Icom IC-R6 Service Manual page 10

1ST IF CIRCUIT (RF UNIT)
The RX signal from the RF circuit is applied to the 1st IF
mixer (IC1) to be mixed with the 1st LO signal from the 1st
LO VCO (Q528, Q529, D105 and D106), resulting in the
266.7 MHz 1st IF signal.
The 1st IF signal is filtered by the 1st IF filter (FI1), and then
applied to the 2nd IF mixer (Q523).
2ND IF CIRCUIT (RF UNIT)
The 1st IF signal is applied to the 2nd IF mixer (Q523) to be
mixed with the 2nd LO signal from the 2nd LO VCO (Q6 and
D17), resulting in a 19.65 MHz (for FM and AM modes) or
19.95 MHz (for WFM mode) 2nd IF signal.
The 2nd IF signal is filtered by the 2nd IF filter (FI3; for FM
and AM modes, or C507, C714 and C715; for WFM mode),
and then applied to the 2nd IF AMP (Q5).
The amplified 2nd IF signal is applied to the 3rd IF circuits.
• 1ST IF AND 2ND IF CIRCUITS
1st LO VCO
D42-D44
LO
SW
Q31 Q31
2nd LO VCO
X2 X2
D47,D50,D52
LO
LPF
SW
2nd Lo
1st Lo FM,AM: 247.050/286.350 MHz
WFM : 246.750/286.650 MHz
266.8-1099.695 MHz
FI1
D58,D59
MODE
BPF
SW
Q523
IC1
266.7 MHz
From the RF circuits
RF UNIT
FI3
D60,D61
Q5
XTAL IF
MODE
AM P
BPF
SW
19.650 MHz
To the 3rd IF circuits
BPF
19.950 MHz
3RD IF AND DEMODULATOR CIRCUITS
(RF UNIT)
The signal from the 2nd IF AMP (Q5) is applied to the IF de-
modulator IC (IC12) which contains the 3rd IF mixer, 3rd IF
AMPs and FM/AM demodulator circuits, etc. in its package.
The 2nd IF signal is applied to the 3rd IF mixer and mixed
with the 3rd LO signal from the reference frequency oscil-
lator (TCXO; X1), resulting in a 450 kHz (for FM and AM
modes) or 750 kHz (for WFM mode) 3rd IF signal.
The converted 3rd IF signal is passed through or bypassed
the ceramic BPF (FI2) to eliminate unwanted signal, and
amplifi ed by the 3rd IF AMP, then demodulated by the FM/
AM detector.
The FM detector employs a ceramic discriminator for the de-
modulation for FM mode and LC discriminator for the WFM
mode as a phase shifter. The AM detector employs a diode
detector circuitry.
The demodulated AF signal is applied to the AF circuits on
the LOGIC UNIT through the AF line SW (IC14).
• 3RD IF AND DEMODULATOR CIRCUITS
PLL
IC
X1
19.200 MHz
3rd Lo:19.2 MHz
From the 2nd IF circuits
IF IC
IC12
4 - 2
RF UNIT
D55
MODE
SW
FI2
CERAMI C
3rd IF
WFM: 0.750 MHz
BPF FM,AM: 450 kHz
D56
MODE
SW
IC14
To the AF circuits
AF line
SW
IC13
SQ L NOISE
AMP