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Num~ 21 on your FHdback eard
ABOVE AND BEYOND
C.L. Houghton WB61GP
San Diego Microwave Group
6345 Badger Lake
San Diego CA 92119
10GHzARRL
Contest Preparations
In April, I covered the construction
of a tripod and microwave
dish antenna for use on 10 GHz.
This month I would like to continue
with local involvement and
where to get equipmenttooperate
on the microwave bands. The
prime goal is to prepare for the 10
GHz ARAl contest later this summer.
This month.ret's cover some
of the things that you can do in
your own area to enhance operation
on microwave .
At first I thought San Diego was
dormant until N61ZW and I started
to talk abOut cceraucne on the l0­
cal repeater and at swap meets.
This resulted in quite a few fellow
amateurs forming a common
interest forum, the San Diego Microwave
Group. Through discussions,
we began forming a common
bond , which has grown and
spread quite widely. Participation
in a local group stimulales interest
and helps us sort out data from
other parts of the country. This as·
sists us in experimenting.
As to equipment, you have bastcally
two choices : bUy the very
fine MIA COM Gunnptexer, or obtain
surplus microwave equipment
at swap meets or even possibly
for free.
SCrounging for Equipment
By scrounging, you can get
QRV on the 10 GHz microwave
band for next to nothing, The quality
is not as good as the MIA COM
nunnpiexers. but it will work well.
Go to your local burglar alarm and
electric door companies and try to
obtain some of the otder mi ­
crowave control units they no
longer use, since they're switch·
ing to I.R optical units ,
Pat AA6EG wrote to me questioning
the use of a peculiar type
of alarm unit and detector diode
current. see Figure 1 fOf details.
You can check the detector for in-­
jection with a meter (0 to 1 rnA) in
series with the detector diode and
ground. With the transmit source
on, you should observe a DC current
flowing in the detector. About
VHF and UHF Operation
the frequency of the transmi t
source to the ham band, usually
about 10.250 GHz, by lowering
the frequency adjust screw further
into the cavity about 1 to 2 turns.
The microwave unit is set in the
factory to around 10,525 GHz.
The only limiting factors with
surplus devices are the system
sensitivity and any gains associated
with detector noise and antenna
types. Rememberthe SOLFAN
types were intended to be short
range devices, but they work very
well for the small cost of obtain ing
them.
Transmitter output power is a
consideration , but you may be
surprised with what you can do
with 10 mW. Usually, with modest
transceivers and small horns, 25
miles is the limit. With larger dish
antennas, 200-mile contacts are
possible.
By the way, I still have a quantity
of 50 to 100 mW 10 GHz Gunn
devices availabte lor $5 each
postpaid.
Success Stories
Sieve KA0ZIl from Plymouth,
Minnesota, writes: " I had some
time off from work, so I called
some local automatic door companies.
I picked two out 01 the severallisted
because they were local
companies. I struck paydirt with
both calls. At one, the tech is going
to clean up the shop next week
and set aside all microwave units
he would otherwise toss out. The
other shop had two units for me!
One was an old SOlFAN with a
detector, and the other was a
small black box, like the ones
above the doors at the grocery
store. The kicker is that they bolh
work!"
,,,...­
...fOC".
- ,....
-
I
.~ .
c ,.
."- _/
Steve KAIZll goes on to say
that with two units, he WIll probably
rope Rusty NIHVW, a good
friend, into 10 GHz operation.
Figure 2 is a sketch Steve provided
of one of his units, This unit is
very similar to the SO l FA N
devices. Power to the Gunn diode
is positive.
With 5 volts positive on the
Gunn, Steve was able to measure
about 1 rnA on the detector diode.
A little much, but still OK for a
transceiver . Connecting the detector
to a monitor receiver, Pat
was able to detect his fing er
movement in front of the cavity
while monitoring on the receiver.
For a Doppler radar device, connect
your detector diode to a small
audio amplifier. The low trequency
sound you hear is the microwave
Doppler signals returning,
As a mailer of fact, the radar
devices the police use are very
similar. They have circuits that
measure only the low frequency
audio tone (Doppler) to indicate
your speed. It's a direct corretalion.
For a speed of about 35 miles
per hour, the audio Doppler returned
is about 1085 Hertz. This
works out to about 31 Hertz per
mile per hour.
Se«ing the Frequency
The biggest problem remaining
is to set the frequency so that your
coeraucn is within our amateur
bands. I have received letters
from seve ral amateurs without
test equipment, who are trying to
set the frequency. Without test
equipment, it can be quite bothersome.
I am willing to set up cavities
sent to me in the mail (provided
return postage is included) to
the frequency desired, and I will
provide a voltage vs. frequency
spread calibration chart for the
unit. Ron Wicker WA5VJS has
take n me up on lhis offer and
shipped me two SOl FAN units.
I set both units on 10,250 GHz
, "
c "
Figure t, so GHz dual cavity from AA6EG, Each cavIty couples to its own horn
0.5 to 0.7 rnA is optimum. Adjust antenna, Anlenna gain is 1G- 12 dB.
70 73 Amateur Radio • June, 1989
,
with my HP counter. It remains to
be seen just how much bouncing
around the units will take for a
change in frequency in the postal
system. They were well-packed
and shoutd survive. Postage cost
less than I'd anticipated, at $2 for
a one-pound package . The rates
go up very quickly for a package
over two pounds.
The lnjector, described in the
January 1989 issue of 73 Magazine,
is an alternative to verifying
lrequency. Take a detector mount
and replace the normal detector
(1N23 diode) with a surplus varactor
and a 3 dB pad for DC return.
Inject your 2 meter HT on low power
(100 mW) in to the moont. The
varaetor should produce energy
radiating on 10 GHz. 146 MHz
times the 70th harmonic - 10.220
GHz, a good marker. Experiment
with surplus varactors for best results
on output. It will be very low
po wer, and close coupl ing i s
needed, but it works well.
So. cal.
Microwave Weekend News
There was quite a " urry of microwave
activity on 10 GHz narrow
band FM and SSB here in
southern California over our most
recent microwave weekend. The
contacts were from a location in
the L a k e Arrowhead , San
Bernardino mountains at Heaps
Peak. Phil W6HCC was operating
his 10 GHz system with about 1
Watt of power output, and had a
very noticeable signal. You could
turn your antenna some 20 degrees
away from the true path and
still copy him at a distance 01 over
100 miles with no troubte.
There were several other stations
operating remote to Phil
W6HCC at Heaps Peak. Chuck
WA6EXV was operating In the
desert to the east checking out
locat ions. Kerry N6I ZW , Ed
W60YJ, Art WA60YS, and l eon
WA5BNH from the San Diego Microwave
Group were operating on
Mt. Soledad in San Diego proper,
anchoring the southern end of the
100 mile test path.
The signals from W6HCC's rig
with 1 Watt output were so strong
they were pinning the s-meter on
the narrow band systems at Mt.
Soledad, 153 km distant. Kerry
N61ZW made contacts with both
FMand SSB over the 10GHz path
to Heaps with relative ease. His
system uses a two stage MGF­
1402 preamp with about 18 dB
gain and 4 dB noise figure. Provisions
are made in N6IZW's rig to
reverse the amplifier and use it in
the transmit mode, as it is linear