-- o ICOM

to have the filter at a low-level stage than
to amplify signals and create a bigger filtering
job. As a rule. MOSFET linear amplifiers
run far cleaner than bipola r types
simply because ar elevated signal levels. me
bipolar transistor is basically a non-linea r
device.
For RF amplification. use the following
guide 10 set up Ihe DV-1205S V-MOSFET
stage Q-14 in the main tran svener unit. The
level of drain current and ultimate power
output o f the stage 4 volts sets up a drain
current of 200 rnA. while 6 volts sets up 400
rnA . and 7 volts sets up 600 rnA. If you don' t
get an increase in power output with increased
drain current. you don't have enough
driving power 10 increase the power output of
the device. It isn't economical to increase the
drain current further. Si nce this project has
three MOSFET linear amplifier stages, set
the output levels for only what you require.
On the other hand, ifthe drive is much greater
than you need, don't worry about blowing
the FETs. since you can't hu rt them by overdriving
a little .
T est Eq uipment
In order to align and test the devices described
in this article , you need the following
test equipment.
I . A stable signal generato r or calibrated
o scillator and 50n adjustable attenuator
covering the appropriate RF range.
2 . A VHF-range RF vacuum tube voltmeter
or a good DC vacuum tube voltmeter
with UHF RF probe. (Solid state is fine. too.)
3 . An electronic frequency counter covering
the appropriate frequency range.
4 . A VHF grid dip meier to check coil
resonance. (NOI absolutely necessary if you
follow coil winding data closely . bUI it can be
a real aid.)
5. Capacity bridge 10 confirm small values
of capacity marked, and 10 set a given capacity
in a lesl circuit. (See Ham Radio , March
1980. page 54.)
6. A Bird Model43orotherpower measuring
device. and a 500 load (termination).
7. A multi-range VOM. II must be capable
of reading current to 10 amperes.
Where To Find Compo nent Parts at
Reasonable Prices
In this project you will use quantities of
miniature plated capacitors, various sizes of
compression capacitors, disc ceramic variables
and fixed capacitors. and dipped silver
micas (dog bone) components. Fixed disc
ceramic of 0.001 IJF are sprayed around the
source voltage lines as bypasses and as both
coupling and decoupling circuits. In circuits
requiring a degree of stab il ity, usc silver mica
caps. Johnson 2-12 pF, usually 8 plates total,
are used in stable RF circuits. These plated
and small. high quality Argo compression
types resonate coils.
All po.....dered iron and ferrite toroidal
cores and baluns are available from Amidon
Associates. You can buy the 8-pin DIN plug
from Kcnw ood. Get t.....o . The price ranges
from $2 10 $2.50 each. I bought my crystal
from Jan Crystals, 2400 Crystal Drive, Fort
40 73AmaleurRadio . June,lg89
Myers, Florida 33906-9989. Ordcr series
resonance O.ool accuracy and enclose a schematic
diagram of the oscillator circuit.
MHz Electronics lnc. , 3802 N. 27th Al·e. ,
Phoenix, Arizolla 85017 advertises in most
ham publications. They also have crystals.
transistors, and Unelco non-inductive capacitors
for the power amplifier. (Send for a
catalog.) Another excellent source for dipped
silver mica capacitors. miniature variables,
JFETs (I5C), 4067 (25 C) relays. and the
small heat sink 2N3866 is Hosf elt Electronics,
Inc. , 26/0 Sunset Blvd. , Steubem'ille ,
Ohio 43952. The 8-pin mike type plug and
jack are available from Henry Radio and
Radio Shack.
You will notice fu ll use of tuning capacitors.
This could add up to a nice piece of
change. Many of the stages in the receiver
What Is MOS-Power?
could be tuned temporarily with a good quality
fixed capacitor. Remove the capacitor and
measure a digital capacitance bridge. substituting
the capacito r ..... ith a good quality
dipped silver mica. Then compress or e xpand
the coils on the toroidal core until resonance
is re-established. This is a mildly complex
substitution I have seen described in many
publications.
Pans are also available at ham s.....ap meets,
and 1 have some items at very reasonable
prices. If you have questions o r comments,
feel free to write me. Enclose an SASE for
a response. Upon completing this project
(I wish to emphasize taking your time , step by
ste p), the gratification and pride you will feel
cannot be expressed on paper .
