overtaxed Chute Lake reserve
power line. It’s the only remaining line to
the Okanagan and it’s suddenly operating
well over its safe limit. A widespread
blackout seems imminent, and WKP
places an urgent call to Kelowna radio
stations, urging the public to shut off air
conditioners and conserve power. The
crisis is over in less than 15 minutes, as
the Kelowna load drops dramatically in
response to the plea.
December 1996: Victoria is hit with
“the perfect storm”. This is a series of
heavy snowstorms and unseasonably cold
temperatures, and Victoria’s scant snow
removal services are soon overwhelmed.
A couple of quick-thinking staffers at
CFAX come to the conclusion early that
if they don’t get into the station right away,
by morning there may be no way for
them to get in for their regular shifts. As
a result, CFAX is staffed when it becomes
apparent to everyone else that the city is
paralysed. CFAX opens its phone lines to
the public, and quickly becomes a clearing
house of problems and solutions for
an anxious public. For instance, medical
staff needing transportation to hospitals
are connected with volunteer 4x4 drivers.
Local municipality emergency program
operators later complain that they can’t
get through to CFAX to pass on timely
emergency information because the public
is clogging up all the available phone
lines. But this is quickly cleared up and
they get direct access to the station.
August 2003: A forest fire comes up
Okanagan Mountain from the south, taking
out CIGV Penticton’s transmitter, and
the transmitters of all the commercial FM
Kelowna stations a few days later. CIGV
instantly switches to backup facilities at
the studio. As the danger becomes apparent,
the Kelowna FMs quickly prepare
emergency facilities at an alternate site
on Blue Grouse Mountain, so there are
minimal service interruptions when the
main site is destroyed.
The fire moves on to threaten Kelowna,
and sections of the city are evacuated on
very short notice, with local radio very
much in the picture. When CKOV/CKLZ
studios are in danger of being burnt down,
a fireman is placed on 24-hour duty at
the studio, so that the station can operate
until the last possible moment before
evacuation. Fortunately, that moment
never comes.
Next installment: lessons learned!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada JUNE 2007

ENGINEERING
Loads of fun with quarter-wave
sections and pads
BY DAN ROACH
Everyday magic in RF often relies on
two little tricks—the unusual characteristics
of quarter-wave line sections,
and the universal healing qualities
of attenuator pads. “Don’t leave home
without them.”
First of all, the pad. Put one at the
input of an amplifier, and it improves the
headroom. Put one at the output of an
amplifier, and it reduces the “turn-around
gain” and helps get rid of intermodulation.
Put one in between two amplifiers,
and it improves the impedance match
seen by both. Placed between an amplifier
and antenna, it helps protect the amp
from VSWR damage.
And no matter where you put them,
they’ll help keep the RF shack warm and
inviting on cold winter nights. Sometimes
it seems as if almost anything could be
improved by sliding a few pads into the
system. The only real improvement left
to consider is the pad with gain, the socalled
negative-attenuator, but we’ll reserve
that special case for a future column.
The quarter-wave section is the original
RF transformer. Use it to change impedances,
to split RF power and to join it
up again. It’s also the main component
in cavity filters and traps, including the
traplexer used by television transmitters.
The magic tee and switchless combiner
both rely on quarter-wave sections. At
lower frequencies, a pi- or a tee-section
can look like a quarter-wave of transmission
line.
There are only three things you need
to remember about quarter-wave sections:
(1) If the output of a quarter-wave section
is left open, the input sees a short;
(2) if the output is shorted, the input
sees an open; and (3) any two impedances
can be matched by joining them together
with a quarter-wave section that has a
characteristic impedance that’s their geometric
mean. For those of you that haven’t
already fallen asleep, I have handy examples
of all three.
1. is a bandpass or reject cavity in a can,
say for an STL filter or a module of an
FM combiner. Inside the can is a quarter-wave
stub, shorted to the can at the
top, and open at the bottom. The
input connector attaches to a (broadband)
coupling coil that couples RF
energy magnetically to the stub. At the
quarter-wave frequency, the open at
the end of the stub looks like a short
at the coupling end, and maximum
energy is coupled to the stub. If it’s a
bandpass can, there’s a second coupler
on the other side of the stub that
will pick up maximum energy when
the stub is resonated.
2. is a harmonic trap at an FM transmitter
output. (Not a so-called harmonic
filter, which is really nothing of the
kind—it’s really a low-pass LC filter
consisting of series inductors and
Dan Roach works
at S.W. Davis
Broadcast Technical
Services Ltd., a
contract engineering
firm based in
Vancouver. He may
be reached by e-
mail at dan@broad
casttechnical.com.
shunt capacitors to attenuate all low
frequencies.) The true harmonic trap
is a tee in the output line, with one leg
having a sliding trombone contact for
the centre conductor, and ending in
an open. At the harmonic frequency,
that open looks like a short at the centre
of the tee, and so that harmonic
energy is shunted to ground.
3. is one of those two-bay educational
FM antennas that use a simple tee N
connector for a power divider. If the
two antenna elements are 50 ohms
each, how can that work? Well, if the
tee connector is placed between the
bays, and a quarter-wave line section
is on each side of the tee going to a
bay, and the coaxial cable used for
each section is 75 ohms characteristic
impedance (probably RG-11/U), then
the 50-ohm termination of each element
is transformed to 100 ohms at
the tee. And the two 100-ohm loads in
parallel makes for a 50-ohm impedance,
as seen by the transmitter.
(The geometric mean of 50 and 100 is
70.7 actually, but for our purposes 75
ohms is pretty close). So that 50-ohm
transmitter matches up just fine into
two bays of 50-ohm antenna. You can
do the same thing for two STL receivers
at 950 MHz, working off a single STL
antenna (a tip of the hat to Al Pippin
for mentioning this one): split the antenna
line with a normal N tee adapter,
and run quarter-wave 75-ohm line sections
to each receiver. It makes a handy,
low-cost, properly matched power
divider out of everyday materials.
That’s all for this time!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada MAY 2007

ENGINEERING
History of broadcast audio processing
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
In the beginning, there was audio…
and transmitters had a lot of trouble
with it! Audio levels varied all over the
place, particularly with the large amounts
of live broadcasting done “back in the
day”. And transmitters, especially AM
transmitters, really don’t like that.
Bell Labs responded by developing the
ubiquitous VU meter, still with us after
almost 90 years. Broadcasters strove to
make various devices to control audio,
with varying degrees of success.
Somebody noticed that some announcers’
voices display a remarkable
amount of asymmetry. In an age when
broadcasting was inherently symmetrical,
this could have been a job liability for
announcers, but instead Leonard Kahn
invented the Symmetra-Peak©, which
smoothed out audio and made the positives
and the negatives equal but opposite.
Len also started the long tradition of
dipping chunks of his invention in potting
compound (to keep them from prying
eyes, and maybe to add an impressive heft
to his product) a practice that lives on to
this day in audio processing.
CBS Labs finally solved the level control
problem for all intents and purposes,
with the two-box “Max” twins: the
Audimax© gain-rider for the studio, and
the Volumax© peak limiter at the transmitter
site. The year was 1975, and our
problems were all essentially solved… or
so it seemed.
Robert Orban took a look at the FM
program chain, and discovered there was
a great deal to be gained by combining
the low-pass filters, the audio limiters and
the stereo generator into one box, which
he called the Optimod©. He split the
audio into two bands to better deal with
pre-emphasis loudness issues. No longer
would excessive high frequency content
cause overall levels to drop.
AM broadcasting became asymmetrical,
and it became legal to modulate
125% positive, but only 100% negative.
Volumax© solved this by adding a peak
detector and a relay to reverse polarity and
make sure the big peak was always on
top. It was time to torch the Symmetra-
Peak©, and hire back all those out-ofwork
asymmetrical announcers, and
maybe contemplate surgery for the nowunfortunate
symmetrical ones to make
them louder on the radio.
Next came Mike Dorrough. He had
the brainwave of splitting the audio into
frequency bands, processing each separately
and then joining ’em together again.
All of a sudden, everything got a lot louder,
and brighter, and better—if we could
just figure out what to do with all those
extra controls on his Discriminate Audio
Processor: the DAP©.
Mike started with three bands, but
before you know it, others had as many
as 10 or 12, and things got a little out of
hand. But if the processing was adjusted
properly, a bass drum couldn’t “punch a
hole” in the audio anymore.
Not content to take advantage of
natural asymmetry in audio, Circuit
Research Labs put phase scramblers back
in the front end of their processors (the
Symmetra-Peak© rides again!), and added
adjustable asymmetrical clippers at the
output. Again, this made everything a
wee bit louder.
Texar introduced the Audio Prism©,
which introduced a gated “dead band”
into audio compression… instead of continuously
raising and lowering gain
around a threshold, the Texar had a neutral
zone for each frequency band, allowing
us to cling to existing levels until
they were out of range.
On the FM side, Eric Small of
Modulation Sciences started clipping the
output of the stereo generator to create
even more loudness. Others tried to copy
his composite clipping approach, perhaps
with a little less attention to what was
happening to the stereo pilot, and all
hell broke loose for a while. Eventually,
it was learned that you had to do your
clipping first and add the pilot later.
Just as we had reached what we
thought was the pinnacle of audio processing,
digital technology came along
and set everything on its ear again. Now,
we have latency, aliasing, sample rate and
dithering to consider as well. And if there’s
any bit-reduction along the way, make
room for psycho-acoustic masking, noiseshaping
and of course, more latency.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada APRIL 2007

