Radio Shack HTX-400 Service Manual page 8

(2) CIRCUIT FOR SUPPRESSION OF SPURIOUS RADIATION
THE TUNING CIRCUIT BETWEEN THE OUTPUT OF FINAL AMP Q101 AND ANTENNA, 4-STAGE
"PHI TYPE" NETWORK L101, L102, L103, L104, L105, L106, L107, C101, C102, C103, C104, C105,
C106 SERVES AS A SPURIOUS RADIATION SUPPRESSOR.
THIS NETWORK ALSO SERVES TO MATCH THE IMPEDANCE BETWEEN TX FINAL POWER AMP
Q101 AND THE ANTENNA.
(3) MAXIMUM MODULATION CONTROL
MODULATION SIGNALS ARE FILTERED WITH RC NETWORK AND GO TO THE AUDIO AMP
TO MAKE IT TO NOMINAL SIGNAL LEVEL TO ACHIEVE WANTED MODULATION.
IC806 PIN13 AND CORRESPONDING LEVEL LIMITING CIRCUIT CONTROL INCOMING AUDIO
SIGNAL WITH RV802.
ADJUSTING RV802 SHALL NOT EXCEED ¡ ¾ 5 .0KHz DEVATION UNDER.1KHZ AF 20dB UP
FROM 3KHZ DEVATION LEVEL INPUT.
RECEIVER
(1) RF AMP Q201 AMPLIFY RF SIGNAL FROM ANTENNA. THE AMPLIFIED RF SIGNAL IS FED
THROUGH TUNING BAND PASS FILTER SAW1, SAW2 TO THE BASE OF MIXER AMP Q202.
ALSO VCO SOURCE'S FREQUENCY 30.85MHz LOW THAN THE FREQUENCY OF EACH
CHANNEL IS SUPPLIED TO MIXER.
(2) THE SOURCE OF 30.85MHz FREQUENCY PASSED TUNING COIL L209 AND C217 IS FED
THROUGH MCF201/MCF202 TO IF AMP Q204.
(3) THE 450KHz FREQUENCY SIGNAL IS PRODUCED FROM IC401 BY MIXING THE OUTPUT
SOURCE OF MCF 201/MCF202 30.85MHz FILTER AND THE SOURCE OF 30. 4MHz
FREQUENCY FROM CRYSTAL OSCILLATOR X401.
(4) IC401 IS A FM DETECTOR WHICH PRODUCES AUDIO SIGNAL. THE AUDIO SIGNAL (IC401
PIN 9) IS FED THROUGH R412 AND C414 TO AUDIO POWER AMP (IC3).
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