Look for the 6 meier rransvertcr project in
a subsequent issue of 73 magazine. DI
MOS-powe r FET transistors were developed by the Siliconix Transistor Manufacturing
Companymore than a decade ago. MOSFET transistors differfrom bipolar transistors. They have
a closer relationship to the vacuum lube, but are still different. You mighl ask, "Since they have
been withus forover a decade, why haven't we heard more about Ihem?" The answer is twofold:
(1) Low-power VMOs-FETs are widely used in industrial pulse applications, and (2) The
manufacturing industry of these devices is still woriting through the maze 01problems relating to
high-level procluctionwith power FETs.
We do have an earty generation of CMOStransistors and integrated circuitchips. S ihconil,the
originator of VMOS power transistors, sold its power MOS division to the MfA COM PHI
Corporation located in Torrance, California. Today they no tonger produce power FETs .
VMOS and UMOS FETs as described inthis project are N.(;hannel MOS power FETs operating
in an enhancement mode. The "V" in VMOS (vertical metal oxide semiconductor field effect
transistoq relates to the " V" structure ofthe gate, where me current has a vertical flow across the
short dimension of eecnc. The " U" in UMOS is a later truncationofthe " V" structure ot the Chip
that allows the transrsto- to produce higher levels of output power plus a very ccesetent level 01
gain over the frequency range.
VMOS ()( MOS power FETs are high impedance devices (possibly higher Ihan thai of the
vacuum tube]. At low frequencies, they are capacitive devices, rather than inductive, as
comparedto a bipolar device which is lowimpedance, and both input andoutput lookinductive. In
contrast.me dynamic impedance at the high frequencies is low. but several times higher than the
BPT. The bipolar device has a reputation of " thermal runaway." The trotter it gets, Ihe more
current it draws; the more current ncraws.tre hotter it gets, untilit destroys nsen. The MOS power
device has an opposite ettect. The hotter itgets. the less current it draws. until it Shuts nseu off.
Because of Ihe nonlinear gain 01a bipolar device (having high beta, or gain at low frequencies)
tapering off at the higher frequencies,the beta reaches a level 01 unity or me cut-off frequency.
Therefore, bipolar powertransislors are catagorized according 10 their specific frequency ranges
ofoperation. Should lower frequencies be induced onthe source power line, use special circuitry
in the power source to prevent the transistor from oscillating and burning up as a result of the
higher gain at the lower frequency.
VMOS, on Ihe other hand, have a very flal treque r'ICy gain. Usually this response is better than
± 1 dB across the range, including Ihe audio frequencies. It is common to see a 175 MHz device
used in a broadband 2- 30 MHz amplilier, for example. A significant deficiency of the bipolar
device is immediately noted as soon as you get out of the small signal level of operation. The
bipolar naoststoris basically a ClassC device andexceptionally nonlinear. Tousea bipolar power
device in the linear mode, the transistor must be bulldozer·style biased, wilh a silicon diode
somewhere in the voltage divider chain to hold the bias level. Also, the diode must be in ccetect
withthe transistce, sothat as the transistor heats up and the linear bias point level dolts, the diode
will also heat up and reestablish the linear bias point.
In comparison, a M05-power transistor withils exceedingly high resistance gate circuitcan be
positively or negatively biased for any class of operation: A, B, C, D, or E, unaffected by heal. In
that the gate circuit draws virtually zero current. the impedance of the bias supply is immaterial
and will slay exactly where it is originally set.
Most manufacturers state thai you cannot destroy a VMOSdevice byoverdriving. Somewill not
admil to s udden failure in a new design, such as a transient which can p!Jnch a hole through the
very thin barrier between thegateand source. However, the device will operate safely withinfinite
SWR to either its input oroutput-an elceptional Characteristic you can be very happy about . All
of the manufacturers test theirdevices with a 20:1 VSWR mismatch and 30:1 is called out on the
specification sreet. Sounds likeApril First!
Maximum junction temperature is specified at 200 6C (392°F). Typical powergainof the eevce
is 10 dB across the whole frequency range . I have seen devices specified as low as 7 dB and as
high as 14 dB to 1.4 GHz. With these impressive advantages over the bipolar, we can visualize a
faster demise for the bipolar transistor than even that of the vacuum tube.