User's Manual

The input signal is conpled to the base of T201 which serves as an R F amplifier.
The output of T201 is then coupled to a second bandpass filter consisting of C 211 to C 212,L206
L207.
The output of the T201,is then coupled to the double-balanced mixer T202.
The receiver front end module is factory pre-tuned and requires no adjustment.
R epair is effected by replacement of the entire module.
F irst Mixer
T202,2-pole crystal filters F L 230 and F L231 and T215 form the F irst Mixer and F irst IF F ilter.
The difference frequency of 21.7 MHz is tak en from T202 and is filtered by the crystal filters
F L230 and F L231.The tuned circuits R 230 and R 235 and associated components provide
matching of the crystal filters to ensure a good pass-band response and selectivity.
The IF signal is amplified by T215 and passed to the F M D etector IC .
S econd mixer,S econd IF ,F M detector
The output of the IF amplifier is fed into the narrowband F M IF Integrated C ircuit,U240
(TA31136F ).This is a single conversion F M receiver which contains the second mixer,second IF
amplifier,and F M detector.
C rystal C R 240,connected to pin 1 of U240,determines the second local oscillator frequency.
In this case the crystal has a frequency of 21.25MHz.The first IF signal is applied to the mixer
and resultant frequency of 450K Hz,is the difference between the IF signal and second local
oscillator.
The 450K Hz IF signal is output from pin 3 and is applied to a 450K Hz band-pass filter.
The output of F L 240 is passed via pin 5 to a high gain IF amplifier coupled to the adjustable
quadrature detector TR 240.Any detected signal is produced at pin 9 of U240 and applied to the