ENGINEERING
Daring Dolby tackles TV loudness
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
We’ve intermittently used this
space in the past to discuss the
problem of raging audio levels
over broadcast television. Whether the
problem is caused by a global conspiracy
of producers of super-loud commercials,
a cabal of broadcast engineers that just
can’t get all the machines to output the
same level, or a bunch of moviemakers
that want to blast the crap out of your
woofers during the shoot ‘em up for maximum
dramatic effect, the advent of digital
delivery systems doesn’t seem to have
helped … actually the problem seems to
be getting worse.
One of the interesting technical papers
presented at last fall’s WABE convention
was from Dolby Digital Labs, discussing
some of their efforts to rein in HDTV
audio levels using metadata embedded
in the digital bitstream. It became apparent
that Dolby has done a lot of research
and thinking about audio levels, and how
to control them without destroying the
program producers’ efforts to achieve a
specific dramatic effect.
The Dolby approach centres on the
viewer adjusting her audio gain to get a
comfortable level for spoken word programming
in her environment. In essence,
by so doing, she is calibrating the
receiver level for what is to follow, and
audio processing upstream will be set to
tell the receiver how many dB above or
below that reference level the current
audio level should be.
Well, I say hats off, as far as that goes,
but there are still a couple of gaping
related loopholes.
First, we can all appreciate the 100dB
or so of dynamic range afforded by the
digital streams. Mostly we don’t want that
much when we’re watching TV in our living
room, particularly if we share walls
with neighbours. While getting that reference
level set by using conversations
is clever and intuitive and, according to
Dolby, it’s also quite accurate (generally
within a couple of dB).
But the reference level is only half of
the problem. Their idea is that the audience
can tolerate levels x number of dB
above that reference for explosions and
shotguns, etc. I can’t help thinking that
the individual viewer might want to have
some say in the value of x.
But the greater problem is that the
metadata setting is in the hands of the
program producer, and as far as I can see
this is on the honour system, which frankly
hasn’t served us very well so far. If
an (unscrupulous) commercial producer
wants to crank the level for his audience,
he now has a new handy tool with which
to do that (the metadata control), with
consequences probably greater than with
the old analog system… because in the
HDTV world there’s little or no processing
downstream to try to moderate levels
even a little bit from source to source.
I’m left with the sinking feeling that
this system belongs in the same world
where the producers of music CDs don’t
clip, compress, equalize and distort their
CD masters to achieve maximum loudness.
This imaginary world sounds like a
good place to live, but it bears little resemblance
to where we are right now.
But maybe I’m selling Dolby’s cleverness
short.
At the same time that they’ve been doing
all this research and marketing at the
broadcast end, they’ve launched Dolby
Volume at the set manufacturers. Dolby
Volume is a new proprietary DSP chipset
to be installed in television receivers. It
will do to audio levels what Dolby
ProLogic did to surround sound: it will
analyze the audio (analog or digital) and
adjust levels to prevent those commercials
from sending us diving for the
remote while making quieter passages
audible.
This is a brand new product so of
course we haven’t heard it yet, but the
reviews have been encouraging. The demonstration
that was reviewed allowed
for differences between TV channels of
30dB or so, yet there was no jarring transition
between them.
And, depending on how clever the
chips are, it may preserve the illusion of
dynamic range. Maybe that’s the best we
can hope for…
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Fable of a farad
BY DAN ROACH
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd.,
a contract
engineering
firm based in
Vancouver. He
may be reached
by e-mail at
dan@broadcast
technical.com.
Of all the various electronic components,
capacitors seem to come
in the greatest variety of sizes
and shapes, perhaps because of the shortcomings
of each type. Correct capacitor
selection, both in original circuit construction
and for repair replacements, can be
vital for proper device performance.
Aside from proper voltage and current
ratings, and physical size and shape,
capacitors can be distinguished by their
dielectric material. It’s the dielectric that
largely determines the capacitor’s characteristics.
Let me show you what I mean: if you
need a filter capacitor for a power supply,
you might need a unit of a few hundred
microfarads, with good current carrying
capacity. Most likely, just because of issues
of size and weight, you’ll end up with an
aluminum electrolytic capacitor. Be sure
to pay attention to the amount of current
cycling in and out of the capacitor, as well
as providing for some voltage margin.
As far as packaging is concerned, be
aware that manufacturers are stressing
radial capacitor production, so axial lead
units are getting harder to locate, and
their prices are running up quickly.
Now your electrolytic cap packs a lot
of capacity in a small space, but performance
is generally optimized for 120 Hz
or so, the internal resistance and inductance
may be quite high, and the device
is generally unipolar. So-called computergrade
electrolytics allow higher circulating
ripple currents and offer lower equivalent
series resistance (ESR).
An electrolytic cap is fine for a DC
power supply filter; not so great if RF or
transient performance is important. And
its value isn’t stable, so forget about using
it in a tuned circuit of any kind. Dipped
tantalum and solid tantalum caps are similar
to aluminum electrolytics, but offer
some performance improvements in density
and ESR.
The oil-filled capacitor uses oilimpregnated
paper for a dielectric, often
in a metal can outfitted with leads. These
are used where you’d like to use an electrolytic
cap, but can’t because the voltage
is too high or you need an AC device
(phase delay for AC motor windings, and
power factor correction for AC motor
loads, to offer two examples).
You should assume any of these
manufactured before the mid-80s is
impregnated with PCB-bearing oil, and
so must be tagged and disposed of properly
upon failure in order to avoid legal
and environmental issues. Their modern
replacements look similar but use mineral
oil or mylar in their dielectrics to
protect the environment from dioxins
and furans.
Ceramic or monolithic caps are small
and inexpensive, and good for non-critical
bypass and filter applications. Often
you’ll find them in parallel with electrolytics
in power supplies, to smooth
out transients that are too quick for treatment
by electrolytics.
But their stability can be even worse
than the electrolytics, so you can’t use
them in any precision applications. An
exception is the so-called plate ceramic
cap, which is quite stable, but 99.9% of
ceramic caps shouldn’t be used when
you’re timing or tuning.
Polystyrene and polyethylene caps
do offer precision and stability, but they
can be bulky and are, by their nature,
inductive. Good for tuning, but not at RF
frequencies. Mylar and polyester caps
can be used for moderate precision, and
they offer good stability and fairly low
inductance.
The granddaddy of stability for capacitors
is the silvered mica cap, which is
great for RF and precision applications,
but you may find it quite expensive and
hard to obtain.
Of course, in broadcasting, we often
run into high power RF applications,
and so we use a few types of capacitors
that aren’t seen much elsewhere—there
are high-power versions of the ceramic
and mica caps. And then there are the
vacuum and vacuum-ceramic types—the
only types even more expensive than silvered
mica.
Often an RF capacitor can be improvised
out of available materials for a particular
use—the so-called plate blocker in
a tube transmitter is often a Teflon or
Mylar sheet, used as a bypass capacitor at
the plate of a PA tube to shunt parasitics,
harmonics and other electronic miscreants
and troublemakers to ground right
at their source.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Batten down the hatches,
winter’s on the way!
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.com.
At this time of year, it’s always a
good idea to go over the transmitter
site and make sure everything’s
in readiness for the winter storm season.
You’ll sleep more soundly next time the
weather report calls for high winds and
miserable conditions.
First off—the genset.
At the very least, this is the time of
year to top off that fuel tank, while the
fuel truck can get to the site more easily.
Might save you having to get the snowplow
out to clear the road so you can
fuel up later, and so prevent one job from
turning into two.
This is also the time of year that I like
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to get the genset maintenance done, so
that if there’s any extended running time
during those storms, we’re as prepared
for it as we can be. Even if you don’t get
overall genset maintenance, it’s prudent
to check the genset battery as well. And
just because the battery will crank the
genset on a warm day, that doesn’t mean
it will start the genset on a cold winter
morning—check the installation date!
Change ’em after five years!
A quick but careful look around the
transmitter building can also pay you
back. You want to make sure that any
roof scuppers are clear, and there are no
signs of water leakage. This may be your
last good chance to take care of any roof
problems until spring.
While you’re poking around, this is
also an excellent time to check over the
ventilation system. All belts in good shape,
all bearings lubricated? If there are manual
controls to recirculate transmitter heat,
now is a good time to set them to their
winter positions.
For AM sites, don’t forget to wander
out to the tuning huts and check them
out as well. It can be a whole lot easier
and more pleasant to do this on a dry
autumn day than when the field is hipdeep
in snow.
While you’re out there, if there’s any
auxiliary heat needed to keep those
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www.hpservices.ca
hps2@rogers.com
contactors working in the cold, you’d
better check that out too! If the site has
security fencing, this is also a good time
to examine the perimeter of the site for
signs to make sure that everything’s secure.
And Industry Canada will be pleased
with you if you make sure that all your
Safety Code 6 signage is still in place.
We’ve found that there is a segment of
the general population that seems to like
to collect these signs as souvenirs.
With darkness coming sooner each
day, this is also the time to make sure
your yard lights are all working as well.
And if you’ve got lights on photocells,
you need to check ’em out.
Scrap metal prices have jumped to alltime
highs, and nowadays there are more
folks that will try to remove anything
metallic, particularly aluminum and copper,
that they can. Keeping the property
well-lit is an easy way to try to reduce this
kind of casual theft, but it only works if
your lighting is functioning properly. It
also makes things a lot more pleasant if
you do end up working at the site in pitch
darkness in the months to come.
This suggestion may seem obvious,
but past experience has proven that it’s
not—if you’re lucky enough to have a
landline at the site, you should check it
from time to time to see that it works
properly. How often we find out that a
telephone circuit has failed, only when
the remote control has an alarm condition
and is trying in vain to call us?
This is the time of year that the fire
department tells us to replace our smoke
detector batteries, and it’s also a good idea
to check your UPS batteries. Once again,
a good gel-cell will last three or four
years… the cheaper ones even less. Any
gel-cells older than that should be
changed on sight.
And more and more of the newer
solid state transmitters and remote control
systems have batteries buried in their
logic boards as part of their memory circuits—don’t
forget to freshen those as
needed.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
I, Bach! U.S. broadcasters
try reinventing radio
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works
at S.W. Davis
Broadcast Technical
Services Ltd., a
contract engineering
firm based in
Vancouver. He may
be reached by e-
mail at dan@broadcasttechnical.com.
Something very strange is going on
south of the border. U.S. FM stations
are falling all over themselves to
upgrade their facilities to IBOC. And the
great majority of them are adding HD2
(and sometimes even HD3) channels to
their carriers as well.
Hmmmm…
Let’s face it, in spite of all the hype at
NAB and elsewhere, IBOC has been with
us (or more properly, them: the U.S. radio
broadcasters) for a while, now. And while
Ibiquity has offered tweaks here and there,
we haven’t seen a wholesale change in the
technical quality of the offerings in the
last couple of years.
About the last thing to happen—originally
touted as the Tomorrow Radio project,
then as HD2—was the cleaving of
the FM IBOC digital stream to offer additional
channels. These additional channels,
which have no analog support, can
be simulcasts of other services (such as
an AM sister station), or even something
completely unrelated.
And most of the new ones seem to be
just that—unrelated.
In the immediate Seattle area, for instance,
there are now 21 IBOC FM stations
on the air. Of these, 15 are transmitting
HD2 signals (one is dabbling with HD3!).
Only two of the HD2 signals are simulcasts
of local AMs.
Well, I have been very sceptical of all
this. To my ear, “full spectrum” IBOC
quality is pretty marginal, and to split it
into two or more channels is to seek parity
with AM IBOC, which still sounds
dreadful. Obviously, there are many folks
out there who disagree.
A vocal group of manufacturers have
been pushing for the extra channels to
be used to make a standard for surround
sound broadcasts, which strikes me as just
silly, both because of lack of appropriate
source material and because of the attendant
loss of sound quality overall. This,
to my mind, would not be progress.
There are still very few IBOC receivers
on the market, and only a fraction of them
can pick up the HD2 signals, since that
development erupted after the Ibiquity
standard had already been “set”. And
IBOC receiver sales have been very, very
limp, so far.
So, just what is going on here? Is this
a panic reaction to the continuing hype
of satellite radio? Is it a response to the
iPod phenomenon? Is it another case of
U.S. stampede response to an opportunity
offered in the “free marketplace”?
Or, more altruistically, is this an effort
to boost early IBOC receiver sales by offering
something not available in analog,
but as a service that you don’t have to
pay extra for? (Contrasting with XM and
Sirius.)
Or is it all of the above?
Most importantly, could all this be
about to happen to us here in Canada?
Well, maybe, I guess.
In our analog world, we have a name
for a second channel that has no main
channel support. In the States, they call
it SCA. We Canucks call it SCMO. And
it’s been around for almost as long as FM
stereo.
And, with some notable exceptions, it
has been dying a very slow death across
the land.
You’ll say that the sound quality of
SCMO wasn’t good enough, or that the
service wasn’t available in stereo. To state
this is to forget that there were no “cast
in stone” standards for SCMO, and there
were alternative modulation schemes that
offered more bandwidth and higher quality,
at prices that were still far below what
IBOC is now asking… but the companies
that offered them went out of business.
From lack of business, one suspects.
Maybe they just weren’t “digital”
enough. That buzzword seems to be able
to work miracles in consumer circles,
even when the actual quality of what’s
on offer is apparently absent.
Maybe there’s a lesson in marketing
for Canada here. Maybe if, instead of
offering “replacement technology” we’d
offered alternative programs on DAB, stuff
that you just couldn’t receive any other
way, then maybe we’d be up to our armpits
in DAB receivers today.
Or maybe it wouldn’t have made any
difference. Perhaps the time just wasn’t
right.
But perhaps it is, now…
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Remote controls we have known
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
One broadcast device that sure has
changed its look and function
over the years is the broadcast
transmitter remote control system. A little
while ago, I had a very pleasant
conversation with Andrew Mulroney,
Comlab/Davicom’s self-described “resident
Newfie”, about remote controls
past and present, and some of the trends
that he sees in up and coming remote
control systems.
Prior to 1955, there was very limited
call for transmitter remote controls in
Canada because you had to have someone
physically at the transmitter, operating
it, at all times that it was on.
After 1955, our remote control system
bible was the Department of Communications
Broadcast Procedure 6,
which spelled out the technical requirements.
Even then, an “Unattended Brief”
needed to be filed with and accepted by
DOC in each case before remote control
operation officially began.
The first remote controls were pretty
horrible, limited as they were to the
technology of the day. Most of the early
units had telephone dials for selecting
control channels, and stepper relays for
jamming at the transmitter end. It’s hard
to imagine any of these Rube Goldberg
devices functioning reliably.
But as technology improved, the
equipment available rapidly got better,
too.
While BP 6 set out what the Department
was looking for, the hardware available
generally was guided by what the
FCC in the U.S. wanted, and so there were
some features and functions included that
our (relatively) relaxed regime didn’t
strictly require. That, incidentally, is why
so many older remote control systems
wanted to operate in “fail-safe” mode, in
such a way that if direct communication
with the site is not continuously maintained
the transmitter would shut down
automatically, taking you off the air.
Well, that’s one way guaranteed to get
someone’s attention!
The need for a direct connection between
transmitter and studio mandated
the use of telco lease lines or radio circuits.
The next big change was driven by
changes in the way that radio stations
operated: BP 6 required monitoring and
control of the transmitter’s output at the
“control point”, which inevitably was
master control. But the advent of satellite
radio networks and local automation
systems meant that more and more radio
stations were not staffed around the clock.
That, and great improvements in transmitting
equipment reliability, resulted in
the need to re-draft the regulations, and
Industry Canada responded with relaxed
monitoring requirements in a new technical
guideline.
The next generation of remote controls
was smarter and used dial-up connections,
so that they could call the station
engineer on his pager or cell phone, wherever
he chanced to be, when problems
occurred at the transmitter. This solved
the problem of the unstaffed control point
back at the studio.
Sigh! More freedom for broadcasters,
less for engineers!
As systems get smarter, they’re showing
increasing flexibility and local decision-making
ability: today’s systems tend
to monitor many more things, and can
take more of an active role in sensing various
failures and taking direct action to
restore service, then advising engineering
staff what has happened “after the fact”.
Being computer-driven, remote controls
have a natural affinity to PCs, and
fax machines, and communications equipment
generally.
Once again, developments south of
the border are having an effect, too: IBOC
transmission requires an active Internet
connection at the transmitter site. As a
Being computer-driven, remote controls have a natural
affinity to PCs, and fax machines, and communications
equipment generally.
result, more and more U.S. broadcasters
are finding themselves with IP connections
at their sites, and they want their
control systems to be IP-enabled as well.
Reduced technical staffs need more
and more automatic logging of events,
both for record keeping and as an aid to
troubleshooting, and today’s control systems
lend themselves very well to that
function, too.
So much so, in fact, that one of
Davicom’s latest efforts has been to allow
the end user to customize what changes
should be logged, because reporting every
item can generate reams of text from a
single event.
With all the new control features and
options, it’s easy, but dangerous, to forget
the basics, though: Andrew reminds
me that it’s still just as necessary as ever
to make a good ground connection to
any unused analog input return lines, or
the potential for trouble in high RF fields
will still combine with that law of
Murphy’s to bite you in the you-knowwhat!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
NAB has come and gone…
(do dah, do dah)
BY DAN ROACH
The throng still seems very confident
that will happen “in just a few months”.
Sorry, but this refrain sounds an awful lot
like what we heard when everyone was
installing AM stereo and, later, Eureka
DAB. And, in both those cases, the receivers
never really did show up.
Oh well, maybe third time’s the
charm?
this is the first step toward one of these
big fish eventually swallowing the other;
opinion seems to be evenly split at this
point over who would be more likely to
swallow whom… will that be a Nautelental
or a Continautel?
Sounds catchy either way!
❖ ❖ ❖ ❖ ❖
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
Once again we’ve beaten the odds
and survived that annual bacchanalia
of broadcast equipment
and salespeople: the National Association
of Broadcasters’ exposition in Las Vegas.
Every year the show gets bigger, and
every year I wonder how that can be. It’s
a time of sore feet and backs, and of
watching some very smart people attempt
that elusive alchemy—of transforming
the products they have into what the customer
thinks he wants, at least for as
long as it takes to get the purchase orders
signed.
❖ ❖ ❖ ❖ ❖
If last year was the year of IBOC transmitters,
this was the year of waiting for
those receivers to turn up at your corner
store.
❖ ❖ ❖ ❖ ❖
The IBOC transmitter race in the U.S.
has led to some interesting new applications
of technology that we may see used
north of the border very soon, whether
or not IBOC makes it through customs.
I’m talking about FM cavity filters—
very sharply tuned and very small—used
stateside for combining external IBOC
sideband signals with an analog FM transmitter
output for the main channel. I’m
talking about circulators that are designed
for FM frequencies and can handle powers
of 10 kW and beyond.
And who says you can’t teach an old
dog new tricks: I saw a couple of new FM
antenna designs, very omnidirectional
and very broadband, intended primarily
for backup sites with multiple, perhaps
agile, frequency inputs.
While they’ve been developed for
IBOC, some of these new products and
ideas will have application to traditional
means of broadcasting as well.
❖ ❖ ❖ ❖ ❖
MERGERS (AND ACQUISITIONS)?
The first day of the show, Nautel and
Continental Electronics announced that
they have agreed to trade and market each
other’s transmitters, after quickly stamping
their own name on the front. They’ll
each service and support the transmitters,
too. There was even a Nautel FM transmitter,
stamped “Continental,” on the
floor at the Continental booth.
Some wags have been wondering if
I’ve had only a few minutes to peruse
the proceedings, but my eye stopped at
an interesting paper that further discusses
the problem of effective audio level control
for television, especially digital television:
as you may have noticed, a topic
near and dear to my heart. It touches some
of the same material we’ve been chattering
about here, but with some interesting
statistics and further data.
❖ ❖ ❖ ❖ ❖
And finally, I got a quick note from the
very distinguished John S. (Jack) Belrose,
Radio scientist Emeritus Researcher of
the Communications Research Centre,
Ottawa, to mention that Canada finally
has a Telecommunications Hall of Fame,
with Reginald Fessenden and Alexander
Graham Bell as the first two members on
the list.
Belrose is a renowned Fessenden
expert, and has recreated some of
Fessenden’s experiments, with audio
samples available on the web demonstrating
what Fessenden’s transmitter
sounded like (the words are Fessenden’s;
the voice, actually, is Belrose’s).
He also wrote a chapter in John
Wiley and Sons History of Wireless, which
is an excellent place to read more about
RF’s remarkable life and accomplishments.
My little writeup a few months
ago barely scratches the surface.
The 100th anniversary of Fessenden’s
invention of broadcasting is coming up
this December—where will YOU be on
Christmas Eve?
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
When is new not better?
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
When is the public not well
served by an emerging new
standard?
There’s a new electronic battleground
forming, and it’s for the next standard of
high-capacity DVDs (digital video discs)
and their players. This one’s starting to
look like the old Betamax vs VHS wars,
and when the smoke clears it may well
be that the consumer will be the ultimate
loser.
Those who back-up the data on large
hard drives want a new, higher-density
optical format. The new hard drives are
so large that even at 4.7 Gb per single layer
DVD, many DVDs are needed to completely
back up a hard drive. But to make
a new format fly successfully (i.e. be costeffective),
they need more numbers, and
DVDs for movie playback remain the
number one application.
The movie studios would like to start
again with a new standard, too, but for
reasons of their own they’d like another
kick at the copy-protection can, in an
effort to control consumer dubbing of
copyright material. Not that anybody but
the algorithm creators seriously think that
new copy-protection schemes will remain
secure for any great length of time!
The canard that’s being floated right
now is that the consumer will have to
purchase a new high-cap DVD player in
order to have movie-length HD content
for his/her new DTV. This is not even
approximately true, as we will soon see.
But that’s the start of the argument for
this new standard.
Two mutually incompatible formats
have emerged—Blu-Ray and HD-DVD.
Both replace the infrared laser inside conventional
DVD with a blue laser for higher
resolution. Where the regular DVD can
store 4.7 Gb/layer, HD-DVD offers 15 Gb/
layer and Blu-Ray offers 25 Gb/layer.
HD-DVD naturally enough has some
similarity to DVD, but Blu-Ray is essentially
a reinvention of the old wheel and
is different enough that the prospect of a
dual-mode player that can play either
format is away off in the future, if ever.
A player for CD/DVD/HD-DVD/Blu-Ray
would need four lasers of four different
wavelengths, and focussing at four diverse
depths, for starters. It’s much more likely
that there will be different players for each
of the new formats, and different copies
of software (movies) available until a
winner shakes out, followed by rapid
abandonment of the losing format and
the poor unfortunates that have already
bought into it.
Hey, that’s why it’s called the “bleeding
edge!”
The irony is that this is not even remotely
necessary for consumers. Present
DVDs are encoded with MPEG-2; a simple
upgrade to a more efficient codec such
as MPEG-4 would allow movie-length
HD DVDs without any change in players
except for a relatively simple programming
upgrade.
But can the equipment manufacturers
be made to see it that way?
We’ve already seen what happens
when the manufacturers can’t agree on a
common standard—have you purchased
memory for your digital camera or PDA
lately? There must be at least six different
types of memory cartridge, and several
sub-types.
Is this necessary? Is it in the public’s
interest that so many different form factors
have become available for what is
essentially the same thing? We have compact
flash (types I and II), secure data (SD)
and mini SD, multimedia card (MMC),
memory stick, memory stick Pro and
memory stick Duo, smart media, and XD
In order to cheerfully accept change,
consumers need a clear choice and an
obvious improvement over the status quo,
at the very least.
picture card. All because manufacturers
don’t want to pay royalties for someone
else’s design, and they all want to drive
the bus!
Consumer backlash seems to be the
last hope—for every 20 or so formats that
the manufacturers devise maybe one survives
the first year or two. Consumers,
faced with too many choices, often opt
to do nothing and the new format dies
on the vine. Lest we forget: elcaset, R-DAT,
Selectavision videodisc, laserdisc, minidisk,
quadraphonic (in QS, SQ, and CD-
4 flavours). Soon to join them (maybe):
SACD and DVD-audio.
In order to cheerfully accept change,
consumers need a clear choice and an
obvious improvement over the status
quo, at the very least. Trying to tell consumers
that they need to replace their entire
DVD library and adopt a dubious new
technology isn’t likely to be a hit, even
with so-called “early adopters,” especially
if there is no backward compatibility.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
The many flavours of surround sound
BY DAN ROACH
Last time I was musing that maybe
we’ve made sound processing so difficult
that it may not be possible, as
broadcasters, to “get it right” anymore.
In particular, I was looking at the variety
of formats that Canadian TV stations
need to be able to receive and somehow
“make comparable” with each other, without
spoiling dynamic range and production
effects.
A little further looking-around shows
that the consumer audio manufacturers
are doing everything possible to complicate
matters for us. Here then, is a very
brief—and no doubt incomplete— primer
of surround sound and high fidelity standards
today.
First thing you’ll notice in the stereo
store is that 5.1 as a consumer standard
for home entertainment is already obsolete.
I recently found receivers labelled 6.1,
7.1, and even 8.1.
Where this is going to end no one
seems to know…
Dolby, as a brand name, has become
pretty ubiquitous, but as a technical description
now means too many things to
mean anything much anymore… from
our old friends Dolby A and B and C
(noise reduction standards for audio
tape), we’ve moved on to Dolby Prologic
I and II, and Dolby Digital 5.1.
When discussing surround sound,
however, beware the moniker “Prologic,”
in either flavour I or II: it means DSP
(Digital Signal Processing) black magic,
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and an attempt to synthesize additional
channels from the original mix.
No matter how hard they try, the results
aren’t remotely the same as an actual
multi-channel mixdown, and they’re
bound to disappoint.
Typically, what sounds alright with
one program has all kinds of weird artifacts
with another. The usual artifacts that
I notice are low frequency rumble and
distortion, the disappearance of centre
channel material, phase cancellation of
important sources like voices and narration—that
kind of thing.
Dolby Digital 5.1 was used to describe
the genuine article, but it has since begotten
Dolby Digital EX, which is also
called THX Surround EX, and there’s also
an extended flavour called DTS-ES. These
three are all extensions to the 5.1 standard,
to 6.1, or 7.1, or even 8.1, and
they’re all available in either “matrix” or,
more rarely, “discrete.”
Once again, the “discrete” is the real
thing, and “matrix” involves more DSP
black magic to attempt creation of even
more additional channels where none
were before (but without the Prologic
name to warn the consumer of the DSP
skullduggery).
To mix things up a little more, Sony
is still flogging their Super Audio CD,
and there’s the DVD-Audio standard as
well—and both of these also have 5.1
flavours. These are believed to always be
discrete, but what will happen when
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Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
extensions are wanted for them is anyone’s
guess. Mine would be more DSP
work, which in my opinion would undermine
any effort to offer improvement over
properly-mastered regular CDs.
In the words of one wag, we can at
least be thankful that the original CD
standard was made before we had learned
enough about digital audio to really muck
things up.
Once you have the surround signal
decoded, there’s still the problem of display
so that the operator can monitor and
adjust the audio as needed for consistency.
What with levels, phase and frequency
content, there’s an awful lot of information
to present in a meaningful display.
Even if we limit ourselves to 5.1 channels,
it’s clear that you’re not going to do very
well with a half-dozen VU meters.
The equipment manufacturers have
arrived with a variety of DSP-driven displays,
but so far none have achieved market
dominance. Further, we don’t know
how they’re going to react to these “flexible”
consumer standards that keep on
drifting to more and more channels.
Maybe it’s not too late to come up
with an update on the classic colour organ
for mixdown control!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Searching for the right level
BY DAN ROACH
I’ll start off by admitting that mixing
audio for broadcast is at least as much
art as science.
And I’ll continue by adding that, given
some of the new complexities, there may
be no complete solution to this problem.
Certainly I don’t have all of the answers.
But I think I know where to look for the
questions…
The problem comes in two parts. The
first is to maintain consistent levels between
program sources. The second is to
get the “right” level in a mix, so that voiceover
material is not buried in a music bed,
and conversely such that the bed is not
pushed down to inaudibility.
Part one of the problem mostly applies
to television audio, since in radio we’re
pretty good at scrunching up the sound
so that all sources are much the same
level. But ask any television viewer about
loud commercials, and you’ll find that this
problem is very much alive, and apparently
insoluble, for TV stations.
It’s not so much a problem of peak
levels, but of the density of audio in TV.
Program producers are interested in a
variety of levels for dramatic effect, but
commercial producers are interested in
maximum impact, and heavy compression
is the inevitable result.
How we keep TV listeners from jumping
out of their seats when there’s a break
for commercials has become the elusive
goal. It may be that the only solution is
to run the commercials at a lower peak
level (like that’s gonna happen!).
Part two used to be manageable, but
it’s rapidly getting more complicated. Part
of the problem is that the right level for
that voiceover in the mix depends partly
on the sound level experienced by the listener.
Fletcher and Munsen showed not
only that listening levels affect our sensitivity
to high and low frequencies, but also
our ability to discern distinct sounds.
Producers that mix down at excessive
monitor levels risk having their voiceover
material buried in the background when
the listener hears the commercial at a
much lower level.
Another well-known factor is called
centre-channel buildup. When an audio element
is placed in the centre of a stereo
sound field, its level becomes more pronounced
in a subsequent mono sum
than items placed to the left or right.
This centre-channel buildup can have a
significant effect on the final result. The
problem was serious enough that some
record companies (most notably A&M)
used to issue radio station 45s with a
mono and a stereo side, with separate
mixes of the same tune.
But these factors have been around
for some time.
What’s new in the last couple of years
is that Canadian TV broadcasters are now
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Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
receiving digital U.S. network feeds for
rebroadcast.
Unlike their U.S. counterparts, the
Canadian stations will typically cherrypick
from among the various U.S. feeds
for their content. And the U.S. feeds, aside
from varying video quality, all seem to be
sending their audio in different standards.
There’s Dolby Prologic, MPEG, analog left
and right and of course digital surround
5.1 standards flying around, and everybody’s
level is different. It’s challenging
enough to successfully receive and decode
these signals, without trying to maintain
proper subsequent mixes in stereo and
mono.
For radio, the new twist is automated
mixdown of voiceovers over music. Without
an operator to ride gain over the
music, the voiceover level is at the mercy
of the machines.
All of which goes to explain some of
the wild audio we’ve been hearing on the
radio and television of late!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Be careful what you wish for
BY DAN ROACH
Dan Roach
works at
S.W. Davis
Broadcast
Technical
Services
Ltd., a contract
engineering
firm
based in
Vancouver.
He may be
reached by
e-mail at
dan@broadcasttechnical.
com.
I’ve always thought that our means of
policing the spectrum in Canada was
a heck of a lot more civilized and
grown up, at least as far as broadcast communication
goes, than the way the FCC
(Federal Communications Commission)
works in the United States.
On those occasions when something
was wrong, a friendly phone call from
your Industry Canada inspector generally
got things fixed in short order. The FCC
technique of issuing citations and exacting
fines always seemed a little barbaric
to me, especially since there doesn’t seem
to be any possibility of a dialogue with
the FCC types in the event that, ahem,
they’ve made a mistake.
And the FCC preoccupation with picayune
details like colour burst frequency,
NTSC timing intervals, and even exposed
AM site ground wires (yes, they will fine
for that!) feels downright extreme.
I mean, what hazard, other than that
of tripping over it, does a bit of exposed
ground wire present?
Broadcast site inspections are from a
bygone age. Many can’t remember ever
meeting an Industry Canada inspector,
except perhaps for a NAV/COM checkout
with a new FM transmitter, or Safety
Code 6 Rule enforcement. Aside from
those two areas of interest, Industry
Canada seems to have largely disappeared
from the broadcasters’ horizon.
They always leave me with the impression
that they have other, perhaps juicier,
fish to fry.
Well, the problem with that is that
the broadcaster is now expected to be
self-policing in technical matters and,
let’s face it, some of us are better at that
than others.
Many AM sites have gone for years
without changing patterns, or perhaps
only going to night pattern from 10 PM
to 3 AM.
FM stations, many of which used to
nudge the regs a bit by modulating up to
maybe 120%, are now running up to
150% and even 180%. And while that’s
damned loud, anybody who thinks that
level of modulation doesn’t present artifacts,
and doesn’t cause potential problems
for others, is kidding himself.
And what are we to think of consulting
engineers who will perform and file
a supplemental proof for an AM station
with broken antenna-monitoring equipment,
as if everything was okay? Up until
recently, if a consultant arrived and all
the equipment wasn’t working and calibrated,
he dropped tools and came back
when the patterns could be confirmed
properly. Many consultants included a
clause in the proof, stating that the monitoring
equipment was in proper repair. I
don’t see how they can be including that
clause any more.
We’re in a period of unprecedented
change, and with change always comes
the rule of unintended consequences.
Industry Canada’s hands-off policy to
broadcasters has resulted in an opportunity
for an unscrupulous few to try to get
an (illegal) advantage over their brethren.
In my part of the world, an MMDS
(wireless cablevision) licence was granted
a few years ago. Now MMDS faces
much greater competitive pressures than
formerly, and I can sympathize with these
latecomers to the marketplace. Traditional
wired cablevision, direct-to-home satellite,
not to mention the efforts of the wireline
telephone companies, are making
this a pretty cut-throat proposition.
But rather than trying to run a viable
operation, or handing back the licence to
the Canadian Radio-television & Telecommunications
Commission (CRTC), we
have an operator that is running a sham
company for a few dozen subscribers, and
parking its butt on that valuable spectrum
until it can be repurposed, and probably
re-sold to the highest bidder.
In present times spectrum can be
worth gazillions of dollars. These guys
were granted public airspace to provide a
public service. Is it right for them to profit
in something that belongs to all of us,
by continuing to hold that licence while
making no real effort to operate it?
So you think that can’t happen here?
The CRTC quietly renewed their licence
for another term just last spring.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Stop this paradigm shift,
I wanna get off!
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
I’ve been thinking about the number
of times in the last few years that
we’ve seen a complete new technology
that has come along and shaken up the
familiar.
A statement like that demands an
example.
Let’s take microphones. There was a
time when, if you wanted a high-quality
microphone for broadcast or recording
work, it would be a velocity microphone
with a ribbon inside. Something along
the lines of a 77DX, or even a Model 44.
Mics for rugged applications would
always be dynamic.
Then along came the condenser mic,
in large-element configurations for highend
work (Neumann and AKG, among
others), and low-cost electret versions (e.g.
Sony) for portable use. This led to the
almost instant demise of the ribbon mic,
primarily because the ribbons were always
fragile (ask anyone who has ever blown
into a ribbon mic), while the large element
condensers seem to take a lot of
abuse and retain their original specs.
But the high cost of the condenser
mics meant that there was still market
room for the dynamics.
Something snapped a few years ago,
however. Several new mic manufacturers
came on the scene (Connaught Labs and,
later, Rode), and whether through new
manufacturing processes, or aggressive
marketing, they drove down the price of
the big condenser mics dramatically.
In an interesting marketing move,
AKG introduced a bunch of new condensers
at low prices, while keeping their
traditional lines at the old prices. And
cost-cutters like Behringer appeared, and
now nobody seems to know what anything
is worth in the mic field.
Ribbon models are long gone, and
now maybe the dynamics are headed in
the same direction. Who can tell?
Another example would be in video
camera technology. From image orthicon
to vidicon to plumbicon, each generation
was a further refinement in camera tube
technology, each building on prior experience
with camera tubes.
Then along came the CCD, and 10
years later, they don’t even make plumbicons
anymore.
In 1975, every newsroom had a Model
26 Teletype, soon to be replaced by an
Extel printer (first application I ever saw
of the Intel 4004 processor), receiving
five-level Baudot code via 20mA current
loop from the local CNCP Telecommunications
office. (Talk about obsolescence—
every noun in the last sentence except for
“newsroom” is a thing of the past!)
Of course the teletype printed everything
that came over the wire, and each
printer used up a jumbo roll of newsprint
(and a couple of ribbons) every day or so.
Incredible waste! Every couple of months,
the newsroom would press all hands into
lugging the next truckload of teletype
rolls up into the newsroom.
Well, we did the best we could, without
PCs and hard drives, with our
Olympia manual typewriters and stacks
of carbon paper. And, of course, our cart
machines….
From tubes to transistors to VLSI,
from carts to hard drives, from the
telecine chain and the film gate to the
latest server, by way of quad-head and
helical VCRs and a bewildering variety of
tape formats, we’ve embraced and later
discarded more disparate technologies
than we can shake a stick at. And what
are we left with: a microphone, a chunk
of cat 5e cable and an IP address.
The way to remain sane, in engineering, is to recognize
that, whether we’re talking about radio or television, it’s all
about the programming.
And a transmitter.
For the moment.
The struggle to remain relevant, in an
age when every teenager has his own radio
station on an iPod in his shirt pocket, and
a home PC can store, edit and forward a
week’s worth of video (with or without the
commercials), is the 800-pound gorilla
that the programming department needs
to take on and wrestle to the floor.
The way to remain sane, in engineering,
is to recognize that, whether we’re
talking about radio or television, it’s all
about the programming. It always has
been.
And as station engineers, it’s our job to
provide the interface between the creative
force of the programming department and
the now almost-constant paradigm shifts
wrought by evolving technology. To absorb
the jolts of change and translate them
into symbols that a programmer can (perhaps)
understand.
May we live in interesting times!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Reg Fessenden clears his throat
BY DAN ROACH
Dan Roach works at S.W.
Davis Broadcast Technical
Services Ltd., a contract
engineering firm based in
Vancouver. He may be
reached by e-mail at dan@
broadcasttechnical.com.
The first radio broadcast in history,
and the first voice that ever modulated
an RF wave, was Canadian.
That voice belonged to one of the true
giants of invention of the 20th Century,
and one of the great injustices of our
school system is that he is not known
better. Nevertheless, Reginald Fessenden
had a remarkable life.
While at school, Fessenden decided
that he wanted to be an inventor and
sought out Edison for employment in
1886. Starting as an instrument tester,
Reg rapidly progressed to head of the
department. Edison at the time was very
heavily involved in generation of electricity.
The early machines were finicky and
troublesome at best, and Reg became one
of Edison’s best field troubleshooters,
where he impressed wealthy Edison
clients like J.P. Morgan.
He also met and became friends with
the likes of George Westinghouse, Lord
Kelvin and the Wright brothers. He went
on to become Edison’s head chemist,
where he developed the first flame resistant
insulation for electrical wires.
Lured away by Westinghouse to be his
plant supervisor, Reg was able to make
light bulbs a paying proposition by replacing
platinum leads with ferrosilicon
alloy, which was much more economical
and had a coefficient of expansion that
matched the surrounding glass envelope.
He improved existing telegraph systems
enormously, invented microfilm,
sonar, and a very lightweight internal
combustion engine. The engine was never
developed into a commercial unit, but
Ferdinand Porsche apparently borrowed
heavily from Fessenden’s design when
he built the original Volkswagen motor.
Alarmed by the sinking of the Titanic,
Fessenden invented sonar as a means to
detect icebergs in poor visibility. He was
able to develop it into an effective detector
of U-boats during WWI. He also patented
geotechnical acoustic mapping, an innovation
that later made him quite rich.
But on to radio:
Marconi may or may not have sent
the first wireless signal across the Atlantic
(there has been some debate in recent
years that his equipment wasn’t good
enough to succeed), but Fessenden was
definitely the first to communicate both
ways across the Atlantic.
Fessenden was obsessed with the idea
of transmitting the human voice over
wireless. The skeptics, including Edison,
thought he was crazy.
This was in the very beginning of the
1900s, a good 20 years before vacuum
tubes would come on the scene. All that
Fessenden, Marconi and their contemporaries
had to work with were coils, primitive
capacitors, and whatever they could
make with their own hands in their laboratories.
Thus was born the spark transmitter:
an AC source, keyed to supply
bursts of energy to an LC tank circuit,
which was coupled to an antenna. When
energized, the LC circuit oscillated for a
short time, producing an RF pulse.
It was Fessenden who first realized that
things worked much better if the LC circuit
oscillated at the resonant frequency
of the attached antenna, and he patented
this innovation. And in an era without
diodes, he developed a vastly improved
RF detector, called an electrolytic detector.
(That scoundrel Lee deForest saw the detector,
copied it, and called it his own, renaming
it the “spade detector.” Fessenden
successfully sued his butt off.)
But voice transmission proved elusive.
Fessenden realized that he’d need a
much higher frequency of AC to transmit
his voice (Nyquist’s Law, not yet discovered,
was already in effect). He tried
to get his old friends at Edison’s General
Electric plant to build a high frequency
alternator, a task at which they ultimately
failed. No matter, Fessenden himself
made an interrupter capable of 10 kHz,
and freely gave the information back to
GE. GE’s so-called Alexanderson alternator
would more properly be named a
Fessenden alternator!
Fessenden’s interrupter took the place
of the telegraph key, and provided 10 kHz
pulses to the tank circuit. He then placed
a carbon microphone between the tank
circuit’s RF output and the transmitting
antenna, in the process inventing amplitude
modulation or, more accurately,
pulse amplitude modulation.
Surprisingly, Fessenden’s new signals
were backwards-compatible with
Marconi’s Morse receivers. Can you imagine
the effect that hearing voices and
music (Fessenden’s violin!) had on radio
operators listening to Fessenden’s first
broadcast on Christmas Eve, 1906?
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Alphabet soup for breakfast
BY DAN ROACH
I’m continually amazed at the number
of acronyms, new and old, that creep
into our speech. It’s almost as if we
(and perhaps technical folk of all stripes)
have our own little sub-language. If we
drop enough of these in to our everyday
speech, we become incomprehensible to
all but those that share our vocation. Maybe
even to them, too. Does this make us
seem more mystical and important?
So here’s a glossary of some of the
ones I’ve been thinking about. This is a
game we can all play, and I’m sure you’ll
think of a whole bunch that I’ve missed.
Maybe we can even print up a codebook,
er I mean a handbook, so that others can
follow along. Or maybe not. I wouldn’t
want to ruin the mystique.
HD Radio is the new name for IBOC
(In-Band On-Channel, or alternatively, It
Bothers Other Channels) in the States.
Same stuff, new name. Hey, people, it’s
called marketing. We don’t know what
the “HD” stands for, but its developer,
Ibiquity, has gone on record to assert that
it most definitely is not an abbreviation
for “High Definition”. Of course not. Who
would be silly enough to think that, except
perhaps the general public?
The AM version of HD Radio has so
far been restricted to daytime-only, since
at night it causes undesirable interference,
but there are forces Stateside lobbying
hard to just ignore all that and press on
24/7. And they just might do that. This
could be the end of AM radio in North
America.
Tomorrow Radio is a scheme originating
with NPR (National Public Radio),
also in the States, to allow FM stations carrying
HD Radio to carry two stereo programs
on their digital selves. The primary
would be simulcast on the analog side,
the secondary program would be a whole
new, unrelated program, sort of like two
stations for the price of one. Think digital,
stereo SCA, and you get the idea. It
might also be a plot to get the bitrate of
FM HD Radio down to parity with AM HD
Radio, so all HD stations will have equal
quality audio. But not good quality audio.
There’s only so much you can do with 30
kb/s or so.
Some other folks, led by Axia, want to
use the extra channels for a broadcast format
for surround sound, apparently figuring
that four or five channels of so-so
quality are better than two of fairly good
quality.
MP3 is the destructive audio-crunching
algorithm developed by Fraunhoffer
that allows music files to become small
enough to be Internet-friendly. These days,
Fraunhoffer spends most of its time in
court trying to catch people who have
been using their algorithm for commercial
purposes without paying the piper.
AAC, with or without a “+”, a.k.a.
HEAAC (High Efficiency AAC) is a newer
technique, for really constrained audio
formats, and it may or may not be at the
audio core of HD Radio. Ibiquity isn’t
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcasttechnical.com.
telling, even though they promised the
FCC that they would, and it seems that
no one can make them. It is used for
Internet audio streaming, and my Apple
iPod really wants permission to convert
all my Windows Media files into this format.
It frequently reminds me that I
should want this, too.
DRM usually stands for Digital Radio
Mondale, which is an alternative digital
format that is being used a lot for shortwave
transmission. Sort of like IBOC, but
without the analog simulcast, or the costly
Ibiquity licensing.
Dolby 5.1 is a DSP-induced mystical
way for making surround sound happen.
If you thought it meant five audio channels,
one of them a common subwoofer,
well I understand where you’re coming
from. If you’ve been in an audio superstore
lately, it would seem that the number
of channels just keeps on growing—
already up to seven or eight. No idea
where this will end.
DVB, or Digital Video Broadcasting, is
an MPEG-y, COFDM-type way to transmit
digital video. In Europe, that’s the end of
the story. Here in North America, the
Grand Alliance (remember them?) came
up with ATSC, which does the same
thing, more or less, maybe better, maybe
not, with 8-VSB. So we only use DVB for
DTH satellite television and ENG, and
switch to ATSC for our DTV.
Clear as mud? Then make up some of
your own!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Admitting your susceptance to
my resistance to impedance
BY DAN ROACH
Dan Roach works
at S.W. Davis
Broadcast
Technical Services
Ltd., a contract
engineering firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcasttechnical.com.
If I thought about that title for just a
little while longer, I might be able to
come up with a ribald limerick about
impedance and reactance, susceptance
and admittance. But that may not be as
great an idea as it seemed at first, so
instead let’s carry on!
I think most of us deal with impedance
all the time, maybe to the point that
we’ve stopped thinking about some of the
basic questions. A few columns ago, I
pointed out that our so-called 600-ohm
balanced audio standard apparently originated
when pole-mounted telegraph
wires were re-used for telephone transmission.
An old story tells us that 50- and 75-
ohm RF transmission lines came along
because that’s what you got when you
used standard sizes of copper tubing to
Sept 16-18, 2005
at Horseshoe Resort just
north of Barrie.
Contact Joanne Firminger
for details at 1-800-481-4649.
make coaxial cables. So we owe our selection
of 50- and 75-ohm cables at least
partly to the plumbing industry? More
on that later.
Who amongst us remembers the 230-
ohm balanced “open-wire” transmission
lines that were used before high-power
co-ax became available?
And what do we mean when we say
that a chunk of co-ax is 50 ohms? Some
smart apple is going to reply that means
that’s the cable’s characteristic impedance.
But what exactly does that mean? If you
measure between the centre conductor
and the shield of that co-ax with an ohmmeter,
it will read open circuit, and it will
measure close to that at audio frequencies.
I daresay if you measured its impedance
at a few GigaHertz with a bridge, you
might find that the cable’s impedance was
close to a short circuit.
Well, the reactive components of a
coaxial cable are the series inductance
(L) of the inner conductor, and shunt
capacitance (C) between the inner conductor
and the shield. Then there’s series
resistance (R) of the inner conductor,
and susceptance (S) (very high shunt
resistance of the insulation between the
inner and outer conductor). So if we
look at the whole spectrum of RF frequencies,
there is a broad range where
the characteristic impedance holds true.
And I guess that’s why it’s called the
“characteristic” impedance.
Ignoring the two resistive components,
the simplified formula for calculating the
characteristic impedance is the square root
of L/C. And there are formulas to calculate
impedance based on the ratio of the
diameters of the inner and outer conductor.
Here’s where it gets interesting: in
actual practice, we find that cable attenuation
increases faster with increasing frequency
than the simple L/C formula
would lead us to expect.
This turns out to be because of skin
effect, which causes R to increase with the
square of frequency, until it can’t be ignored
with our simplified formula. The
obvious way to reduce skin effect (and
that attenuation) is to increase the surface
of the inner conductor, by increasing
its diameter. But this will cause the
characteristic impedance of the cable to
drop, so that to pass a certain power of
signal, greater current will be required,
which increases losses due to resistance,
and eventually we reach a point where
we’re not improving anything this way.
By continued experimentation, we
find that there is an optimum ratio of
inner and outer conductor to minimize
cable attenuation, and it’s about 1:3,
which gives us an impedance of… 75
ohms. If instead you try to optimize the
amount of RF power a given size of cable
can safely carry, you end up at about…
50 ohms.
So there you have it: where signal
losses must be minimized, 75 ohms is
your best bet. In transmission, where we’re
more concerned about maximizing the
power we can crank out of our lines, 50
ohms turns out to be the wise choice.
Sometimes it’s reassuring to find out
that some standard is what it is for good
scientific reasons, and not due to the
whims of someone trying to figure out
what size of pipe to connect to your
bathroom.
70 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
String, tacks and sealing wax:
AM transmitters of the future
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at dan@broadcasttechnical.
com.
There I was at the latest National
Association of Broadcasters exhibition
in Las Vegas, looking at the new
offerings in AM transmitters from the various
manufacturers. And thinking about
how, in the last few decades, the TX makers
have taken all sorts of liberties with
the way RF stuff is made, and how, by
and large, they seem to have gotten away
with it.
When I went to school (admittedly
that was more that a little while ago),
there was a great deal of stress placed on
using non-ferrous materials around RF.
Most everything was silver plated. There
were absolutely no sharp edges anywhere.
And it was all made to be 50-ohm, whatever
that meant.
The big transmitter makers of the day,
RCA and Continental for instance, pretty
much stuck to that. And they made a
series of transmitters that worked the way
we expected and, perhaps more importantly,
they looked like we expected them
to look.
After a while you grew accustomed to
big silver-plated coils and hardware, and
neat silver-plated tubing carefully bent in
smooth right angles. Everything built very
big and very imposing-looking, and always
with an eye to mechanical strength.
It seemed to add a level of comfort to the
inner Teuton in the average broadcast engineer.
Certainly the right angle part did.
Well, I like to blame the next chapter
of our story, if blame is the right word,
on Nautel.
It was Nautel that came along in the
early 80s, and replaced RF connectors with
barrier strips and crimp terminals. Nautel
taught us that a couple of strands of
hookup wire, twisted together inside of a
piece of copper tubing, could serve as a
very nice transmission line. Certainly, their
AMPFET 10 transmitter, with its plexiglas
front and it’s relative dearth of meters,
didn’t even look like it was a transmitter.
And so began what I secretly think of
as the Home Depot era of AM transmitter
design. Obviously some new minds, unencumbered
by our old hoary broadcast
engineering methods, were at work in
the factories.
It’s been a slippery slope since, as
other manufacturers discovered that they
could save a buck or two, or streamline
production, or just mess with our minds
by using ‘unconventional’ techniques.
The new Broadcast Electronics 50 kW
AM is a sight: there’s no big iron (it’s all
switching power supplies), and the control
system is chock full of RJ45s and
DB25 connectors to make the IT folks feel
right at home.
The real shocker, though, is the output
matching network—multiple strands
of smallish Litz wire, tywrapped together
on a plastic frame to make a high-power
coil. In lieu of a traditional rugged porcelain
insulator with nonferrous hardware,
a little strip of PVC plastic with a tywrap
on top!
Not to be outdone, the folks at Nautel,
in their new 50 kW rig, have replaced the
homely coil with a rectangular design:
one side of the rectangle is a printed circuit
board, and the other three are formed
by a bunch of parallel copper U-straps,
spaced apart with Teflon tape. You tap
the coil by pushing a wire with an automotive-style
lug on to a mating contact
on the PCB.
Ahem, it brings a whole new meaning
to the term ‘quadrature coil.’ (Sorry,
very bad pun.)
I remember some bad jokes in the
past about AM frequencies being so low
that they’re almost DC, compared to other
bands in use today. Some had even
hinted that, owing to their low frequencies,
AM transmitters shouldn’t be considered
to be ‘true RF’.
Now the transmitter makers are systematically
proving that, in many respects,
that joke was always on us!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
RDBS in your future?
BY DAN ROACH
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcasttechnical.com.
RDS—or as we say in Canada RDBS
(Radio Data Broadcast System)—
is a low-cost technique to provide
many of the value-added services associated
with Digital Radio to existing FM
stations.
Like Eureka DAB, RDS has been
around for a while and has proven to
work as advertised. Unlike DAB, there
are lots of RDS-equipped radios already
available to the public—which makes
some of us wonder why it hasn’t caught
on like sliced bread, at least so far.
RDS is a narrow-band data subcarrier
that operates at 57 kHz, which is exactly
the third harmonic of the 19 kHz stereo
pilot. The 57 kHz carrier is suppressed,
leaving only the data sidebands, which
are typically injected at four per cent or
so of total modulation.
The data provided can be a little or a
lot. At the low end, most stations would
implement scrolling call letters and a station
slogan. RDS can also tell the receiver
what format the station thinks it is, and
can provide accurate time, so receivers
can be programmed to seek, say, country
music radio stations, and always have accurate
time displayed. Many stations like
to add scrolling song title and artist information,
both for what’s playing right now
and what’s coming up after the next stop
set ends.
Some stations in Seattle (where RDS
installation has been quite active) also
put up weather forecast information and
ski patrol info at the same time that
they’re announcing it.
A unique feature of RDS-equipped car
radio/CD players is the ability to set a
data flag when local traffic information
is being discussed on the main channel.
This flag can tell the radio to interrupt a
CD that it’s playing (or another radio
station), switch to the traffic info, then
switch back after the report is finished.
Another DAB-like feature of RDS is
the ability to provide lists of alternate frequencies
where the station may be found
in areas where the primary frequency is
weak or unavailable. The receiver can be
set to switch automatically to the alternate
frequency when this happens. This
would seem to be a natural feature for
CBC/Radio Canada, yet they, too, have
been slow to adopt the technology.
Like Eureka DAB, RDS comes to us
from Europe (France and Germany).
RDBS, the North American flavour, is very
similar to RDS, and receivers equipped
for one standard have little trouble with
the other. The concept seems to be much
more popular in Europe, with the majority
of radio stations and receivers conforming
to at least part of the standards.
One of the few controversial aspects
of the system is whether or not song
information should be scrolling across
the faceplates of car radios. Expressly forbidden
in Europe, it is perhaps the most
attractive aspect of RDBS for North
American stations and listeners. The
Europeans fear that the scrolling data
will distract drivers and cause accidents.
Surprisingly enough, we never heard a
similar argument when DAB was displaying
similar features; now that very dynamic
GPS, MP3 and DVD displays also are
on dashboards, the point may well have
been rendered moot.
So why don’t we hear more about
RDS, and why haven’t more radio stations
jumped on the bandwagon? It’s available
to any FM radio station out there, and
the entry-level encoders that provide the
scrolling “static” information can be purchased
for less than $1,000.
Even the more sophisticated “dynamic
RDS encoders” cost only a few thousand
dollars to install. (But it may be quite a
bit more involved to provide automatic
song titling information, for instance, depending
upon your existing automation
system.)
Perhaps the problem is a lack of awareness
of the number of RDS-equipped receivers
already in the market. Although
we’ve heard some estimates of as high as
1/3 of aftermarket car radios being RDSequipped,
very few choose to brag about
it. You’ll see radios advertising features
such as MP3 capability or detachable
face plates, but it can be very hard to find
out if a radio is RDS-equipped without
actually trying it out yourself. This is also
true of factory-equipped radios in new
vehicles.
It’s possible that RDBS, rather than
making a big splash, is going to silently
sneak up on us all, gradually gaining market
share until we’re wondering how we
got along without it.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Gibbled audio in the digital domain!
BY DAN ROACH
Dan Roach works at
S.W. Davis Broadcast
Technical Services
Ltd., a contract engineering
firm based in
Vancouver. He may
be reached by e-mail
at dan@broadcasttechnical.com.
First of all, the good news—the ubiquitous
compact disc was developed
before we knew enough about bitreduction,
digital compression, and general
screwing around with data to come
up with something really terrible. Sixteen
bits per channel, 44.1 kHz sampling rate,
and no compression. Life was simpler
back then, but we didn’t realize how
lucky we were. Digital chaos was just
around the corner.
Now the bad—even with the relatively
pristine CD to work with, record companies
have managed to come up with
several ways to make our lives miserable,
in both the analogue and digital domains.
Today’s CDs are often mastered with
predistortion and clipping built-in, in
(what to my ears is) a misguided effort to
make CDs “louder”. Given a dynamic
range of 96 dB, there’s far too much effort
to keep the peak audio within a hair’s
breadth of the digital ceiling. As broadcasters,
we should all be screaming out
“Hey, that’s our job!” (Tongue firmly in
cheek).
I remember when CDs first appeared
in radio stations: we were mostly concerned
with that huge available dynamic
range, and how to process the audio
effectively for broadcast. Little did we
know, the reality has turned out to be
very different: more often, it’s “how do
we mask the clipping and distortion and
generally crappy audio we’re given to
work with?”
Highly compressed and clipped CDs
are just the beginning…
It is a very rare radio station that is
able to resist the constant flow of MP3
files on to their local server, both for
commercials and produced content, and
sometimes even for music. Like all the
new bit-reduction algorithms, MP3 isn’t
a single standard so much as it’s a suite
of standards, applied at various bit-rates
in varying degrees by diverse operators
with different goals and very different
sets of ears. To say that the quality is variable
is a dramatic understatement—it’s
all over the map!
Compounding the problem, most stations
still have bit-reduction techniques
somewhere along their program chain.
These techniques are optimized and intended
to work with what has become
a very rare bird indeed, “unprocessed”
audio. Whether the bit-reduction is MPEG
for the storage system, or apt-X for the
STL, it’s not really meant to work on audio
that has already been compressed and
limited, let alone clipped or bit-reduced.
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The result, to a varying degree, is the
creation of artifacts—new, unexpected alterations
to the audio, whether it’s a flanging
effect, a distorted drumbeat, or even
a weird spatial effect. Even without additional
bit-reduction, however, our analogue
and digital processors are also
meant to work on “unprocessed” audio,
and can react surprisingly when presented
with bit-reduced waveforms.
The digital frontier has taken away
our old headaches and, hydra-like, replaced
them with a whole host of new
ones. We no longer have to worry about
tape head alignment, cleaning and wear,
and turntable stylus damage. High frequency
roll-off is no longer a worry. What
we have to grapple with is inconsistent
quality between sources, and artifacts that
come and go as program files change. To
make matters worse, the old problems
were measurable with test instruments;
the new ones are “psycho acoustic,” and
hard to measure in a meaningful way.
In the analogue era, part of the solution
to the consistency problem was the
multiband processor, which gave us controls
that tended to draw diverse sources
together for a more uniform sound. It is
ironic that the same processor is now a
big part of the problem.
What can be done? Distressingly, very
little. The makers of Orban and Omnia
processors have lately been aggressively
meeting with the folks that master CD
recordings, trying to educate them to the
problems that heavily processed music
will present to the broadcaster. Good luck
with that!
In the same vein, you can try to talk
your music department in to not accepting
MP3 files as source material. I don’t
know that we can stem the tide of MP3s
in commercial production, but maybe
you can have a talk with your production
department too, about vetting the files as
they come in, and asking for better copies
of the worst offenders.
Most of us thought that digital audio
was going to take essential quality issues
off of the table. Surprisingly, a set of critical
listening ears has never been more
important to the broadcast engineer.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
More on quartz
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
Last time we got together we were
discussing quartz crystals, Nazis and
the jungles of Brazil. This month,
the more prosaic details of series and parallel
resonant crystals, SAW filters and
ceramic resonators.
If you’ve ever ordered a crystal from
a manufacturer, you’ve discovered that
there’s a world of difference between the
free and easy theory of what crystals do
—plunk one into a circuit and it controls
the frequency—and actual practice, which
revolves around series or parallel models,
different cuts, drive level, load capacitance,
tolerance and operating temperature. For
a two-terminal device, the quartz crystal
sure can get complicated in a hurry.
A crystal’s oscillating frequency drifts
ever so slightly with temperature, so in
order to tighten tolerances, they’re often
made and calibrated at an elevated temperature.
That way, they can be operated
in a temperature-controlled oven, and the
variance due to changes in ambient temperature
is removed. Tolerance is just a
quality-control or calibration issue… obviously,
the more accurate you want your
crystal to be, the more you’re going to
have to pay. Different cuts have different
characteristics, but 99% of the crystals we
see in communications are AT-cut, so at
least that’s one specification that’s easy
to deal with. Drive level doesn’t matter
very much, but if you overdrive your crystal,
you may damage it.
Series resonant crystal oscillators are
simpler than their parallel brothers, but
there’s a price for simplicity—you can’t
trim the frequency to get exactly what
you want. And most series resonant oscillator
circuits will “take off” and still oscillate
without the crystal… at a frequency
more or less of their own choosing.
The parallel resonant circuit is a bit
more complicated, but it is better behaved.
It can be made to shut down if
the crystal isn’t plugged in. And it can
have a small reactance added to “pad”
the frequency up and down a bit: maybe
100 Hz per MHz of oscillating frequency.
In either case, the crystal is much the
same, but it is specified differently. Remember
from last month that a crystal is
much like a series R-L-C circuit, where L
and C are motional reactances, and they
resonate at a frequency. This frequency is
the series resonant crystal frequency.
A parallel resonant crystal will be cut
to a slightly lower resonant frequency (offset
below the desired frequency a bit), but
will be specified while operating into a
particular capacitance, which will always
act to increase the frequency. This load
capacitance is the effective extra capacity
that the crystal sees externally between
its two terminals. Sometimes you have to
calculate a bit, using the formula for series
capacitors, to figure out this value. But it’s
essential if you’re trying to order a parallel
resonant crystal. If you try and use a
series resonant crystal in a parallel circuit,
it will always be too high in frequency.
Padding just speeds the oscillator up more.
Radio amateurs figured out a long
time ago that quartz crystals of similar
frequencies can be hooked up in networks
that provide very narrow bandwidth.
The crystal filter was born.
In recent years, ceramic filters, made
by a process similar to ceramic capacitors,
have made IF filters for AM and FM radios
very inexpensive and compact. The performance
doesn’t match the crystal filter,
but neither does the price, either.
One high-priced, high-performance
filter that has come along is the SAW, or
surface acoustic wave filter. A piezoelectric
transducer excites the surface of a plate
of glass that has been etched with aluminum
traces in a such a way that some
frequencies are reinforced, others are cancelled
out. Since acoustic waves travel
much more slowly than electromagnetic
waves, a small device can be many acoustic
wavelengths long. At the other end of
the plate, another transducer picks up what
is left of the wave and converts it back into
electricity. This is followed by a big preamplifier,
because the transducer losses
will probably be more than 50 dB. Because
thermal expansion would cause the filter
to drift, an oven is likely to be used.
Altogether, a very elegant, very smooth,
high performance filter is possible, with
a price to match!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Nazis sank my crystals!
BY DAN ROACH
Imagine a tuned LC circuit with a Q of
10,000! Incredibly narrowband.
If you wanted it to resonate at a frequency
of 1 MHz, it would need an L of
10 or 20 Henries, and a C of 20 or so fF
(femto-Farads=10-15 Farad)… It would
be altogether not very practical, since any
coil of that size would have tonnes of
stray capacitance and, aside from its bulk,
it would completely swamp out your fF
capacitor.
And yet, there is a way to do it, because
we’ve all seen circuits with Qs like
that…called crystal oscillators!
Quartz crystal manufacturing technology
started development in between the
two world wars, and it’s a fascinating story,
full of adventures and derring-do worthy
of Indiana Jones and his gang. While the
work was driven by the requirements of
the military, most of the discoveries were
made by radio amateurs experimenting
with stuff they really didn’t understand
very well.
The piezoelectric effect started it all
off, back in the 1880s: Marie and Pierre
Curie discovered that there were a few
substances, like quartz and Rochelle salt,
that when given a squeeze would produce
a voltage. Likewise, supply a voltage, and
the crystal changes its own shape.
Quartz crystals are like electric motors
and generators in the sense that they
convert between electric and mechanical
energy. If an AC signal of the right frequency
is applied to it, the crystal will
resonate and start to vibrating. Like any
object in elastic motion, the crystal has
an elasticity and a “reluctance” to change
in motion: the elasticity shows up as a
capacitance, and the “reluctance” looks to
the circuit like a very large inductance.
These two quantities make up the motional
reactances of the crystal. And the “right
frequency” happens to set up a standing
wave inside the crystal structure, at the
same frequency that the motional reactances
are equal in magnitude and opposite
in sign!
Quartz is a crystal, meaning that the
molecules in a chunk of it are lined up in
a particular pattern. Slicing the crystal at
a particular angle to its geometry produces
a wafer that can be excited in one
fashion or another. The dimensions, primarily
the thickness, set the resonant frequency.
There are special “magic” angles
for the slicing, which can be measured
by x-raying the crystal.
Prior to 1926, all crystals used the X-
cut. In 1927 the Y-cut was found, and in
1934 the AT- and BT- cuts were discovered.
Today’s general-purpose crystals are
99% AT- cut. The different cuts have different
characteristics, including temperature
stability. One of the very first niche
applications for quartz crystals was in the
oscillator circuits of broadcast transmitters.
The U.S. wasn’t yet at war, but things
were looking pretty grim as 1940 rolled
around. If the States entered the war,
they’d need lots of communications sets.
And the two-way radios being developed
needed lots of crystals. At the time no one
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
knew how to make crystal units from
synthetic quartz.
Although natural quartz is common
enough on our planet, the stuff that was
pure enough to be “electronic grade” was
to be found only in one place: in mines
high in the mountains of central Brazil,
above the tropical jungle. As production
increased, a worldwide shortage of electronic-grade
quartz rapidly ensued. Prices
for the raw material doubled, which had
the strange effect of even further reducing
the supply… the Brazilian quartz miners
were only looking for enough money to
subsist, and raising the price just caused
them to quit mining sooner!
Finally a few thousand pounds of the
precious material were obtained and
loaded onto a freighter, bound for quartzhungry
U.S. crystal labs. A Nazi U-boat
sank it as soon as it left the harbour. After
that, all wartime shipments of quartz to
the States were delivered, at great expense,
by government DC-3! (Today almost all
crystal units are made from synthetic
quartz, so Brazil’s importance to the electronic
industry has diminished.)
Next time, we’ll look at some of the
various quartz products used in broadcasting:
parallel and series crystal units,
and SAW filters and crystal filters.
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Fixing the stubborn switcher, Part II
BY DAN ROACH
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcasttechnical.com.
Last time we got the preliminaries
out of the way. Now I’ll try and give
some concrete suggestions on getting
that stubborn switcher back up.
First of all, open the thing up and
make a really close physical inspection.
You’re looking for carbonised parts, blown
circuit board traces (which can range from
traces completely blown away from the
board to hairline cracks that are almost
invisible), signs of excessive heat, tiny
cracks in solder pads surrounding component
leads, cold solder joints, and signs
of cooking and corrosion.
Be sure to look closely at power resistors
for signs of cookage. Be extra vigilant
around the following: electrolytic capacitors
(signs of outgassing and outright
leakage, bulges in the can or perished
rubber seals around the positive leads);
power transistors (carbon traces, broken
leads, carbonising of insulating washers
and holes punched through insulating
washers; and input and output connections
(look for heat fatigue: cold solder
joints, corroded connector pins, and hairline
cracks in solder connections).
Use your nose as well as your eyes.
Trouble is more likely to be found in areas
that get warm in normal use—the high
current areas of the supply, for instance.
If you can’t find physical evidence, it’s
time to start thinking about the circuit and
how it’s supposed to work. Let’s examine
what the power supply is and is not doing:
1) “It’s dead, Jim!” No output voltage, no
input current. Obviously you should
look for blown fuses, on either the input
or output side. Is voltage getting
to the input filter cap? If not, look at
the input rectifier bridge and components
in that area. Usually the switching
transistor stage consists of one or
more power MOSFETs. Look on the
gate terminal. Are pulses getting to
the MOSFETs? If yes, then the power
transistors may be cooked. If no, get
back to the power supply controller.
If it’s not generating pulses, it may be
dead or it may be shut down, internally
or externally (time to check out
those data sheets), or it may be that
its “supervisory power supply” is not
working. You should be so lucky!
2) “Call the fire department.” Very high input
current, low or no output. Well,
here you’re likely looking for a short
in the input or output loop. A currentlimited
variable voltage supply instead
of the regular input connection can be
handy here. And disconnect the load
from the output. When you run up the
input voltage, does the input current
rush up right away, or only after you’ve
gotten close to the nominal input
level? If right away, look for shorted
parts in the input loop; if the troubles
only start once the controller wakes
up and starts pulsing the power transistors,
the problem is likely on the
output side. Have a good look at those
power MOSFETs, and don’t forget the
spike suppressing diodes that surround
them. Or shorts in the output
loop elsewhere—if there’s an overvoltage
crowbar, you should check to see
if it’s acting prematurely. If the crowbar
circuit is controlled by a zener
diode, be especially suspicious. If the
trouble’s in the load, try running the
supply with minimum input voltage/
current and feeling parts in the load
for hot spots. Careful! Even if there’s
no high voltage, the hot parts can remove
skin from your fingertips in a
most distressing and painful manner!
3) “Darn thing works until a load is connected.”
A very common problem. The
supply appears to work properly (input
and output voltages in the right
neighbourhood), but the supply cannot
provide its specified load current.
Look for one of two faults: either the
protective circuitry is shutting down
the controller too soon (overcurrent
sensors tripping too easily), or the output
filter capacitor has dried out and
gone partially open. The few inches of
wire between the power supply and
the load may represent enough inductance
at the switcher’s operating frequency
to prevent proper operation—
location of that output filter cap, close
to the power supply, may be crucial for
the proper operation of the supply.
With a little patience and perseverance,
even the most recalcitrant switcher can
be brought to bay. Happy hunting!
46 BROADCAST DIALOGUE—The Voice of Broadcasting in Canada

