1St If Circuits; Uhf Band; 2Nd If Circuits; Fm Demodulation Circuits - Icom IC-2730A Service Manual

1ST IF CIRCUITS

VHF BAND
• Left band
The received signal from the RF circuit and 1st LO signal are
applied to the 1st IF mixer (Q145) and mixed, resulting in the
38.85 MHz 1st IF signal.
The 1st IF signal is applied to the 1st IF fi lter (FI105), through
the band SW (D121).
• Right band
The received signal from the RF circuit and 1st LO signal are
applied to the 1st IF mixer (Q143) and mixed, resulting in the
46.35 MHz 1st IF signal.
The 1st IF signal is applied to the 1st IF fi lter (FI104), through
the band SW (D119).

UHF BAND

• Left band
The received signal from the RF circuit and 1st LO signal are
applied to the 1st IF mixer (Q146) and mixed, resulting in the
38.85 MHz 1st IF signal.
The 1st IF fi lter is applied to the 1st IF fi lter (FI105), through
the band SW (D122).
• Right band
The received signal from the RF circuit and 1st LO signal are
applied to the 1st IF mixer (Q144) and mixed, resulting in the
46.35 MHz 1st IF signal.
The 1st IF signal is applied to the 1st IF fi lter (FI104), through
the band SW (D120).
The fi ltered signal is amplifi ed by the IF AMP (Q137), and ap-
plied to the IF IC (IC120, pin 20).
1ST IF CIRCUITS
Q138 FI105
IF
XTAL
Left band
AMP
BPF
2nd IF circuit
38.85MHz
Left band 1st IF circuit
Q137 FI104
IF
XTAL
Right band
AMP
BPF
2nd IF circuit
46.35MHz
Right band 1st IF circuit
Left band 1st LO (VHF)
Left band VHF RF circuit
Q145
D121,D122
Right band 1st LO (UHF)
RX
SW
Right band VHF RF circuit
Q143
Left band 1st LO (UHF)
Left band UHF RF circuit
D119,D120
Q146
RX
SW
Right band 1st LO (UHF)
Right band UHF RF circuit
Q144

2ND IF CIRCUITS

• Left band
IC121 is an IF IC, which contains the 2nd mixer, limiter AMP,
noise AMP, quadrature detector, AM detector, AGC controller,
signal strength detector, and so on.
The 1st IF signal from the 1st IF AMP (Q138) and 38.4 MHz
2nd LO signal are mixed, resulting in the 450 kHz 2nd IF sig-
nal.
The 2nd IF signal is output from pin 3, and passed through
the ceramic fi lter (FI102: For FM-N or FI103: For FM), and
then applied to IC121 from pins 5 and 7.
• Right band
IC120 is an IF IC, which contains the 2nd mixer, limiter AMP,
noise AMP, quadrature detector, AM detector, AGC controller,
signal strength detector, and so on.
The 1st IF signal from the 1st IF AMP (Q137) and 45.9 MHz
2nd LO signal are mixed, resulting in the 450 kHz 2nd IF sig-
nal.
The 2nd IF signal is output from pin 3, and passed through
the ceramic fi lter (FI100: For FM-N or FI101: For FM), and
then applied to IC120 from pins 5 and 7.

FM DEMODULATION CIRCUITS

• Left band
The 2nd IF signal applied pin 7 is amplifi ed by the limiter AMP,
and then demodulated by the quadrature detector with the
ceramic resonator (X102).
The demodulated AF signal is output from pin 11, and then ap-
plied to the AF circuit, through the AF SW (IC119, pins 8, 9).
• Right band
The 2nd IF signal applied pin 7 is amplifi ed by the limiter AMP,
and then demodulated by the quadrature detector with the
ceramic resonator (X101).
The demodulated AF signal is output from pin 11, and then ap-
plied to the AF circuit, through the AF SW (IC119, pins 1, 2).
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