IFR FM/AM-500, Maintenance Manual

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C. LEVEL DETECTOR CIRCUIT
The output level from the si gna1 amplifier circuit is sensed by a
level detector circuit to provide feedback to the modulator/
leveler circuit in the Generate Audio Module. Diode CR5102 and
capacitor C5116 form a level detector; and op amp U5103, with
diode CR5106 and capacitors C5117 and C5118, functions as an
amplifier. Potentiometer R5114 provides system adjustment.
D. RECEIVE ENABLE CIRCUIT
In the REC mode, the REC command turns on diodes CR5103, CR5104
and CR5107 to allow an attenuated sample of the transmitter power
to be routed to the IF Module. In the GEN mode, the diodes are
OFF, achieving isolation of the generated signal from the output.
E. POWER DETECTOR CIRCUIT AND 20 dB PAD
A generated signal leaving the signal amplifier circuit passes
through the RF LEVEL Attenuator on the Front Panel, then through
RN5101, which is a 20 dB pad in the Output Amplifier, before
being connected to the T/R jack. A signal entering through the
T/R jack passes through the 20 dB pad, then through the receive
enable circuit to the IF Module. A power detector circuit moni­
tors the incoming signal strength and provides feedback through
the Receive Audio power level adjustment circuit, then to the
Generate Audio mode power circuit to switch to the Receive mode
automatically. Diode CR5108 and capacitor C5124 form the power
detector.
7-12-2 THEORY OF OPERATION {S/N 3225 AND ON)
In the Receive mode, the output Amplifier Module couples any signal
received at the T/R Connector through a
20 dB
pad to the IF Module. In
the Generate mode, it amplifies the signal received from the IF Module
and
routes it to the Step Attenuator on the Front Panel. This signal is
then returned to the Output Amplifier for 20 dB additional attenuation
and routed to the T/R Connector.
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