Icom IC-V80E, Service Manual Addendum

Page: 45 / 65

4 - 1
• RF CIRCUITS
• 1ST IF CIRCUITS
• 2ND IF CIRCUITS
• RX AF CIRCUITS
SECTION 4. CIRCUIT DESCRIPTION
ANT
LPF
BPF BPF
ANT
SW
RF
AM P
T1
T2_T3
LIMI T
D1,D2
D50
D9
D11
Q12
LPF
TX/RX
SW
BUFF
LO
AM P
IF
AMP
BPF
XTAL
D3,D4
Q4
Q6
FI1,FI3
Q14
Q76
D59-61
Q13:
3SK293
114.300-152.300 MHz
21.7MHz
VCO
LIMI T
D62
PLL
IC
BPF
CERAMIC
D/A
X3
HPF
LPF
BUFF
CTCIN WXALT
REF
OSC
X1
IC1
IF DET-IC
(MIX,IF-AMP,
NOISE-AMP,FMDET,
IC2
FI2
SDET,SQLSW)
(21.25MHz)
IC10
SD,NOIS
TONE
FIL
Q53
SQLIN
DET
DET
Q83
W/N
SW
IC3D
Q7
SP1
AF
AMP
D/A LPF
J3
VOLOUT
VOLIN
CLONE
BUFF
Q31,D27,D65
CLONE
AF SWITCH
IC4
AF2/MOD2
AF1
IC10
IC5
[EXT. SP]
CHASSIS
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.
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).
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.
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.