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CIRCUIT DESCRIPTION
TRANSMIT BOARD
ALIGNMENT PROCEDURE
U50IC is an amplifier whose gain is controlled by
the level of audio entering the rectifier at pin 16.
As the level here increases, the gain is decreased
and this results in a 2:1 compression characteristic.
Pre-emphasis is added by U501B. R504, R505,
and C508 set this at 115uS. C531 rolls the response
off above 10KHz to further attenuate the 20 KHz
call signal (see Audio Board Circuit Description).
Q501 is a Colpitts oscillator with the collector
tuned to the third harmonic. T501, VVC501 and
VVC502 are added in selies with the crystal to
allow frequency modulation of the oscillator. The
oscillator is operated 10KHz below the series
resonant point of the crystal.
This improves
linearity at the expense of some stability. Q502 is a
trip1er and Q503 is a straight through amplifier.
The catTier frequency is thus nine times the crystal.
C529, C530 and L503 function as a low pass filter
and matching network.
3-2
EQUIPMENT REQUIRED:
o
RF POWER METER
o
FREQUENCY COUNTER
o
DC VOLTMETER
1. Connect the RF power meter and frequency
counter to the Transmit Antenna jack. Make
sure the Transmit switch on the reat· panel is set
the the Cont position.
2. Adjust T502, T503, T504, VC501, and VC502
for maximum power. Note: If adjustments are
severly out of alignment and no output can be
obtained, it may be necessmy to first adjust
T502 and T503 for maximum DC voltage at the
emitter of Q502. Then adjust T504 for maxi-
mum DC voltage at the emitter of Q503. Now
adjust VC50 1 and VC502 for maximum power.
3. Adjust T501 for the COlTeCt frequency:
Y501 Marking
Frequency
154T570
154.570
177T800
177.800
183T730
183.730
4. Repeat Steps 2 and 3 as necessmy.
5. Deviation
will
be adjusted in the audio board
alignment.
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