User's Manual

First local oscillator signal is supplied to Gate 2 of Q102 form the PLL circuit through C126 to convert
the RF signals into 21.4MHz first IF signal.
* IF CIRCUIT
The first IF signals from Q102 are fed to the matched pair crystal filter XCF101, then IF signals are
amplified in Q103. And those signals are fed to U401 which is composed of the second local oscillator,
second mixer, limiter amplifier, quadrature detector and active filter circuit. The second local oscillator at
20.945MHz with X402,and is fed to the second mixer with the first IF signals to convert into 455kHz
second IF signals..
The second IF signals leave through pin 3,and are fed to external ceramic filters FL401 which has
excellent selectivity, then fed to U101 (pin 5) again to be amplified and detected.
The detected AF signals are output from pin 9.
* AUDIO AND SQUELCH CIRCUIT
The detected audio signals are put through a 6dB/oct de-emphasis circuit made up of C507 and R519.
The signal is then applied to audio power amplifier U505 through the volume control U507 to obtain
enough power to driver the speaker.
Part of the recovered noise signal is fed to the integrated operational amplifier inside U401 which, with
C403,R405, C405, C404,R406 makes up an low pass filter . The DC signal detected by U401 (pin13)
reaches the integrated DC amplifier in U101 which has hysteresis to prevent jitter. The sensitivity of
squelch is adjusted by U2.
4) HAND FREE
It connects the telephone to jack J2 and checks the connection in PIN4 of U503. During the calling, it turns
MONITOR switch of Q506, Q507, Q508, Q509 off, then RF stops
5) AUDIO IN
Jack J506 receives external AUDIO, and amplifies in U505. When RF signal is received, AUDIO IN switch of
U504 is off, then it receives RF signal.
OPERATION
Please refer to the user’s manual for details
HJC-PMR X2 user’s manual
1. description