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Number 15 0n your FHdbkk e.rd
Six Meter QRP Station
Who says we don't use tubes anymore?
by Tima Popovich ex-YUlFR
T
he unit described in th is article proved
the theory that it is possible to establish
contacts at quite res pectable distances with
very low power.
Designed primarily for mobile use . the sta ­
tion runs fro m a 6 volt battery. For 12 volt
operation. the healers will have to be rewired
and changes made in the power supply. An
AC supply is included, mak ing it a statio n for
all-a round use .
Before going into the details of construction,
here is a briefdescription of the various
pans.
T he T rans mitter
The oscillator is a Jones ci rcuit which,
compared with other circuits. furn ishes a
high range of potent harmonics. The crystal
is of the highest possible frequency so that
enough drive is available for the final. The
final uses push-pull 6AK5s whic h. at low
input, give I to 1% Walts of output. I used
6A K5s because of their low
heater drain (1 75 rnA) and
good high frequency cfficrency.
the final amplifie r. The microphone is coupled
to the 6AQ5 through a carbon microphone
transformer. The quality is good and
there is plenty of modulation .
Power Su pplies
There are two independent power supplies
in the transceiver. The mobile supply is a
conve ntiona l vi brato r supply delivering
about 200 volts at 80 rnA . The AC supply is
also convention al and delivers the same
voltages in addition to rec tified and filtered
low voltage DC for the operation of thc relay
and microphone .
Warm Up The Iron!
Now that I've given you a description ofthe
transceiver, the next step is to drag ocr the
soldering iron and begin the construction.
1be schematic for the transmitter and modulator
is shown in Figure I . The Jones oscillato
r is of the cathode feedback variety . The
feedback is caused by the RF voltage drop
across the RFC in the cathode. A small RF
choke in parallel with a 3- 30 pF trimmer is
used. The trimmer adjusts the amount of
feedback to compensate for the lack ofactivity
of some crystals. To adj ust this. use an
inactive crystal and set the trimmer so that the
oscillator cuts in smoothly and reliably. This
setting will be good for all other crystals.
The cho ke in the cathode consists of #28
wire close-wound I N on a slug-tuned *N
form . Thc crystal can eithe r be 12.5 or 16.5
MHz. The screen supply of the oscillator has
a form of voltage regulation caused by feed ­
ing voltage through a 10 k resisto r with an
N E2 o r similar neon connected from the
screen to ground. The plate ofthe oscillator is
connected to a transformer consisting of Ll
and L2. The final amplifier is a conventional
push -pull circuit with L2 as the grid coil and
L3 as the tank circuit.
Modulator layou t is not critical . the only
T he Receiver
The receiver is a superhet
with a regenerative detector.
This gives the best compromise
between battery d rai n
and pe r formance . W hen
possible. I used 6AK5s to
reduce battery drain. The
line-up uses a 6A K5 oscillator.
12An cascode RF amplifie
r . 6AK4 oscillator.
12AT7 cascode RF am plifie
r . 6A K5 I F amplifie r,
6AK5 regenerative detector.
and 6A K5 audio output.
T he output is e no ug h to
drive a pair of headphones
or a small. sensitive speaker.
If you want more out put.
you could use a 6AQ5 at the
cost ofhigher battery d rai n.
The ~ Iodulato r
The modulator is extremely
simple , consist ing
of one tube. A carbon microphone
provides enough
output to d rive a 6AQ5,
plate and screen modulating
50 73 Amateur Radio • June, 1989
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Figure 1. SChematic for the ORP transmitter and modulafor.
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