User's Manual

Antenna Switch
In receive, the diode D5 and D6 are reverse biased. L11 is now in circuit, passing the signal from the
antenna to the front end without signal loss.
Front End
The receiver signal is routed to pin 1 of the RF Front End module. It passes through the band pass
filter consisting of C800 to C808/L800 to L803.
Diode D800 serves as protection from RF overload from nearby transmitters.
The input signal is coupled to the base of Q800, which serves as an RF amplifier.
The output of Q800 is then coupled to a second band pass filter consisting of C814 to C822 / L804 to
L806.
The output of the front end module, pin6, is then coupled to the double-balanced mixer IC8.
The receiver front end module is factory pre-tuned and requires no adjustment.
Repair is effected by replacement of the entire module.
First Mixer
IC8, 2-pole crystal filters XF1 and XF2 and coils L16 and L18 form the First Mixer and First IF
Filter.
IC8 is a self-contained double balanced mixer. The RF signal, from the front end is applied to pin 4
and the VCO local oscillator signal is applied to pin 1.
The difference frequency of 45 MHz is taken from pin 5 and is filtered by the crystal filters XF1 and
XF2. The tuned circuits L16 and L18 and associated components provide matching of the crystal
filters to ensure a good pass-band response and selectivity.
The IF signal is amplified by Q24 and passed to the FM Detector IC.
Second mixer, Second IF, FM detector
The output of the IF amplifier is fed into the narrowband FM IF Integrated Circuit, IC6 (MC3371).
This is a single conversion FM receiver which contains the second mixer, second IF amplifier, and
FM detector.
PAGE 10