ENGINEERING
Switch-hitting your power supply
BY DAN ROACH
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
dan@broadcasttechnical.com.
No matter where you look, nowadays
you’re surrounded by switching
power supplies (or “DC/DC
converters,” to use the latest jargon). Sure,
they’re more efficient than the old linear
supplies, but they really aren’t any more
reliable—the old saw that whenever
equipment fails “it’s always the power
supply” is at least as true today as ever it
was.
The more cynical among us might say
that we’ve traded higher efficiency and
lower power supply temperatures for
more circuit noise and higher complexity.
And it’s pretty hard to argue with that
statement. But, you know, switchers have
been coming on ever since the first television
receiver was built (where did you
think that high voltage for the picture
tube came from?), and they’re not going
to be leaving us anytime soon. So let’s
trade a few tips to make their analysis
and repair a little less imposing…
There are several reasons why switching
supplies can be a real bear to repair.
Firstly, there are often hazardous voltages
involved. And many of these new
supplies play fast and loose with the
notion of “ground”, which adds to the
danger as well as being a pretty important
part of the functioning of our
favourite test equipment, the oscilloscope.
Then, of course, there’s the fact that
when switchers run into trouble they
generally react by stopping. Once they’ve
completely halted, the original cause of
the stopping can be a real puzzler. This is
especially true if the equipment manufacturer
uses the shutdown feature of the
switcher to minimize component damage
under fault conditions… the fault
causing the shutdown may have nothing
to do with the power supply itself.
And the fact is that many modern
switchers are now operating at close to
RF frequencies, which require us to
analyse what’s gone wrong a bit differently
than the old 120 Hz linear supply.
Now, I’m going to try not to be too
ridiculous here and suggest that you
should be repairing any power supply
problem that comes along. You have to
keep an eye on the value of your bench
time, but there are always exceptions.
Your PC power supply can be replaced
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for less than $40, and there’s no way you
can compete with that—just change it
out! On the other hand, I just finished
working on a small switcher, about 60
watts or so, in a microwave radio, which
the original equipment manufacturer advised
me to swap out—at a cost of $2,500!
Often, in transmitting equipment for
instance, the power supply is too big to
replace the whole thing conveniently anyway.
So you have to use your judgement.
First, let’s talk about documentation.
Try and get yourself a schematic of the
power supply. This is pretty vital with a
switcher, because of the circuit complexity—much
more so than with a simple
linear supply.
At the very least, get on the Internet
and try to get data sheets for the power
transistors and switcher controller chips
used in the supply. You’ll need them if
you get to the point where you have to
figure out how the darn thing was supposed
to work!
Switching power supplies come in
several various flavours, and you need to
be especially on your toes if there’s no
input transformer. One of the available
flavours takes the AC line, runs it through
a bridge rectifier and a capacitor, and
rams it into the supply. I hate this type!
Be especially careful in this instance, because
there is no ground reference on the
input to this type of supply.
It may well be that the output side,
however, is ground referenced! Regardless,
if you come into contact with either
side of the input line, you and/or your
oscilloscope are at risk.
Your best bet when dealing with this
configuration of power supply is to get
yourself an isolation transformer, so that
you can ground one side of its output,
and feed the supply under repair with
this. An isolation transformer fed by a
variac is even better. Of course if the supply
happens to be fed by three-phase
208 VAC, this may not be practical.
We’re just getting started, and already
I’m out of space. More on the innards of
recalcitrant switchers next time.
46 BROADCAST DIALOGUE

