Receive Board; Circuit Description; Alignment Procedure; Options - Circuit Descripition - Telex TR-200 Service Manual

RECEIVE BOARD
CIRCUIT DESCRIPTION
Signals from the receive antenna proceed through
3
tuned circuits, Q101, and 3 more tuned circuits
to mixer Q103. Oscillator Q102 is a Colpitts with
the collector tuned to the second harmonic. Y 101
operates on the fifth overtone with C112 and L107
acting as mode suppressor. From the mixer the
signal continues through FLlOl to second mixer
2. Connect the audio voltmeter and SINAD meter
from pin 3 or 4 of the P.C. board connector to
ground. Turn the volume control (R159) to its
halfway point. NOTE: K aligning with boards
separated, make the audio hookup from pin 6
to ground.
3.
Set the power supply for 9 volts and connect it
from pin 11 (+) to pin 10 (-) of the P.C. board
connector.
U ~ O I A . This downconverts the 10.7 MHz to 455
KHz.
After passing through FL102, the signal is
4. Set the generator deviation to+3
KHz
at 1
KHz.
limited and detected by UlOlB. UlOlB contains
Set the output level to 1 mV.
a quadrature detector which is tuned by L109.
5. Set the generator frequency to the receive fre-
UlOlC functions as a 16
KHz
bandpass filter for
quency. This is printed on Y 101 and stamped
operating the squelch. With no signal a large
into the rear case.
amount of noise is present at UlOl pin 11 and this
.
6 . AdjustL109 for maximum audio.
is rectified by D101, lowering the voltage at pin 12
to less than .65 volt. This switches pin 14 to ground
7- Adjust T101, L108, L109, L105, L104, L103,
and mutes the audio. When a signal is received, the
VC102 and VClOl in turn for best SINAD.
noise at UlOl pin 11 drops and causes the voltage
8. set the generator output to 1 u ~ .
at pin 12 to rise above .65 volt, releasing the clamp
,
on the audio. R122 adiusts the bias current through
9. Adjust R122 until the audio is squelched off.
R121, R120, and ~ i 0 1 and is used to set t i e
10. Reduce the power supply voltage to 7 volts.
squelch point. De-emphasis is provided by R117,
R125, and C128. U1A is an amplifier whose gain
11. Adjust R135 until LED 102 just comes on.
is controlled bq' the level of audio entering-the
rectifier at pin 4. As the level here increases, the
gain is increased and this results in a 2: 1 expansion
OPTIONS-CIRCUIT DESCRIPTION
characteristic, which reverses the processing done
in the transmitter. R159 is the user volume control
~t may be desirable in some instances to gate not
and U105 drives the headset.
only the audio on and off with the push-to-talk
button but also the transmitter itself. This would
be the case if several TR-200 units which were
ALIGNMENT PROCEDURE
E uipment Required:
b
Signal Generator
Audio Voltmeter
SINAD Meter
DC Power Supply
1. Solder one end of a 50 ohm coaxial cable from
the receive antenna pad to ground. Connect the
other end to the signal generator.
transmitting on the same frequency were being
used togeth~;--F~r-ths~pti~n,--R44, a jumper, is
removed and
46
installed.
For the TR-200 units which do not communicate
with a BTR-200 base station, but instead are used
with a mirror image TR-200, sidetone must be
added. Unlike the base station the TR-200 does
not retransmit the received signal. For this option
C51 and R46 are installed.