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4-3
AM DETECTOR CIRCUITS
• Left band
The 2nd IF signal applied from pin 5 is amplifi ed by the IF
AMP, and then demodulated by the amplitude detector in the
IF IC (IC121).
The demodulated AF signal is output from pin 14, and
then applied to the AF circuits, through the AF SW (IC119,
pins 11, 10).
In the AM mode, the AGC circuit in the IF IC automatically
adjusts the gain of RF AMPs (Q18 and Q20) and 1st IF AMP
(Q138), to keep the signal level constant.
The demodulated AF signal is applied to the RX AF circuit.
• Right band
The 2nd IF signal applied from pin 5 is amplifi ed by the IF
AMP, and then demodulated by the amplitude detector in the
IF IC (IC120).
The demodulated AF signal is output from pin 14, and then
applied to the AF circuits, through the AF SW (IC119, pins
4, 3).
In the AM mode, the AGC circuit in the IF IC automatically
adjusts the gain of RF AMPs (Q17 and Q19) and 1st IF AMP
(Q137), to keep the signal level constant.
The demodulated AF signal is applied to the RX AF circuit.
2ND IF AND DEMODULATOR CIRCUITS (Left band)
BPF
CERAMIC
BPF
CERAMIC
X3
DET OUT
SELECT
IF IC
FM
AM
Left band
1st IF circuit
Left band
AF circuit
LIF
WIDE/NARROW
12.8MHz
38.4MHz
X200
Q200
IC119
IC121
D107,D108,D111,D112
FI102
FI103
X102
2ND IF AND DEMODULATOR CIRCUITS (Right band)
BPF
CERAMIC
BPF
CERAMIC
X3
DET OUT
IF IC
WIDE/NARROW
SELECT
15.3MHz
AM
FM
Right band
AF circuit
Right band
1st IF circuit
RIF
45.9MHz
X201
Q220
IC120
IC119
D105,D106,D109,D110
FI100
FI101
X101