ENGINEERING
Mysteries of the
shielded loop revealed!
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
There are a variety of antennas that
you can use for AM reception at the
studio: many engineers have used
a whip antenna, usually mounted on a
ground plane. I’ve seen automobile antennas
used in this way.
Some favour a longwire antenna, but
I’ve always preferred the shielded loop.
It’s easy and inexpensive to make one, and
although they’re not particularly sensitive,
their unique noise- and interferencecancelling
properties mean they can give
surprisingly good performance in difficult
situations. How come? As a matter of
fact, once you start to look more closely,
many people start to wonder how come
they work at all! I’ll try to explain their
secrets.
The first question many have—if the
doggone antenna is shielded, how does
it pick up a signal at all? The answer is
surprisingly simple. Our desired RF signal
consists of electromagnetic waves,
which have an electric and a magnetic
component. We shield the electrostatic
component only—and pick up the magnetic
wave. Any grounded conductor can
be used as a shield against the electric
wave—if we had wished to shield the
magnetic component, we’d have to use a
magnetic material, such as iron, steel,
nickel or even mu-metal. And sure
enough, if we use a piece of steel electrical
conduit for our shield, we won’t get
much of a signal. Copper, on the other
hand, makes an excellent electrostatic
shield, without affecting the magnetic
field, so that’s what we’ll use today.
One aspect of that shield that’s bound
to confuse is that there must be a break
in the loop—otherwise the windings
inside will effectively couple to a shorted
turn, and you’ll get little or no signal
coming out. The shield must be connected
to ground or it will be effectively invisible,
and will provide no shielding action
at all. Depending on the details of construction,
it may be desirable to switch
the ground connection to the shield on
and off, allowing the antenna to serve as
a shielded or unshielded loop.
Since, in its shielded form, the loop
is picking up only half of the electromagnetic
wave, that explains why its sensitivity
is a bit low. The surprise is that
the received noise is usually attenuated
even more, and that’s because most electrical
noise is electrostatic in nature. An
added bonus is that the rejection nodes
of a well-constructed shielded loop are
very deep—perhaps 25dB! (Incidentally,
this explains why the shielded loop is so
often used in radio direction finders.)
Often, when we’re faced with a situation
involving nighttime interference, we can
benefit by forgetting about peaking the
desired signal, and instead concentrating
on nulling out the interfering ones.
If you need more sensitivity, you can
resonate the loop by experimentally applying
a small tuning capacitor—no more
than 500 pF or so—in series with the
loop. You’ll know when you reach the
right value—the output level peaks up
quite sharply. One precaution with this
arrangement, though: it is quite easy to
achieve a loaded Q high enough to lop
off the sidebands, which will result in a
loss of high-frequency modulation content,
and distortion there too.
Received signal strength is more or
less in proportion to size: twice the size,
twice the signal. The optimum number
of turns to use is counterintuitive—more
If you need more sensitivity, you can resonate the
loop by experimentally applying a small tuning
capacitor—no more than 500 pF or so—in series
with the loop.
turns does not equal more signal. As a
matter of fact, signal strength drops off
pretty quickly past the optimum number.
This is because we’re typically trying
to match into a receiver front end that
has a fairly low impedance—say 50 to
100 ohms. More than a handful of turns
results in a high impedance device, and
leakage capacitance to the shield starts to
become significant, too.
Flatter results across the broadcast
band can be achieved by using three
turns or so in the body of the loop, and
connecting a balun—a balanced-to-unbalanced
transformer—at the output of
the antenna. This improves the impedance
match and balance, because if you
look at it carefully, you’ll see that the
loop itself is essentially a balanced circuit.
By inserting the balun, you’re providing
the right type of balanced load for
this antenna. Ten turns or so on the ferrite
toroid of your choice, bifilar-wound,
makes a very nice, compact, self-shielding
balun.
So there you have it: the shielded
loop, unplugged!
62 BROADCAST DIALOGUE

