Am Detector Circuits; 2Nd If And Demodulator Circuits - Icom IC-2730A Service Manual

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)
IC119
AM
Left band
DET OUT
AF circuit
SELECT FM
2ND IF AND DEMODULATOR CIRCUITS (Right band)
IC119
AM
Right band
DET OUT
AF circuit
SELECT FM
4-3
X200
Q200
38.4MHz
X3
12.8MHz
IC121
IF IC Left band
1st IF circuit
X102
WIDE/NARROW
D107,D108,D111,D112
LIF
CERAMIC CERAMIC
BPF BPF
FI102 FI103
Q220 X201
45.9MHz
X3
15.3MHz
IC120
IF IC Right band
1st IF circuit
X101
WIDE/NARROW
D105,D106,D109,D110
RIF
CERAMIC CERAMIC
BPF BPF
FI100 FI101