Circuit Description; Receiver Circuits - Icom IC-V80E Service Manual Addendum

SECTION 4.

4-1 RECEIVER CIRCUITS

RF CIRCUITS
The RX signal from the antenna is passed through the LPF,
antenna SW (D1 and D2) and limiter (D50), then filtered by
the tuned BPF (D9). The filtered RX signal is then applied
to the RF AMP (Q12). The amplified RX signal is filtered by
another tuned BPF (D11), then applied to the 1st IF circuits.
• RF CIRCUITS
D11
Q12
RF
BPF
AM P
1ST IF CIRCUITS
The RX signal from the RF circuits is applied to the 1st IF
mixer (Q13), to be mixed with the 1st local oscillator (LO)
signal generated by the VCO (Q76, D59–D61), resulting
in the 21.7 MHz 1st IF signal. The 1st IF signal is filtered
by the 1st IF filter (crystal filter; FI1 and FI3) to remove
unwanted signal, and applied to the 1st IF AMP (Q14). The
amplified 1st IF signal is applied to the 2nd IF circuit via the
limiter (D62).
• 1ST IF CIRCUITS
VCO
Q6
LO
AM P
Q76
D59-61
D62
Q14
IF
LIMI T
AMP

CIRCUIT DESCRIPTION

ANT
D1,D2
ANT
LPF
SW
D50
LIMI T
D9
BPF
D3,D4
Q4
TX/RX
BUFF
SW
114.300-152.300 MHz
LPF
FI1,FI3
XTAL
BPF
Q13:
21.7MHz
3SK293
2ND IF CIRCUITS AND DEMODULATOR
IC2 is the IF demodulator IC which contains the 2nd IF
mixer, 2nd IF AMP, FM detector, etc. in its package.
The signal from the 1st IF circuits is applied to the 2nd IF
mixer, to be mixed with the 2nd LO signal generated by the
reference frequency oscillator, resulting in the 450 kHz 2nd
IF signal. The 2nd IF signal is filtered by the external 2nd
IF filter (ceramic filter; FI2) to remove any unwanted signal,
and applied to the 2nd IF AMP. The amplified 2nd IF signal
is applied to the frequency demodulator circuit.
The demodulated AF signal is applied to the RX AF circuits.
• 2ND IF CIRCUITS
X1 IC1
REF PLL
OSC IC
(21.25MHz)
Q7
BUFF
IC10
SQLIN
D/A
DET
IC3D
HPF
RX AF CIRCUITS
The demodulated AF signal from the IF demodulator IC (IC2)
is passed through the HPF (IC3D), which separates the
voice and tone signals, AF line SW (IC4), and then adjusted
in level by the D/A converter (IC10). The level-adjusted AF
signal is applied to the AF power AMP (IC5). The power-
amplified AF signal is applied to the internal speaker or to
an external speaker.
• RX AF CIRCUITS
CHASSIS
SP1
IC5
J3
Q31,D27,D65
CLONE CLONE
BUFF
4 - 1
IC2
IF DET-IC
(MIX,IF-AMP,
NOISE-AMP,FMDET,
DET
SDET,SQLSW)
X3
SD,NOIS
CERAMIC
W/N
BPF
SW
FI2 Q83
Q53
TONE
LPF
FIL
WXALT CTCIN
AF1
AF2/MOD2
IC10 IC4
VOLIN
AF VOLOUT
D/A AF SWITCH
AMP
LPF