ENGINEERING
Rogers to the rescue
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
In the 1920s, radio was still mainly for
the dedicated few.
Radio receivers of the time were large,
clunky, hard to adjust, and heavy … and
aside from “crystal sets”, they were all battery-powered.
All receivers used tubes, and
the tubes needed the dreaded “A” and “B”
batteries. (The six-Volt “A” battery was for
the tubes’ filaments; the plate supply was
formed of 45-Volt “B” batteries. And yes,
this is where the name “B+” for the plate
supply came from.)
Then along came Edward Rogers
(senior), boy genius, who brought not
one but two technical innovations to
radio receivers that made them much,
much more accessible to the general
public. And, as it turned out, he was just
getting started.
First, the A Supply. Rogers invented
the indirectly-heated cathode, that meant
that the filaments could be powered from
AC power. Since there were several tubes
needed in the receiver, if you were clever
you could then place all the filaments in
series and power them directly from the
120-Volt mains. Rogers had just effectively
eliminated the need to have an A
supply at all.
Why didn’t someone else try this?
Well, they did, but with the regular
tubes of the day the AC hum from the filaments
would come out the other end of
the radio a lot better than did the intended
signal. Rogers’ genius idea was to
stop using the filament as a supply of free
electrons, and instead use it as a heater
for an electron-generator. His cathode was
a specially-treated sleeve that slid over the
filament heater. By its design, it shielded
the cathode and the rest of the tube from
the AC fields generated by the filament
inside. The result: no hum!
Next, the high-voltage or B supply.
Rogers discovered the rectifier tube, which
had already been invented by others but
not applied to radio receivers. He wasted
no time in showing everyone how to do
this, too.
The result was a console radio, with a
loudspeaker, that wasn’t continuously
draining big, heavy, expensive batteries
when it was being used.
Edward (Ted) Rogers, with his brother
Elsworth, and financial backing from his
father, started the Standard Radio Manufacturing
Company (later Rogers Majestic),
which begot the Rogers Radio Tube Company,
which led to the Rogers Batteryless
Radio Company. In August, 1925, Rogers
unveiled the new indirectly-heated cathode
tubes. A few weeks later, he displayed
the first Rogers Batteryless receiver at the
Canadian National Exposition. Rogers was
25 years old.
From 1925 until 1927, the only batteryless
radio receivers on the market—
anywhere—came from the Rogers plants.
After that, U.S. manufacturers caught up,
and the race was on to build and sell
millions and millions of receivers, just in
time for the Great Depression and what
came to be regarded as the Golden Age
of Radio. Rogers’ innovations, together
with the rural electrification campaigns
in North America at the time, suddenly
made radio listening affordable for cashstrapped
depression-era families everywhere.
By this time Rogers had moved on to
new things, too. He had taken his tube
designs and applied them to radio broadcast
transmitters. By 1927 he was ready
to build his first broadcast station, which
was also the first broadcast station in the
world to run directly off the power lines.
(Prior art used mechanical motor-generators
to develop the high voltage and
high current DC needed for the plate and
filament supplies, which from this end
of the century sounds complicated and
awkward at best). The station signed on
February 10, 1927, with 1 kW of power.
The call letters: CFRB (Canada’s First
Rogers Batteryless), Toronto. (It didn’t remain
at 1 kW for long.)
Rogers went on to design other specialized
tube types, and got the first TV
broadcast license in Canada in 1931. He
was involved in high frequency research,
and early radar experiments. But sadly, by
May 1939, it was all over—Ted Rogers,
Sr, dead at the age of 39.
46 BROADCAST DIALOGUE

ENGINEERING
Further reflections on multipath
BY DAN ROACH
First, a couple of additional comments
from those “in the know”
about multipath and CP. As I anticipated,
technical people far and wide have
strong opinions about whether to use
circular or horizontal polarization for FM
transmission.
Bob Calder of Victoria mentions an
instance where he can see a CP FM transmitting
antenna, and still can’t get decent
stereo reception from it because of excessive
multipath. In this case, the transmitting
antenna is fairly high gain, and quite
high up, so it’s quite likely that his reception
point is somewhat below the main
lobe of the transmit antenna. Since the
gain is so high, it’s quite likely that reflections
from objects in line with the main
beam are unusually strong.
The fact that the signal is CP is perhaps
adding to the problem, by providing
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additional reflections. (Back to my old
saw about the ratio of incident to reflected
signals). Bob mentions A/B tests he’s been
part of where HP has been demonstrably
superior (in relatively hilly terrain).
I also had an interesting discussion
with Dave Newberry of CBC Vancouver.
Dave mentioned an instance on the
Prairies where a change in facilities from
CP to HP has resulted in reception complaints.
His information raises the possibility
that I might have to modify my
(oft-repeated) statement about car radios
not being able to differentiate between
HP and VP signals.
Dave’s theory is that car radios are
usually getting sufficient signal from HP
signals because there are lots of reflections
around. The reflections randomize
the transmitted polarization sufficiently
to provide VP for the receive antenna. In
a flat prairie location, with fewer sources
of reflections, the car radio reception of
an HP signal seems to be impaired compared
to a CP signal.
Of course, if this is true, the fact that
a car radio is getting mostly reflected signals
from an HP source would lead one
to expect that the multiple reflections
would show more multipath problems
than a single incident signal from a CP
or a VP source. We would expect that car
radio reception of HP signals would be
somewhat better in mountainous terrain
than in flat terrain, but that there would
be more apparent multipath around that
hilly terrain than from a CP source.
I can’t say that I have seen, or rather
heard, this expected byproduct of Dave’s
theory. But still, it’s food for thought.
The main lesson I’ve learned over the
years from listening to FM and to learned
transmitter folk, is that when it comes to
FM propagation, there’s a lot of folklore
and anecdotal information, and very little
printed word or official documentation.
The little you can find in textbooks
must be considered critically. You’ll read,
for instance, in many texts that FM propagation
is not affected by seasonal variations.
Try and tell that to listeners in
the B.C. Okanagan, where multipath is
known to come and go in many regions
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
with the change of the seasons. Is this
due to changes in vegetation, or in the
moisture content of trees? The Okanagan
isn’t exactly known for either abundant
vegetation or moisture (on hillsides outside
of irrigation zones at least), regardless
of the season. But the phenomenon exists.
Another “textbook” fact is that skywave,
skip propagation and “ducting”
don’t occur at FM frequencies. Yet we read
every year about all kinds of intermittent
co-channel interference along the U.S.
Atlantic seaboard and the Caribbean,
with distant stations’ signals suddenly
appearing hundreds, sometimes thousands,
of kilometres from where they
belong, and interfering with local FM
radio. They disappear just as suddenly.
The new computerized FM measurement
sets from Audemat, that can make
thousands of comparative measurements
between several stations as they are moved
around in the coverage area, forming a
database with a connected GPS receiver,
may be able to shed some light on these
mysteries in the years to come. And yet, I
suspect that there will be just as many
new questions…
Next month, a story of cutting-edge
technical innovation that gave Canada’s
biggest radio station its call letters!
46 BROADCAST DIALOGUE

ENGINEERING
The story of Conelrad
BY DAN ROACH
Dan Roach
works at
S.W. Davis
Broadcast
Technical
Services Ltd.,
a contract
engineering
firm based in
Vancouver. He
may be
reached by
e-mail at dan@
broadcasttechnical.com.
This month’s article is concerned with
Conelrad (Control of Electromagnetic
Radiation), a broadcast system
that was put in place at the height of the
cold war to protect the U.S. in the event
of an air attack against North America.
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It’s a cautionary tale, and not without
its humorous moments.
In the aftermath of the Pearl Harbor
attack, the oft-told tale of Japanese aircraft
homing in on Oahu by using radio direction-finding
(RDF) on Hawaiian broadcast
signals must have preyed on defence
planners’ minds. That’s the only excuse I
can conjure up for what ensued with the
ill-fated Conelrad project.
In today’s world, where a couple of
hundred bucks will buy you a handheld
GPS receiver that can locate your position
in three dimensions almost anywhere
on the planet to an accuracy of a
few yards, it’s hard to believe that RDF
could ever have been such a threat.
Before Pearl Harbor, the U.S. Air Force
used to pay local broadcasters to stay onair
overnight to help guide in flights from
the mainland. It’s not too surprising that
the Japanese were able to turn the relatively
simple RDF technology to their
advantage. And any subsequent defence
plan had to take this simple technique
into account.
The problem was that broadcast signals
were essential to inform the public
of impending air attack. So some enterprising
types tried to figure out how to
keep broadcasters on the air, but make
their signals untraceable. Hence, Conelrad
was born.
In the event that enemy bombers were
approaching, regular broadcasters would
direct the public to a local emergency frequency,
then most would sign off. There
were originally two such frequencies, then
a third emergency frequency was added
to the AM band. Older radios show the
triangular civil defence logo on their
tuners at these locations.
Several transmitter sites in a given area
would switch to the same frequency and
would transmit simultaneously, carrying
the same emergency programming information.
Although there would be tremendous
co-channel interference between the
various transmitters, their signals were
judged to be “intelligible” most of the
time. The sound would be unpleasant, but
the essential message would get through.
And RDF efforts would be stymied by the
beats between the various transmitters.
The free world could be saved for future
generations!
Except that it didn’t work.
Fine in theory, it fell down in actual
practice. Field trials were attempted in the
New York area, with an RDF-equipped
bomber approaching at 15,000 feet from
about a 100 mile range. From far out,
there was no problem with the RDF
technique as all the stations in the test
were in the same general direction. As the
plane approached, the anticipated confusion
of the RDF equipment did not occur,
and the bomber successfully homed
in on and overflew WRCA’s transmitter
site. Bombs away!
Time to rethink the project.
It was then decided that some of the
co-frequency stations would transmit intermittently,
on for four minutes, off for
two, on for five, off for 2.5, etc. This was
tried, unsuccessfully: the station’s on and
off cycles became predictable, and accurate
time at each location to coordinate
the overall effort properly was a problem.
So, remote control circuits were installed,
with a central control point
turning the transmitters on and off in
a pseudo-random manner. Transmitter
plants needed to be modified extensively,
to operate on emergency frequencies, even
at reduced power. Transmitter technicians
needed to be on-hand at the sites to do
the retuning and adjusting required during
the tests or the emergencies.
Luckily, the system was never actually
used, because there was essentially zero
chance that it would ever have worked as
hoped. It was later dismantled in favour
of the EBS system, which recently was replaced
in the U.S. by the revamped EAS
system and Amber Alert.
In Canada, we simply had to rebroadcast
CBC or get off the air to give CBC
free reign.
Today, the only vestiges of the onceubiquitous
Conelrad program are those
triangles on the tuners of old radios, and
the Conelrad switch on old RCA transmitters,
that switched in that third, odd
oscillator (that no-one in this country ever
did have a crystal for!).
46 BROADCAST DIALOGUE

ENGINEERING
Depolarizing a polarized world
BY DAN ROACH
Dan Roach works at
S.W. Davis Broadcast
Technical Services Ltd.,
a contract engineering
firm based in Vancouver.
He may be reached
by e-mail at dan@
broadcasttechnical.com.
When we start talking about circular
and horizontal polarization
for FM broadcast, a lot of
broadcast technicians’ hackles start to rise.
Everybody seems to have an opinion to
share, but there’s very little hard evidence
to support the various views.
It turns out that multipath, despite
being ubiquitous, is a very complicated
subject, and what works for you doesn’t
necessarily work for me—this is a variation
of the principle YMMV (your mileage
may vary), which is itself a subset of the
infamous Murphy’s Law.
One of the arguments in favour of
circular polarization is that you essentially
get a free license to double your
transmitter power. Another is that the vertical
component of the circular transmission
provides enhanced reception to
vertical receivers (such as motor vehicles).
I say that these two points are debatable
at best…
I mentioned last month that the key
to improving stereo reception quality inside
the service area isn’t necessarily a
power increase—what we really need to
do is increase the ratio of incident to reflected
waves at the receive point.
While there’s little hard data on multipath,
there are a few items that have
come to light:
1) When a circularly polarized signal is
reflected by irregular objects (hills,
trees, etc.), the polarization data is
lost. The reflected signal exhibits random
polarization.
2) Vertically polarized signals are reflected
more than horizontally polarized
signals. Trees in particular reflect more
vertical than horizontal. This is one
of the few facts regarding polarization
propagation that you’ll find in a
textbook!
3) Vertical motor vehicle antennas, contrary
to public opinion and common
sense, receive horizontally polarized
signals just as well as they receive vertical
signals. Marvin Crouch of Tennaplex
used to say that the asymmetrical
grounded body of the car or truck
caused pattern distortion so that the
vertical whip antenna could no longer
discriminate between vertical and horizontal.
I don’t know about all that,
but the first part seems to be true.
What can we conclude from all this?
Circular polarization is not the panacea
that we were told it would be. While
in many cases it provides reception equivalent
to horizontal polarization, there
are several cases, particularly where the
geography provides lots of undesired reflections,
where CP signals are seriously
degraded versus HP.
This is most likely because of the increase
in reflected signals caused by
points 1) and 2) above.
I hope you’ve been noticing that I’ve
been careful in this column—and in last
month’s—to refer to stereo performance
inside the primary service area. Where
that extra CP power is useful is at the
horizon, in extending coverage in the far
field. And when we’re dealing with mono
transmissions, it may be an overstatement
to say that “all reflections are good”, but
only just by a little. Again, the CP signal,
with its extra wattage and enhanced
reflections, can seriously extend the coverage
of a mono signal—and that goes
double when the terrain is mountainous.
Receiver manufacturers have not been
ignoring the multipath problem, either.
There’s both good and bad news.
The bad news is that more and more
receivers are using variations of blend.
Blend circuitry senses marginal reception
and surreptitiously fades the receiver to
mono mode. While it does overcome
some of the noise and distortion of multipath,
an aggressive blend circuit can
mean that your station is received in
mono more than in stereo. Blend circuits
invariably work stealthily, because if they
blinked the stereo pilot light consumers
would soon catch on to their nefarious
design and start to complain.
The good news is the promise of digital
signal processing in receivers. Remember
last month when I was bemoaning
the fact that listeners wouldn’t stand
for lugging directional antennas around?
Some of the new Motorola Symphony©
designs manipulate phase and gain from
diversity antennas, in effect to produce a
multipath-minimizing directional antenna.
Controlled by the microcomputer,
these receivers constantly adjust the IF and
baseband signals for minimum distortion.
We keep hearing that the market will
be flooded with these DSP-based receivers
in the next few months, because in large
quantities they’re cheaper to produce than
old-fashioned analog sets. Bring ’em on!
46 BROADCAST DIALOGUE

