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tor. An RF gain control prevents overload of you should hea r a click indicating that the
the detector.
audio works. The most critical part is the
The detected signal passes through a filter IF alignment. Us ing a signal generator or
network which removes RF from the audio. a grid dip meter. couple a 21 MHz signal
The audio output stage has a choke in the into the grid of the 6AK5 mixer and tune
plate circuit which should be as large as pas- the 2 IF transformers for maximum signal. If
sible when used with phones. You could use the signal is too strong. it will whistle strongan
audio output transformer with a speaker. Iy. then you may have to slightly d rop the
instead .
screen voltage of the detector. The oscillator
The IF transformers are really no problem is then tuned to the correct frequency. L2. 3,
to bui ld. The coils are wound on two forms 8 and 4 are tuned as described earlie r and admm
(approximately ~ "} in diameter wh ich justed for maximum sensitivity.
arejoined together as shown in Figure 3. You T ransmitter tune-up is simple. T une
can substitute standard 21 MHz television IF the plate circuit of the oscillator to 50 MHz
transfo rmers.
and adjust the trimmer in the cathode and
The power supplies are standard and no plate coil for maximum output. Then insert
special precaution has to be taken. The two a less active crystal and adjust the cathode
filament windings are connected in se ries and trimmer so that it will oscillate without
rect ified to provide low voltage DC for the using excessive feedback . which can damrelay
and microphone. There is a resistor for age the crystals and cause poor stability.
adjusting the output voltage of the transmit- Next adjust the final coils for maximum
tcr. Th is should be set to about 200 volts in outp ut.
order to prevent damaging the 6AK5s. The The unit is now complete. After using
filament leads are shielded to prevent pickup it a while. you will be amazed at the perof
vibrator buzz when used in mobile opera- formance of such a simple rig. If you take
tion . The mechanical layout for the chassis care. you will have a statio n you can use at
are shown in Figures 6 and 7.
home. in the car. o r anywhere you want to
Testing and Alil/;nmenl
take it.1IJ
Check all voltages. When checking the
plate voltage of the 6AK5 detector tube. Tab " m- Now",be•. 1964 73 M ap "; " ,".
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