ENGINEERING
The marginal path:
FM radio and the real world
BY DAN ROACH
was never meant to
be a mobile service. From
FMradio
the start, it was intended to
be a high-fidelity (monaural) medium for
listening in the home.
That’s one reason why FM coverage is
predicted, and measured officially, based
on using a horizontally-polarized antenna
10 metres above the ground: that’s about
the height of your average home rooftop
mast-mounted antenna (or at least it was,
back when people used such things). And
that of course is why all FM transmissions
were originally horizontally polarized.
That was the best way to get to
those horizontal rooftop antennas that
everyone had.
Of course, car radio development continued
to the point where a compact car
radio using a vertical whip antenna eventually
was able to pick up those FM stations,
too. FM transmissions upgraded to
stereo. And somewhere along the way,
some smart apples starting designing circularly-polarized
(CP) transmitting antennas.
These are able to transmit both
vertically- and horizontally-polarized
waves, and not just willy-nilly mind you,
but orthogonally to one another. As the
vertical wave reaches a maximum, the
horizontal is minimum, and vice versa.
To picture the plane wave sum travelling
through space is to visualize it spinning
in a circle as it goes: one rotation per
wavelength, hence the name CP.
Well, circular polarized waves have
some interesting properties. Aside from
being equally well received by either a
vertical or a horizontal antenna, when a
CP wave is reflected by an object, its direction
of rotation is reversed. This makes it
possible to discriminate between incident
and reflected signals, a useful property
that has never been fully utilized for
reducing multipath for FM reception
(you’d need to use a CP receive antenna,
and these have never been made for consumer
use).
Even so, CP allows full power transmission
to both vertical (car antenna)
and horizontal (home rooftop antenna)
receivers. Even more, CP seems to offer
something for nothing, especially the way
that effective radiated power is calculated
by Industry Canada and the FCC. These
august bodies take the greater of horizontal
or vertical radiation and ignore the
other plane, so that you can effectively
double the amount of RF that you transmit
for a given power level by using CP.
And more RF is good … right?
Well, maybe not—and certainly not
always. One of the biggest challenges for
quality FM reception is the presence of
multipath: phase cancellation of an FM
wave when out-of-phase signals partially
cancel out at a receive point. Generally
speaking, if there is an incident wave available,
it will be so much stronger than any
reflections that these may be ignored.
But when there is no direct path, multiple
reflections, travelling different dis-
tances to the receive point, may largely
cancel one another out. The effect is that
of a high-Q comb filter, cancelling some
frequencies and enhancing others. It is
much more critical for stereo than it is
for monaural transmissions. The result is
distortion and a “picket-fencing” effect,
even more pronounced with mobile
reception.
I said “generally speaking,” in the previous
paragraph. Of course, we’re dealing
with a statistical kind of thing here,
and there will still be locations, even
where an incident signal is available, that
the reflections will overwhelm it. The
key to improving reception quality inside
the service area isn’t a power increase—
we need to increase the ratio of incident
to reflected waves at the receive point.
How can we do this? We don’t have
much control over the path from transmitter
to receiver, except to choose a
transmitter site that offers the most best
paths for the most receivers (the grammar
is terrible, but you get the gist). If we
could just convince listeners to lug around
directional receive antennas and continuously
adjust them for minimum multipath,
that would help, but let’s get real
for a moment … we can’t do that either.
If they’d mount their antennas 10 metres
or so above ground, that would help, too,
but it doesn’t seem likely to happen anytime
soon. These suggestions are right
up there with CP receive antennas, and
diversity receivers … promising from a
technical point of view, but unrealistic
from a practical viewpoint.
Next month, all (or at least that small
subset of “all” that exists inside my skull)
will be revealed!
Controversy! Suspense! Pathos! Next
month in Broadcast Dialogue!
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
46 BROADCAST DIALOGUE

ENGINEERING
Look up in the sky! It's a bird!
It's a plane! It's a yagi!
BY DAN ROACH
Dan Roach works at
S.W. Davis Broadcast
Technical Services Ltd.,
a contract engineering
firm based in Vancouver.
He may be reached
by e-mail at dan@
broadcasttechnical.com.
We were discussing yagi and log
periodic antennas and their related
brethren, and the fact that
those antennas we refer to as “yagis” often
are something else, entirely.
Both these yagi and log periodic antennas
are frequently stacked vertically
and/or horizontally, to make up dual and
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quad arrays. An array may be used to increase
the gain of the antenna even further,
or to further tailor the directional
pattern of the basic antenna. When antennas
are stacked, the physical space between
the units is critical, as is the length of the
harness cables used between the antennas
and RF splitters/combiners.
The quad array pretty much represents
the maximum practical gain available from
a given antenna. Theoretically, in order
to realize a 3dB gain over a quad array
we would need to go to eight antennas.
In the real world, the additional cable
harness, connector and combiner losses
eat pretty badly into even that gain figure.
So we’ve reached the point of diminishing
returns.
It’s also common when using these
antennas for transmitting purposes to use
arrays of “skewed yagis” (antennas pointing
in different directions) to produce
many weird and wonderful directional
patterns. In this case, the power dividers
used can also be arranged to produce unequal
power divisions, to even further
enhance the number of choices available.
Most of the time, these antennas are
oriented for horizontal polarization, although
they may be used for vertical
polarization as well. An additional consideration
when mounting them for
vertical polarization is that the antenna
should then be located several wavelengths
above ground in order to function as
specified. Otherwise ground effects can
affect the impedance as well as the directional
pattern and front-to-back ratio of
a vertical yagi or log periodic antenna.
Yagis can be used in creative ways to
eliminate co-channel interference. One
technique is to mount two yagis, both
oriented in the same direction but staggered
in such a way that the incident
desired signal arrives at the first antenna
one-quarter wavelength before it reaches
the second antenna. A special harness is
constructed such that an additional
quarter-wavelength delay is encountered
by the feed from the first antenna before
it’s combined with the output of the second
antenna. Net result: incident signals
on the main lobe of the antennas are
delayed equal amounts, and sum normally.
Signals coming in from the back
of the antennas end up opposite in phase
and cancel out at the summing point.
The front-to-back ratio of the antennas is
increased significantly (at one frequency
of interest).
A more general technique to reduce
co-channel interference from a specific
known direction involves using trigonometry
and the known velocity of wave travel
to calculate the phase delay between two
antenna positions as seen from the source
of interference. This distance is adjusted
until the undesired signal arrives at the
two antennas 0.5, 1.5 or 2.5 wavelengths
apart. Summing the antenna outputs
causes phase cancellation of the undesired
signal, in effect placing a deep asymmetrical
null in the array’s directional pattern
at that frequency—in the direction of
the interference. Reception of the desired
signal is relatively unaffected.
It is even possible to make up a circularly
polarized array by coupling a horizontal
and vertical antenna through a
phase delay harness. The real benefits of
circularly polarized FM transmissions
have never been fully realized: a CP FM
receive antenna has a powerful mechanism
to reject multipath reflections (in
addition to directivity, that is), since reflected
circularly polarized signals “spin”
in the opposite direction as the incident
signal. This would be an advantage for
receiving fringe CP FM transmissions at
a rebroadcast site or cable company
headend, for instance.
However, the sheer physical size of
such a contraption would pretty much
prevent its acceptance on FM frequencies
by consumers.
Coming up next, we’ll stir the pot a bit
in a discussion of circular and horizontal
polarization for FM broadcast stations.
52 BROADCAST DIALOGUE

ENGINEERING
Yagi, Yada Yada Yada
BY DAN ROACH
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be reached
by e-mail at dan@broadcasttechnical.com.
It has become common usage in broadcast
engineering circles to refer to any
antenna that resembles a TV-type receive
antenna as a “yagi.” As in “did you
aim the yagi back to the studio?”
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It’s easy to see why this has happened:
“yagi” is a nice short word, and it doesn’t
sound like anything else I can think of
right now. But often enough, the antenna
we’re referring to isn’t even a real yagi at
all! Read on…
Strictly speaking, a yagi is an antenna
described by a pair of Japanese university
professors in the late 1920s. S. Uda invented
the antenna, but it was first described
in English by his colleague, H.
Yagi. It was the wish of both Messrs. Yagi
and Uda that their inventions be called
“Yagi-Uda” antennas, but the “yagi”
moniker is now so entrenched that it’s
here to stay.
The yagi antenna consists of a driven
element, which is typically a half-wave
or a folded dipole, and a reflector and
one or more directors. The reflector is
slightly longer than 1/2 lambda (one
wavelength is one lambda), and the directors
are slightly less. These parasitic elements
are critically spaced a small distance
apart—usually between 1/10 and 1/3
lambda—from the driven element. The
spacing and the number of directors help
determine the antenna’s characteristic
gain, input impedance, front-to-back ratio,
the magnitude of minor lobes, and the
antenna’s bandwidth. Typically the more
elements, the more gain. A six-element
yagi may have a gain of 10 dBd or so.
These antennas offer a compact solution
for VHF and UHF transmitters and
receivers—they are compact and have
significant gain. They have a high frontto-back
ratio, so can be used to reject
undesired reflected signals. They can be
easily aimed. But they are inherently narrow
in bandwidth, three percent or so of
the operating frequency, and this can
sometimes become a problem. It means
an antenna can be effective for, say, the
450-455 MHz link band, or a single TV
channel, but not for multiple TV channels.
The narrow bandwidth also makes
the yagi antenna’s performance suffer
under even mild icing conditions.
Well, there are always different antennas
for different needs. The yagi is very
attractive on many fronts, but the bandwidth
problem in particular was vexing.
Many variations of the basic yagi have
appeared as a result. Sometimes the parasitic
elements are detuned slightly to
“broadband” the antenna. Sometimes a
second driven element, tuned for a second
frequency, is added. Invariably, the
gain of the antenna suffers horribly, but
that may be acceptable in order to get
the improved bandwidth that is wanted.
The trick is to bend and twist the antenna
slightly so that the characteristics are fairly
even across the band of frequencies of
interest.
As a result, we see “modified” yagis on
the market that can, for instance, cover
more than one TV channel effectively.
Still, there’s sometimes a need for
even wider bandwidth in a directional
antenna. For instance, a cable television
company will often want to receive all
the VHF channels using a single antenna
or array at its headend. The solution here
is a whole different class of antennas
called “log periodics”. The log periodic
antenna can be designed to cover several
decades of bandwidth. The gain suffers
considerably compared to a yagi, but the
front-to-back ratio can still be quite
good, so that non-incident signals can
be rejected by this antenna, too.
A log periodic antenna can be recognized
by the fact that the parasitic elements
vary in length more than with a
yagi. This antenna looks like the profile
of a Christmas tree, with a triangular silhouette.
The formerly common VHF TV
masthead receive antenna (common
before the age of cable television, that is)
is usually a form of log periodic antenna.
Whether a yagi or a log periodic antenna,
the pointy end of the assembly indicates
the direction of maximum gain.
Another variant that has become quite
popular for rural TV reception is a log
periodic antenna with some yagi elements
added for UHF reception. The log periodic
elements can produce a nice smooth
pattern over the span of VHF and FM frequencies,
and the additional yagi elements
increase the gain at UHF frequencies,
where that extra gain is often needed.
More on yagis, log periodics, and their
relatives in our next installment.
46 BROADCAST DIALOGUE

ENGINEERING
Fighting the urge to surge
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at
S.W. Davis Broadcast
Technical Services Ltd.,
a contract engineering
firm based in Vancouver.
He may be reached by
e-mail at dan@
broadcasttechnical.com.
We were discussing lightning suppression
last time, and that just
seems to lead logically to surge
suppression techniques in electronic
equipment. It’s a huge industry, and the
continuing popularity of fragile computer
equipment means it’s getting bigger all
the time.
There’s a lot of black art and pseudoscience
involved, too.
The surge we’re trying to protect our
precious equipment from is an abovenormal
voltage. For the time being we
don’t need to worry about where it came
from: maybe a direct lightning strike,
more likely an inductively- or capacitivelyinduced
spike, or a wallop from switching
action on the grid (are you listening,
Ontario Hydro?).
The basic building block of all surge
suppression is the transient suppressor.
There are two basic flavours: some devices
change their impedance exponentially as
voltage is raised, others have a threshold
voltage where they suddenly change behaviour.
Your thyrites and MOVs (metaloxide
varistors) are in the first category;
gas discharge tubes and zener diodes are
in the second.
A thyrite is usually a stack of disks of
silicon carbide, often in a high-voltage
power supply. They’ve been around since
the 1930s, originally for protecting highvoltage
transmission lines. They drop in
resistance when the voltage is raised. They
can handle large amounts of power, but
you don’t see them much in today’s
designs—one of the reasons being that
they draw a significant amount of current
even under normal voltage conditions.
So they’re quite big, and can get
quite warm. But they were one of the earliest
forms of suppression, and they led
to the MOV.
MOVs are ubiquitous today. They’re
mostly made of zinc oxide, with a few
trace elements thrown in. They have a
much sharper “knee” and leap into action
more sharply than thyrites. They’re cheap
and reliable and can handle a fair amount
of energy, and when they fail they shortcircuit.
That can be a good thing, since
they’ll continue to provide circuit protection
even after they’re cooked. Unless
they explode.
Which they do, quite often.
MOVs have gotten a bit of a bad reputation
(apparently unearned) amongst
the so-called experts, though. There have
been claims that they are slow to react,
and that their voltage threshold (the location
of the “knee”) drifts after they’ve
been used. Further research has shown
that the basic electrochemical process in
the MOV takes place in about 500 picoseconds
(that’s pretty fast!) The culprit in
the slowdown, of course, is the inductance
of the component leads, and we can
minimize that by using good RF techniques
and keeping leads as short and
direct as possible. And it turns out that
the threshold does change with use, but
as the component ages (after a few more
“hits”) it returns to its nominal value.
Gas-discharge tubes are used in telecom
circles, along with carbon contacts
(“carbons”). They consist of a couple of
closely-spaced contacts in a metal tube.
Not much call for them in power supplies,
since once they start arcing, they won’t
stop until the voltage is near zero. Good
potential crowbar, though. Some small
transmitters (Telefunken is one) place
them across the output terminals.
Zener diodes can make an effective
crowbar, too, but they are somewhat frail.
Over-voltage conditions create a very
small active hot spot inside them, and
this is where they tend to fail. When they
fail they may go short, or open, or somewhere
in between. Some manufacturers
claim zener action can take place in one
or two picoseconds, which may be true
at the molecular level but defies belief
for any leaded component (read: in the
real world).
Which is why 99 times out of 100
you’ll find the MOV doing the job.
In addition to the transient suppressor,
which is placed as a shunt to take the
surge away from the load, many devices
include a series low-pass filter to delay the
surge’s passage to the load, and give the
suppressor time to work. Sometimes a current-limiting
device (a resistor or fuse, perhaps)
is placed in series with either the
shunt or the load to prevent its destruction.
RESULT OF LAST MONTH’S QUIZ:
Here’s a circuit
to convert a
dual linear potentiometer
into a single logarithmic or almostaudio-taper
pot. Hey, it might come in
handy some day!
46 BROADCAST DIALOGUE

ENGINEERING
Lightning, grounds and
other accidents of nature
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract
engineering firm based in Vancouver. He
may be reached by e-mail at dan@
broadcasttechnical.com.
Over the years, the question of
what constituted a good technical
grounding has been answered
in very different ways. Still, just about anyone
would concede that an AM transmitter
site has about the best ground system
there is, with its thousands of feet of
buried ground radials. Couple that excellent
ground with one or more great big
lightning rods (that’d be “towers” to you)
pointing skyward, and you have the classic
elements for nature’s electrical fireworks.
The classic modern paper on lightning
abatement (perhaps “redirection”
is a better word) was written years ago
by Nautel (it’s called Lightning Protection
for Radio Transmitter Stations, ©1985
NAUTEL), and is included in their transmitter
service manuals. When Larcan
wanted to cover this topic in their manuals,
they asked for and received permission
to reprint the Nautel stuff in their
books, too.
Both manufacturers are trying to
describe installation procedures that will
minimize damage to their products,
should nature come calling with a stroke
or two of enlightenment. There’s a lot of
good information there, but two facts that
have stuck in my mind, and that are capitalized
upon to reduce damage, are (a)
lightning has a very, very fast rise time;
and (b) coaxial transmission lines have
both a differential and a common mode,
just like twisted pair wires.
And there can be other applications
of this information, too.
Since a lightning pulse has a very sharp
rise time, its forward pulse acts as if it has
a very high frequency component. At last
we have some evidence that those lazy
loops placed in the base connection to a
series-fed AM tower actually do some
good—I remember when they were kind
of controversial, with some saying they
helped redirect lightning across the ball
gaps at the tower base, and others stating
that they did no good whatsoever. The
slight inductance caused by the loops
should look like a brick wall to the steep
lightning pulse looking for a quick way
to ground.
I confess that prior to reading that
paper, I never thought about differential
mode in coaxial lines. The shield was at
ground, and just “there”. The placing of
large ferrite toroids over top of the transmission
line seemed like heresy, and
makes you stop and think about differential
vs. common modes: after you’ve
reflected on it for a while, you realize
that to a common mode pulse, that
toroid represents a great big choke, but it
is invisible to a differential signal (like
the transmitter output).
Incidentally, those smaller snap-together
ferrites are available from Digi-key
and others (sometimes including Radio
Shack), and I’ve developed the habit of
carrying a couple in my toolbox—they’re
great problem solvers for RFI at transmitter
sites and elsewhere. I sure have been
seeing them used a lot by manufacturers
in newer computer and telecom equipment.
Quick and easy to use, they can be
surprisingly effective. They come in several
flavours: round, square, and there’s even
a rectangular version for ribbon cables.
The argument in their favour would be
that RFI tends to come into equipment
common-mode, same as the lightning in
the last paragraph. For really stubborn
problems, don’t forget that you can loop
your cables through the toroid more
than once…
Sneaky Trick of the Month:
Let’s say you’re in the field and have
a quick need for a logarithmic-taper
potentiometer, but all you can find in
your junk bin is a dual linear pot of the
right resistance. There’s a really simple
circuit to make up a log taper from it—
can you figure it out?
The solution, next time…
44 BROADCAST DIALOGUE

ENGINEERING
Practising transmitter safety
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Last month I regaled you with true
horror stories about accidents at the
transmitter site. This month let’s try
out a few ideas that would prevent these
mishaps.
Have you ever noticed when you have
tower riggers at the transmitter site, that
they’ll barely get out of their truck without
putting on their hard hats? These people
do this for a living, and they don’t
take safety for granted. Hard hats are available
practically everywhere, and they’re
very inexpensive. Get yourself one and
wear it whenever you’ve got people working
on the tower.
I shouldn’t have to mention that tower
work is a specialized job and should be
undertaken only by professionals in that
field. If the height and the hazards don’t
give you pause, the liabilities that your
employer incurs whenever you hop on a
“
You just
know that
whatever you
can contribute
to VoicePrint
is worthwhile,
recognized
”
voiceprint@nbrscanada.com
tower should prevent any attempt to do
tower work yourself.
We’ve all met technicians who think
nothing of running up a tower to relamp
it, usually without adequate safety equipment
or any knowledge of what they’re
doing. To repeat—the insurance issues
alone should prevent this from ever happening.
These people don’t belong in
our industry.
When you take an emergency field
call, especially after hours, make sure that
someone knows where you’re going and
how they can reach you before you dash
off into the wilderness. It’s also smart to
keep a few survival supplies handy in your
vehicle, too. A broken fan belt may be the
only thing between you and a disabled
vehicle on a deserted road in the middle
of nowhere in the middle of the night.
Of course, my main point last month
was that the primary risk to life that we
all face at transmitter sites is electrocution
from high voltage. If your transmitter
has a shorting stick, make ample use
of it before reaching inside. If there’s no
shorting stick, get a big screwdriver and
use it to short possible energized points
to ground.
While it would be very simple for me
to make the blanket statement that you
should never, ever operate a transmitter
with interlocks defeated and the doors
open, the fact remains that we’ve all found
it necessary to occasionally look inside a
transmitter while it’s operating. Sometimes
this is the only way to troubleshoot
a troublesome rig. But use extreme caution!
Think hard about any alternative,
safer procedures that you could try instead.
Often you can contrive another,
less exciting test that will give you the
information you need at less risk. Step
back and visualize what you’re planning
to do, and what could go wrong. Think
about it thoroughly. Then think about it
again! Take off wristwatches and rings.
Put one hand in your pocket. And don’t
go poking around in the transmitter
when the power’s connected! Limit your
adventure to observation only!
When dealing with gutters and mains
distribution panels, it’s entirely justifiable
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
to refuse even an inspection if the power
cannot be disconnected. Many thoughtful,
experienced technicians share this view.
On the other hand, you’ll find many
technicians who will not hesitate to
reach inside a live panel. Most of us fall
somewhere in between. My personal rule
is to treat this kind of situation similarly
to the transmitter example above—avoid
it if at all possible.
Think about what you plan to do, and
what could go wrong if things don’t turn
out as you expect. Think about it some
more. If I can’t contrive a way around it,
I might proceed—with extreme caution,
and only with someone around to observe
and intervene. Often having someone
around with whom you can discuss the
problem will prevent some of the sillier
stunts from even being attempted.
If it’s just a matter of getting some
out-of-service time to shut down the
panel, think seriously about that. If it’s
an emergency and needs doing now, then
maybe a short power interruption and
off-air time are necessary right now. At
least, make sure you have a hard hat and
safety goggles.
And if, after considering it slowly and
thoroughly you’re still scared thinking
about it, just don’t do it. Come back later
and do it safely!
54 BROADCAST DIALOGUE

ENGINEERING
Safety Code One or
diatribe about danger
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
We were chattering about Safety
Code Six a couple of columns
ago … and while it’s still fairly
new—and it’s of particular interest to
Industry Canada—today I want to talk
about something eminently more downto-earth.
No one has ever been demonstrably
harmed by electromagnetic radiation at a
broadcast site. Contact currents can burn
us, and we’ll likely remember it for quite
a while since healing from this is notoriously
slow. But you won’t die.
The greatest hazard to life that we face
in broadcast engineering is electrocution.
We deal with high voltages and currents
routinely, and very safely—there are not
a lot of casualties in our business. But
there are a few, and they rightly tend to
make news. Perhaps they’ll act as a deterrent
to future accidents…
Ohm’s Law Applied to a Short Circuit
You are alone at a transmitter site that
has a surge suppression system installed
at the main distribution gutter, i.e. after
the main hydro disconnect, but unable to
be de-energized on its own breaker or
cutoff switch. There are six status lights
on the front of the suppressor box, and
two of them are extinguished, indicating
that an internal fuse on one of the three
phases has blown.
You know that you should not replace
a fuse while the circuit is hot, and you
know that you should not work on this
by yourself. But no one else is around
right now, and to kill this circuit would
take the station off the air. You
know you really should
come back late at night,
and you would rather
not have to do that so
you figure you’ll just
be extra careful and
ensure that you do
not become part of
the circuit.
But what you do
not realize is that
the fuse blew in the
first place because the
MOVs inside the suppressor
module have failed
destructively by shorting.
When the fuse is replaced, the
replacement fuse instantly explodes in
your face causing second and third degree
burns to your face and your arms.
As you stumble, dazed, out of the
transmitter building into the open air,
the door slams shut behind you, locking
you outside with your keys inside. But
you are lucky to be alive.
An air conditioning technician was
killed in Vancouver earlier this year when
he powered up an HVAC unit that was
accidentally wired to short. He was not
electrocuted. The short caused the switch
panel to explode when he powered up.
Part of the panel blew off and struck his
head. He was not wearing a hard hat.
Ohm’s Law Applied to the Human Body
You are alone at the transmitter site.
You are having a pesky problem with the
power supply intermittently overloading.
In order to get a better look, you
defeat the interlocks and leave the back
door wide open while the transmitter is
operating. After a while, you get braver,
and start carefully poking around inside
the cabinet.
You wake up lying on the transmitter
building floor. You have no idea how you
got there, or how long you’ve been unconscious.
The transmitter is still happily
running, with the back door open.
Eventually, much later, you
notice small burns on your
back and one of your feet.
You, too, are lucky to be
alive.
Ohm’s Law Applied
to the Human Body,
Part II
You are a chief
engineer at a transmitter
site with your
assistant, and you have
a nasty transmitter
problem. You eventually
are able to solve it, but
many hours have passed, and
you are very weary. Now you’re
just cleaning up the transmitter to place
it back in service, and have finished dealing
with the high voltage circuits, so you
feel pretty safe.
Unfortunately for you, you’ve become
tired and careless, and although
you don’t contact the high voltage, you
do come in contact with 120 VAC. In
your weakened condition, your heart
stops. Your assistant is able to summon
help and apply artificial respiration until
help arrives, but you never completely
recover your faculties, and never are able
to work again.
These accidents all happened more or
less the way I have described them. And
they all happened to experienced technicians,
not newcomers to our trade.
Let’s continue this theme next month.
44 BROADCAST DIALOGUE

ENGINEERING
Perils of the dog biscuit
BY DAN ROACH
Last time we were noting how the
humble dB has been used, and
abused, and how it has spread like
a computer virus throughout engineering
circles. It’s now used to measure so many
things (other than audio power) in so
many ways (often incorrectly) that much
of its meaning can be lost.
Let me get back to basics before I confuse
anyone (including myself) any further.
It is possible to make sense of this
bedlam, by rigidly enforcing two simple
rules:
1. The decibel is always used to express a
ratio of power levels. Quantities that
are not powers must be made proportional
to power. Since power is proportional
to the square of voltage for
a fixed impedance, output and input
voltages may be squared before calculating
their ratio. Most people just
remember to multiply the log of the
linear quantities (e.g. Volts) by 20 instead
of 10, which can accomplish the
same thing in fewer steps, but you
must remember this only works if the
impedance remains the same throughout.
If the impedance changes, you
must work out the output and input
power some other way (like figuring
out the resistance at each point and
calculating the powers from there),
before logging and multiplying by 10.
2. The units used to measure the input
and output power levels must be the
same, so they will cancel out. Example
measurements could be in watts, volts,
cubits, or pints of beer. As a result
decibels themselves have no dimension
as such, and so technically
speaking they are not units. The dB
(without any suffix attached) is used to
measure power ratios, so it can measure
gain or loss, but there is no reference
to either the input or output
level, just the ratio. The statement “I
set the level to 0 dB” is meaningless”.
Make these two simple rules into
your dB religion, and you’ll find you
won’t have nearly as much trouble working
with decibels.
An additional note concerning dBs
and audio: because modern audio systems
don’t worry much about impedance
matching (all sources are very low
impedance, and all inputs are very high
impedance, so “open-circuit” conditions
prevail), there has been a transition from
using dB with power references (“dBm”)
towards voltage references (“dBu”).
A few months ago in this very space,
I was referring to older transmission
practices in broadcast, and used “dBu.”
Laverne Siemens of Golden West quite
properly pounced, and reminded me that
in the old days nobody used the expression
“dBu.” Transformer coupled audio
equipment would be specified using
dBm, since impedance was still vitally
important then. Today we use dBu (0
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
dBu = 0.775 V, the voltage across a 600
ohm load at 0 dBm) extensively, and
sometimes carelessly, and pretend that
impedance doesn’t matter. And it doesn’t,
really, as long as it doesn’t change. But
try always to remember the power origins
of the decibel, and you’ll avoid a lot of
confusion, and have guaranteed happy
karma.
dB = 10 log(PO/PI) = 10
log(VO/VI)2* = 20 log(VO/VI)*
(*but only if the impedance
remains the same!)
22 Commerce Park Drive
Unit C-1, Suite 255
Barrie, Ontario L4N 8W8
Tel: 705-487-5111
Fax: 705-487-2444
Email: info@ramsyscom.com
Web: www.ramsyscom.com
RAM
for
quality
prod-
TORPEY TIME
46 BROADCAST DIALOGUE

ENGINEERING
Many flavours of dog biscuits
BY DAN ROACH
Aren’t logarithms wonderful? Witness
the many confusing flavours of
the deciBel (dB, or “dog-biscuit,” as
my old friend Mike Fawcett—former technologist
extraordinary, now lost to engineering
and busy exploring the strange
world of broadcast management—so often
referred to them).
This story (like all my stories lately)
starts with the telephone company using
telegraph wires for transmission, and
needing a measurement to describe the
losses they were encountering. They
started using a unit called “miles of loss”,
which described the amount that a signal
would be attenuated by passing
through a #19 wire loop a mile long.
Later this expression was modified to
“transmission unit”, and still later someone,
thinking it would be nice to commemorate
Alexander Graham Bell, created
the Bel—the logarithm of the ratio of
output and input powers.
The Bel was pretty big though, like
measuring your personal weight in
tonnes, so they divided the Bel by 10 to
make the deciBel. Ten deciBels to the
Bel. A loss or gain in deciBels is 10 times
the logarithm of the ratio of output to
input power. So far so good. (By the way,
someone out there needs to know that
there’s 1.056 dB to one mile of loss, but
I digress.)
So we had a nice, although somewhat
unusual, unit to measure power ratios—
the deciBel. Unusual, because it’s logarithmic.
Specialized, because it’s intended
for measuring power ratios of audio on
telegraph lines. Relative, because it was
only defined for ratios, and so it was
ideal for stating the gain or loss of signal
power through amplifiers, filters, attenuators
and transmission lines.
It was right about then that all hell
broke loose. First of all, people started
using the dB to measure all kinds of stuff
other than audio power (I swear, if some
engineers had their way the Richter Scale
for measuring earthquakes would be calculated
in dB). Secondly, by tacking on
another letter, they came up with a number
of logarithmic measures of absolute
level of all kinds of stuff.
It started innocently enough, with the
dBm, a level of power related to one
milliWatt. 0 dBm = 1 milliWatt. Simple
and effective. But trouble was on the way.
It’s tough to measure power directly,
so most often our instruments are actually
voltmeters with a scale calibrated to
read off the power at a particular impedance.
Telephone guys stick to 600 ohms
most of the time, but RF folks prefer 50
or sometimes 75 ohms. And the voltage
across 0 dBm at 600 ohms (0.775 V) is
different at 50 ohms (0.224 V) or 75 ohms
(0.274 V). Uh-oh!
And the dB is such a neat little package,
why not let’s use it to measure ratios
of all kinds of stuff, not just power!
Double uh-oh!
What have we wrought! It’s logarithmic
bedlam! I’ve omitted some of the
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
more obsolete expressions, but there’s
still plenty in current usage left to go
around:
• 0 dB SPL = 20 uP (sound pressure) used
in mic specifications.
• 0 dBm = 1 mW (power, audio or RF)
• 0 dBu = 1 uV/m (RF field strength); or
• 0 dBu = 0.775 V (voltage, audio) using
the same symbol for extra confusion
• 0 dBk = 1 kW (power)
• 0 dBmV = 1 mV (voltage, RF) the cable
TV industry likes this one
• 0 dBuV = 1 uV (voltage, RF)
• 0 dBW = 1W (power, RF) Industry
Canada license applications
• 0 dBV = 1 V (voltage, audio)
• 0 dB PWL = 1 pW (power, acoustics)
• 0 dBrnc = -60 dBm (power related to
reference noise level, c-weighting)
telco audio
The trend is clear, so brace yourself
for the following, as the deciBel continues
to make its way into everyday usage.
Fuel costs will rise 1.5 dB this summer.
Computer capacity will continue to increase
6 dB per dollar every 18 months.
And the Canadian dollar will continue
to be worth about -1.25 dB USD (0 dB
USD = 1 U.S. dollar).
And you thought switching to metric
was a pain! Maybe it’s not too late to
switch back to “miles of loss!”
46 BROADCAST DIALOGUE

ENGINEERING
Eeek! It’s Safety Code Six!
BY DAN ROACH
Industry Canada used Canada Post to
drop a small bomb on AM stations
…a belated Christmas present, as it
were. Safety Code Six, enacted by Health
Canada a number of years ago to protect
the public from excessive levels of RF radiation,
has finally come home to roost at
AM transmitter sites.
For most of us, the main impact up
to now from Safety Code Six has been
more strict guidelines for our tower riggers
when tower work has been needed.
Now Industry Canada has informed us
that AM transmitter sites must be made
to comply with Safety Code Six right now,
which is a ironic since all AM transmitter
sites inherently break the Code to a certain
extent. Even a 1 kW transmitter site will
have areas near the tower(s) where one
can get overexposed, or come in contact
with currents exceeding the Code limits.
Fortunately, Industry Canada is looking
for some fairly practical matters for
compliance. The intent is to prevent the
general public from getting too large a
dose of radiation, or excessive contact current.
The first line of defence at an AM
site is the fencing around each of the towers
in the array. It should be at least two
metres tall and locked. There should be
red Danger signs around the towers—
more about that in a minute.
Since there are if not hot, then perhaps
warm areas near the towers, we’re now
required to place amber warning signs at
the site’s perimeter, which may be a new
concept for most of us. Very few AM
transmitter sites have perimeter signage
already in place, so this will be something
new. Part of the Safety Code Six
bulletin contains a description of the signage
necessary. An important comment
from Industry Canada adds that the signage
should be bilingual. CAB has come
up with some fine examples for your
local sign-maker. They must be at least
9" x 12" in size. Send me an e-mail if you
need a copy.
Transmitter Maintenance Tips Your Tx
Manufacturer Never Told You!
I have a small pet peeve with the
Nautel transmitter company. They seem
to hate to inform the transmitter-using
public (you and me) when there’s something
that needs saying about one of their
products. I’ve tried to tell them over and
over that we love to hear about these
things, especially if they help us to improve
their transmitter’s reliability. Maybe
one day this stuff will appear on their
Web site, but until then…
(A) Those who have been maintaining
Nautel AMPFET 50 and the ND series
of Nautel transmitters may already
know this, but those I canvassed did
not so I include the information here:
there is a tuning coil on the back of
each PA amplifier cube. The manual
tells you that you need only worry
about adjusting the coil if you change
the transmitter operating frequency.
The manual is incorrect! You may also
need to adjust the coil if you have
Dan Roach works
at S.W. Davis
Broadcast
Technical
Services Ltd., a
contract engineering
firm
based in
Vancouver. He
may be reached
by e-mail at
droach@direct.ca.
changed more than “a few” of the RF
power transistors, P/N IRF 140.
When International Rectifier upgraded
the IRF 140 transistor, they
tripled its gate capacitance. As you
change more and more transistors in
your transmitter with the new type,
the resulting detuning causes more
and more current to be drawn from
the exciter RF output. Eventually, the
transmitter will either shut down
from low RF drive, or blow the fuse
powering the RF amplifier inside the
exciter.
Nautel has a test jig available for
inserting in the feed to each cube,
which produces a sample voltage proportionate
to the current drawn by
the cube. The coil is then adjusted
for minimum sample voltage.
(B) Next time you are repairing a PA assembly
in an elderly Nautel transmitter,
check those three huge electrolytic
capacitors in the cube assembly. I have
been double-checking lately, and have
been surprised to find quite a number
of them have dried out and
opened up. They are the main filters
that regulate B- voltage for the transmitter,
and I imagine the transmitter
operates better when they’re doing
their job.
I don’t know why I was surprised
by this—how many electronic devices
do you know of that don’t require
their electrolytic capacitors to be replaced
after 10 or15 years? It just never
occurred to me…but make sure it
occurs to you.
46 BROADCAST DIALOGUE

ENGINEERING
The history of broadcast engineering:
Chapter CCCXLIV
BY DAN ROACH
Did you ever wonder how we arrived
at so many of the standards that
we use every day?
I don’t mean standards like the volt
and the ohm, which are covered in high
school electricity courses. I mean, for instance,
why do we use 19” racks? Answer:
the U.S. Navy developed the standard.
EIA hopped on board later, giving it a
sort of professional gloss. The U.S. Navy
was also responsible for specifying that
special grey colour that gets sprayed on
most things.
Of course, many of our standards come
from the phone company. They developed
the VU meter, for instance, and in typical
telco fashion specified it more or less to
death. Meters that do not fully comply
with the VU standard are more properly
called “VU-style” meters, or VIs (volume
indicators)—and there are many of these.
Part of the standard covers the ballistics
of the needle, which is a good thing…a
proper VU meter will not have significant
over- or under-shoot when exposed to a
300 mS 0 VU burst of 1 kHz tone.
But did you know that the only true
dial colour for a VU meter is “buff?”. By
the rules, a white-faced VU meter doesn’t
fully comply with the standard, and so is
not a true VU meter! No doubt the telco
types researched and found that “buff”
was particularly pleasing to the eye!
In the old days, transmission standard
level was +10 dBu, and studio equipment
was typically set for 0 VU = +8 dBu. Ever
wonder why most modern equipment is
set up for 0 VU = +4 dBu? Well, it has to
do with the output driving capabilities of
early generation integrated circuits. The
+/- 15V supply rails that ICs operated on
would allow an output level of +14 dBu
before clipping, but not +18 dBu. Since
they couldn’t get the necessary 10 dB headroom
over standard operating level, they
dropped the operating level to +4 dBu.
Later generation IC’s that were meant for
use in pro audio gear were able to run the
rails up to +/- 18V, which solved this problem,
but the die had already been cast.
At least one transmitter manufacturer
in the 1970’s (CCA) decided to make the
input level of their transmitters 0 dBm
instead of everybody else’s +10, reasoning
that most station engineers of the day
were using Heathkit test oscillators, which
couldn’t make it to +10 dBm.
Our standards of “tip” and “ring”, the
phone plug, and many of our multipair
cable colour codes, come from the telephone
company (or sometimes from
Belden). The ubiquitous BNC comes from
the U.S. Navy (“Bayonet Navy Connector”),
as do its siblings, the TNC (“Twist
Navy Connector”), and the N (go ahead
and guess) connector.
Need to implement DESCRIP-
Your MSC Regional Sales Manager
has cost-effective solutions.
wrice@msc.ca • tambrose@msc.ca • jdesmarais@msc.ca
products, design, installation and service at
www.msc.ca
The West: 800-663-0842 • Ontario: 800-268-6851 • Quebec: 800-361-0768 • Maritimes: 800-268-6851
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
XLR connectors came originally from
Cannon, and there’s a long and storied
history there. The XLR we know today is
the “miniature” version of the original big
beast, which frankly was more suitable for
hooking power up to welding machines
than carrying microphone audio.
A grand battle over phase polarity (is
pin 2 + or -?) was fought for many years
between Ampex and Studer, with the
Swiss triumphant finally. That one forced
some of us to reverse the habits of many
years (and look what it did to Ampex!).
The designation “B+” to refer to the
main power supply lead of an amplifier
goes back to the early days of radio. “A”
referred to the filament supply, “B” to
the plate, “C” to the bias, and “D” to the
screen grid supply. This even carried over
to the naming of the older battery types,
with the “B” cell being rated at 67.5 V for
the plate supplies of radios (and when we
last checked, B cells were still available
from Eveready!). It took the Canadian
Rogers Majestic company to change the
landscape with the Rogers Batteryless
radio, for which CFRB is named.
But that’s another story, for another
day…
46 BROADCAST DIALOGUE

ENGINEERING
The wisdom of the ages!
BY DAN ROACH
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd.,
a contract
engineering
firm based in
Vancouver. He
may be reached
by e-mail at
droach@
direct.ca.
Now it all becomes clear… Or, at
least to those of us on the consuming
end of broadcast equipment,
it seems that way.
A belated tip of the hat to the late
Mel Crosby of Pineway Electronics, who
delivered this into my hands many years
ago, and in the process cleared up many
a mystery!
“
I’m thankful
that
VoicePrint
exists and
has given volunteers
this
wonderful
opportunity
to
be of service
”
voiceprint@nbrscanada.com
A Guide to Interpreting Specs
Manufacturers have now developed a special language to proclaim the many virtues
of their fine products. Sometimes, these virtues cannot be completely understood
by the normal person until they have the anointed translation in their hands. So,
here is your guide to the wisdom of the ages!
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ACROSS THE COUNTRY
Different colour from previous design.
Parts not interchangeable with other designs.
Imported product.
Almost as good as the competition.
Costs cut to the bone. (Manufacturer’s costs).
No provision for any adjustments at all.
The advertising agency doesn’t understand it.
Rush job; nobody knew it was coming!
Manufacturer lacks good test equipment.
Unit on which all parts fit.
Factory had a big argument with distributors.
We finally got one that works.
Nothing we had before ever worked
THIS way.
We finally figured out a way to sell it, and
make even more profit.
No other reason why it looks the way it does.
A different shape and colour from the others.
Impossible to fix.
Previous faults are corrected, we hope.
Assembly machines operated without
gloves on.
Will operate through the warranty period.
Ours, not yours!
Manufacturer’s, upon cashing your cheque.
Does things we can’t explain.
Heavy as hell!
Gives a picture and produces noise.
One of our techs was recently laid off
from Boeing.
We made it work long enough to ship it.
Feels so smooth!
When completed, it will be shipped by
Greyhound.
Finally got all of it to fit together.
Our old design didn’t work; this one
should get us out of trouble.
Got a deal at the Government surplus auction.
Within 24 hours, we can usually find a
second person to ignore your problems.
You can return it to us from most airports.
46 BROADCAST DIALOGUE

ENGINEERING
Further adventures with Ma Bell
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
This month I propose to finish off
my diatribe from last time, about
the importance of proper source
impedance when driving telephone lines,
with a roundup of information about
analog lease circuits.
I was describing an electrically long
(i.e., >300 m) twisted pair, in terms of its
series inductance and resistance and shunt
capacitance, as being similar to an analog
low-pass filter. The equivalent circuit
is shown in Figure 1A. I was attempting
to show how the response at the output
of the line varied with R, the impedance
of the audio source. Why is that?
Well, it’s because it varies the Q of the
series RLC circuit, of course, as we know
from our AC theory. In Figure 1B you can
see how the upper frequency response
varies with R. As the source impedance is
reduced, the Q of the filter is increased,
and the attenuation of high frequencies
is delayed until the inevitable plunge to
zero output at infinite frequency.
The traditional approach to flattening
the response is to equalize it with a parallel
resonant RLC circuit, arranged as in
Figure 2A. If you look carefully, the bottom
half of the response curve (below
resonance frequency) complements the
response curve of the uncorrected telephone
line—add ‘em together and you
should get unity!
By adjusting the resonance frequency
of the equalizer to just above the frequency
response desired, and varying the
damping resistor to adjust the loaded Q,
one can get a fairly flat resultant response
from the program circuit. With this type
of equalizer, frequency response above
resonance drops like a rock, reducing
out-of-band noise as an added benefit.
But since the equalizer is completely passive,
it can’t boost frequencies that have
been lost in the line, it can only attenuate
frequencies that have less loss to balance
the response.
A long line can have a lot of inherent
high frequency loss so that at the output
of one of these equalizers, levels will need
amplifying, sometimes a lot! Which is
why we’ve progressed from the simple
RLC equalizer shown, to more modern
equalizers from folks like Tellabs and
McCurdy Telecom that can provide gain,
and other features like phase equalization.
Because, you see, these old RLC circuits
can kind of ruin the phase response
of a line. This subjectively doesn’t sound
too bad with a moderately-equalized cir-
cuit, but can show up as an odd kind of
hollow sound when extreme amounts of
equalization have been used.
At least we’ve chosen an unloaded
pair. Normally, telcos add loading coils
every fraction of a mile, which add series
inductance, with the net effect that line
attenuation is much reduced in the
voice-band (300-3kHz), but drops precipitously
above that. Once the audio’s
been through this kind of mess, it’s
impossible to smooth out to get better
high-end response. Instead of a smooth
attenuation curve, you end up with
bumpy in-band response followed by a
sharp drop-off.
One trick that old-timers have been
known to use can come in handy when
you have a fairly short loop and no budget
for equalizing: you can use a pair of
repeat coils to drop the impedance of the
source from 600 to 150 ohms, which
more closely matches the actual impedance
of the line. At the receive end, you
pop in another repeat coil to get from 150
back up to 600 ohms. The circuits need
to be properly terminated with 600 ohms
at each end. The result is flatter response
and less attenuation than if you had left
the circuit at 600 ohms throughout.
Dan Roach works
at S.W. Davis
Broadcast Technical
Services Ltd., a
contract engineering
firm based in
Vancouver. He may
be reached by
e-mail at droach@
direct.ca.
46 BROADCAST DIALOGUE

ENGINEERING
Resistance is futile – but
impedance is (sometimes) important
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach
works at S.W.
Davis Broadcast
Technical
Services Ltd.,
a contract
engineering
firm based in
Vancouver. He
may be reached
by e-mail at
droach@
direct.ca.
In the old days, audio equipment manufacturers
paid a great deal of attention
to the input and output impedances
of their products. Modern op-amp circuit
design has made a mockery of the lengths
to which these manufacturers went. Try
looking at a schematic for an old CBS
Audimax, with input and output level
controls made up of three-section potentiometers
configured as “T”–pads. Or for
real humour, try any of the old Ampex
tape machine audio circuit designs…
The reason for all this attention to
detail was obvious at the time—unless
balanced lines were sourced and terminated
at the proper impedance, “bad”
things would happen. We were all taught
to just terminate everything properly, and
life would be good. The real smart guys,
we knew, could sometimes make miracles
happen by selectively breaking the rules,
but beware to the mere mortal who tried
it. So we carried on the tradition of pads
everywhere. All broadcast circuits started
and ended at 600 ohms.
And then op-amps came along…suddenly,
all input impedances are bridging,
and output impedances are so close to zero
that few worry anymore about the evils
of double- and treble-loading. Split pads
and bridging pads are no longer necessary…generally
you just hook up the inputs
and the outputs and plug the whole
works in. Very forgiving, and a hell of a
lot simpler than wiring everything up
with pads.
But I want to talk about a situation
that you might find yourself in where
you’ll need to start worrying about impedance
again, or you’ll rue the consequences
—the good old telephone program line.
Even if the program line to your transmitter
is a digital circuit, it most likely has
an analog loop between your studio and
the nearest telephone central office. At
the C.O., the phone company will equalize
the circuit, then it’ll go into some kind
of A/D, and from there it could go on a
microwave carrier, or fibreoptic link, or
copper T1 or HDSL, or a combination of
all of these, to get to your transmitter site.
In B.C. the phone company likes to run
HDSL or T1 right to the transmitter site.
There, it runs through a D/A converter to
your equipment. But we’re getting ahead
of ourselves—back to the analog loop
and the telco equalizer.
For the first 150m or so, a twisted pair
just looks like a pair of wires. Beyond
that, in addition to copper resistance, we
have series inductance and parallel capacitance,
which gives us your typical lowpass
filter. The audio response of the
analog loop rolls off at the high end. The
telco equalizer is adjusted to extend and
smooth the passband response. But how
is the response at the input of the equalizer
affected by the value of R, the source
impedance of the generator?
Here’s the key—telco engineers will
adjust the equalizer at the C.O. for flat
response using a 600-ohm source. When
you connect your modern processor,
with its 30-ohm buildout resistors, to the
line it acts like a 60-ohm source. I have
seen circuits that measured up 12 dB at 10
kHz because of this! The amount of the
effect is determined by the length of the
analog loop before the equalizer, with
longer loops causing larger HF peaks. Many
engineers will run the processor output
through a repeat coil, or 600:600 ohm
transformer, before leaving the studio.
Very nice, but it won’t do you a bit of
good here—the repeat coil, true to its
name, presents the 60-ohm source with
an image of what it sees. The really nefarious
element of this problem is that if
you suspected the line was poorly equalized
you’d likely patch in a 600-ohm generator,
which would measure this circuit
as flat. Only if you fed tone through the
processor, in the proof position, would
you truly see the problem.
The solution is quite simple—either
add buildout resistors in series with the
processor output tip-and-ring connections,
to make up a total of 300 ohms/leg
(when added to the internal buildout resistors
inside the processor), or run the
output through a 600-ohm pad of 10 dB
or so. (Ah, once again we witness the universal
curative properties of pads!)
And keep the repeat coil in the circuit
—it does protect from that 48V battery
that the telco types are so fond of.
54 BROADCAST DIALOGUE

ENGINEERING
How stuff breaks
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
Last month’s column wound up with
the engineer’s lament—no matter
where you are, something’s always
trying to break on you! Like most sad
stories, that one’s completely true. The
good news is that there are predictable
patterns to components’ malfeasance. This
month, we catalogue their misdeeds.
We all know that transistors fuse
faster than the fuses that are there to protect
them. But fuses get tired, too, particularly
the slow-blow variety—from metal
fatigue in the expansion during each initial
surge, supposedly—and finally blow
when they shouldn’t.
Thermal problems cause intermittent
faults in rectifier bridges, too.
Dust particles are attracted to anything
at a high voltage potential. They’ll stick
and eventually provide a conducting path,
which will then carbonise and probably
blow to pieces. This is partially counteracted
because all physical connections,
meantime, are busy expanding and contracting
as they’re cycled, trying to work
themselves loose. Typically they’ll get hot
and burn before they open up completely,
though.
Electrolytic capacitors are always trying
to either leak or dry out. If they dry
out, they’ll intermittently go open. If they
leak, the corrosive electrolyte will proceed
to wreck any printed circuit board in the
vicinity. Printed circuit board material,
meanwhile, will gradually carbonise
under the influence of heat.
The heat generated by power carbon
composition resistors actually causes the
carbon granules inside the resistor to
regranulate over the years, causing the
resistance to drop over time. Of course,
in most circuits, this results in more current,
and more heat, etc., etc., until the
inevitable short. Usually after that they’ll
present a very high resistance—kind of
like they’re trying to reform for their previous
current-hogging ways.
Transmitting mica capacitors develop
a series resistance that increases over time,
often variable with ambient temperature.
The resistive component makes them get
hotter and hotter, until the inevitable
fire. The old style, with the white ceramic
coating, will sometimes contain themselves—the
newer black plastic ones will
usually spray a flaming rubbery plastic all
over the place until the transmitter overloads
and gives up. They smell bad, too.
Metal oxide varistors will always fail
by suddenly providing a dead short. Of
course, generally they’ll blow up when
this happens, blowing off the leads and
noisily restoring a nice open circuit that
means no harm to anyone. But then the
ex-varistor is no longer providing any
protection, either.
Mylar capacitors, or plate blockers, are
prone to pinholes hidden under the plate
bypass element. If they were easy to see,
there wouldn’t be any challenge!
Hollow doorknob capacitors heat up
until the solder connections to their terminals
melt. The solid red doorknobs
get pinholes or carbon traces, sometimes
internal, usually very hard to see.
Typically they’re very intermittent, too.
Oh joy!
Oil-filled capacitors generally leak, or
short out and explode. Tantalum capacitors
prefer the dead short. Disc ceramics
go “leaky”, developing a shunt resistance,
or just absorb water vapour and start
drifting in value.
High-tension wire will break down
from heat and ozone, eventually carbonising,
typically near one end. Carbon
traces can travel several inches at the
end, however. Neoprene insulation will
rot from heat and ozone, and flake off,
exposing the copper beneath.
An old trick of the high-power inductors
in the plate supply is to maintain
their inductance, but short a point in the
windings to the frame. You can sometimes
solve this by slipping last year’s
phone book under the frame, insulating
it from ground.
Ceramic tower guy-line insulators
(“eggs”) will develop carbon traces, then
start arcing, creating RF interference. The
fibreglass ones will break down in the
sun, absorb water, and arc until they’re
fully carbonised. Then they explode.
Old circuit breakers, like old engineers,
just get “tired” and start tripping
over nothing.
46 BROADCAST DIALOGUE

ENGINEERING
Radio redux –
tales of errant gensets
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
We left off last time while checking
the standby generator. Specifically,
is the engine block
warm from the block heater? These
heaters often fail, and many diesel gensets
have trouble starting if completely cold.
It’s always a good idea to exercise the
generator periodically, and although it’s
tempting to run it without its load (no
interruptions and surges for the transmitter
to cope with), that really doesn’t test
much except the starter motor and battery
unless the load is connected. In fact, it is
best if the generator is fully loaded up.
The best way to test, though possibly
not the most convenient, is to turn off
the main hydro breaker. This, after all, is
your best simulation of a complete hydro
outage. The generator should start up,
the load should transfer, and the generator
should fairly quickly settle at 60 Hz.
Don’t worry too much if the frequency
is one or two Hz off, but pay particular
attention if the generator continues “seeking”,
or changing speed. In excessive cases
the engine looks like it’s ready to leap off
its motor mounts. Problems of this nature
may indicate adjustments to the governor
are necessary. Time to call in the generator
specialists: some of the newer electronic
governors have as many as six or
seven controls, all interdependent, for
frequency, damping, response rate, sensitivity,
etc. Proceed with caution!
A good load test will run the generator
for an hour or so. Most of those I
informally polled liked to see a load test
every two to four weeks.
Stuff to Think About
A three-phase system should have full
three-phase failure sensing. While this
seems like a no-brainer, it’s surprising
what some genset suppliers will provide
in lieu of the full-meal deal…usually one
or two sensors. If you think about it, you’ll
realize that you shouldn’t accept anything
less than three sensors. A single sensor,
say between phase A and B, works unless
phase C is lost. A second sensor, between
B and C, will sense the failure of C. But
what if a tree leaning against your power
line shorts lines A and C together, blowing
the in-line fuse for C? The two-sensor
system will not detect this fault, and the
genset will not start. Been there, done that
…best to check that you’re sensing voltages
between all three legs of the line!
Delay on neutral is a deliberate hesitation
of a few seconds, between hydro
on-load and generator on-load. Normally
an extra-cost option, it can become important
if there are large motors, particularly
single-phase units, on-site and if the
transfer switch operates quickly. The stillrotating
motor stores energy (mechanically
the “flywheel” effect) from before
the transfer action—if the genset’s applied
energy is out-of-phase with the stored
energy, the resulting surge as the two
power sources rush to synchronize may
be large enough to intermittently pop
circuit breakers or generator exciter
diodes. Oh joy! Delay on neutral can be
added to avoid this problem. Some
modern advanced transfer switches contain
synchronizers, which add complexity
but permit a very rapid (

ENGINEERING
A safety primer for
transmitter visitors
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
As the years wear on, I’m beginning
to feel more and more like an oldtimer.
When I started out in this
business there was a lot of mentoring
going on, with chief engineers passing on
safe operating practices to their newer colleagues.
Nowadays, we more often work
alone—by necessity—which makes proper
safety procedure even more important.
Since transmitting tubes aren’t even discussed
in school anymore, let’s start with
a trip to a tube transmitter site.
Before You Set Out…
Does anyone know where you’re
going, and when you should be checking
back in? You should always alert someone,
whether from work or home, who
can come looking for you just in case
you have a nocturnal encounter with a
moose, for instance.
When You Arrive…
As you approach the site, always take
a quick glance around. I like to count the
guy wires on each tower to make sure
they’re all still connected. I got into that
practice after arriving at a site and tripping
over a downed guy wire. While
you’re looking up there you might as
well check that all the beacon bulbs are
working. And are there any signs of vandalism
or forced entry at the building?
In You Go…
We’ll assume that it’s a routine visit,
and not an emergency call. Everything in
its place? Transmitter visiting is such a
sensory experience: Does the blower sound
normal, or are belts or bearings wearing?
Do you smell anything you shouldn’t?
Part of troubleshooting is developing
your nasal skills, so that you can tell a
burnt resistor from a transformer or coil.
And if you ever smell a selenium rectifier
that has gone to meet its maker you’ll
never forget the stench!
How do the air filters look and roughly
what’s the inside temperature? Any signs
that water has leaked in anywhere?
If You Must…
Open the transmitter door, well, let’s
hope that you checked that the interlock
switches are working. Lock the transmitter
off by opening circuit breakers and
switches—make sure that the remote control
cannot re-energize the transmitter.
Of course you’ve removed all rings
and jewellery. Make sure you use that
shorting bar on anything you’re likely to
be touching. If you don’t have a shorting
bar use a big screwdriver and touch
those contacts to ground. When you’re
reaching around inside, develop the
habit of placing your other hand in your
pants pocket. The tendency to use that
hand to lean on the grounded cabinet
should be avoided, as any voltage that
you encounter would likely travel from
hand to hand across your heart, making
the experience that much more lethal.
Connections all clean and tight?
Insulators all clean and dry? Any sign of
arcing, or leaks or bulges on capacitors?
Belts in good shape? Bearings all lubed?
Well let’s get out of here then.
Close up the transmitter carefully, turn
on those breakers and switches. Listen
when you power up—often worn blowers
will choose this time to complain. Did
the air switch take a moment to close? If
it didn’t, maybe it’s stuck closed. And if
it’s stuck closed, it’s not protecting your
transmitter. Make a quick note in the
maintenance log of what you’ve done.
That’s it for this month. On your way
out, put your hand on the generator
block to see if the block heater’s still
warming it. Next trip, you’ll exercise that
genset for sure!
46 BROADCAST DIALOGUE

ENGINEERING
Radio redux—whither tomorrow’s
broadcast engineer?
BY DAN ROACH
THIS ARTICLE CAN BE DOWNLOADED FROM WWW.BROADCASTDIALOGUE.COM
Dan Roach works at S.W. Davis Broadcast
Technical Services Ltd., a contract engineering
firm based in Vancouver. He may be
reached by e-mail at droach@direct.ca.
Well, here we are in the new century,
and everything technical
is supposed to be better. All
our stations are automated; the cartridge
machines have all disappeared. Commercial
audio files automatically arrive in our
e-mail baskets, as if by magic. If we
desired, we could burn the files onto
audio CDs, full broadcast quality, which
would last for a century or so, for about
a buck per CD. Unbelievable!
Come to think about it, what exactly
do we mean by “broadcast quality?” The
phrase used to mean high quality, built
to last, and, usually, expensive. Nowadays,
“consumer quality” is often higher than
“broadcast quality”. But that’s okay, it’s
happening everywhere: a quality timepiece
used to connote high-quality workmanship,
as well as accuracy. Nowadays
a $40 Timex probably keeps time as well
as that Rolex you’ve always wanted.
Let’s face it: our old quest for highquality
technical standards that used to
burn up all of our engineer’s waking working
hours, has largely been reached: highquality
audio and video can be almost
trivial in the digital age.
Yet technical people are more overworked
than ever. The cartridge machines
disappeared, but in each one’s place up
sprouted half a dozen PCs. At most stations,
the engineer is now much more
involved in programming and operating
the radio station, because of the intricacies
of the automation system. Meanwhile,
the transmitter site has not gone away,
though it is much more likely to be
ignored while the engineer edits the
day’s logs, or tries to figure out why the
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automation insists on crashing each
Tuesday morning at 1:45.
The reliability of equipment may have
improved, but the station engineer seems
to be more essential than before. And
harder to replace.
Curiously, it’s not the new skills that
are hard to cover: there are, perhaps not
lots, but there are some computer-literate
potential radio station workers around.
But as colleges and technical schools have
increasingly focussed on information
technology, RF and component-level
troubleshooting skills have received progressively
less attention.
It’s surprising to many to realize that
broadcasting is one of the few remaining
areas of electronics where technicians
are expected to troubleshoot right down
to the component. We live in an age where
most electronic devices are more economically
repaired by swapping whole circuit
boards. And while that’s certainly true of
PCs, broadcast consoles and transmitters
are mostly too expensive to be repaired
that way. Component-level troubleshooting
and repair is an art all of its own—
an art at which fewer, as the years progress,
will be adept.
Broadcasters hastened the attrition by
largely eliminating assistant engineer
positions throughout the ‘80s and ‘90s.
Now the chief engineers are starting to
reach retirement age, and the skill shortage
is becoming more apparent to all.
What to do?
Well, we should start by encouraging
young technicians to enter broadcasting.
The field offers challenging work that is
far more varied than most technical employment.
And maybe it’s time to increase
the number of technicians on staff—if
they’re so busy, perhaps increasing their
number will help improve their lot.
Frankly, it’s probably the only way to create
an entry-level job in broadcast engineering
today.
And without entry-level technical
jobs, there will be no new broadcast
technicians.
44 BROADCAST DIALOGUE