Icom IC-7600 Service Manual page 11

1ST RX IF CIRCUITS (RF UNIT)
The RX signals from the PREAMP BOARD are applied
to the splitter (L904) to divide the received signals for
dualwatch operation.
The separated RX signals are passed through the LPF
which removes unwanted signals (60 MHz and higher), and
amplifi ed by the RF AMP (Main readout; Q1201, 1202/Sub
readout; Q1001, 1002), then applied to the 1st RX IF mixer
(Main readout; Q1203–1206/Sub readout; Q1003–1006).
The RX signals are converted into the 1st RX IF signal by
being mixed with 1st RX LO signals (64.485–124.455 MHz)
from the PLL UNIT.
The converted 1st RX IF signals are passed through the
2-staged attenuator (Main readout; D1201–1203/Sub
• 1ST RX IF CIRCUITS
D3702
D3701
Q3601 3603
To the 2nd RX IF
IF
circuits
LPF
AMP
MAIN UNIT
2ND RX IF CIRCUITS (MAIN UNIT)
The 1st RX IF signal from the 1st RX IF circuits is divided
into two paths, and each signal is applied to the 2nd RX
IF mixers (Image reduction mixer; D3202/D3201) to be
converted into the 2nd RX IF signal, by being mixed with the
2nd RX LO signal (64.494 MHz) from the PLL UNIT.
The image reduction mixer removes image frequency
components by using LO signals which are 90 degrees
phase-shifted from each other.
The converted 2nd RX IF signals are amplifi ed independently
by the buffer (Q3202/Q3201) and IF AMP (IC3203).
These amplifi ed 2nd RX IF signals are 90 degrees phase-
shifted from each other by the phase shifter (IC3202; pins
8-10, pins 12–14). These phase-shifted 2nd RX IF signals
are combined by the combiner (IC3202; pins 5–7) to be
converted into the 3rd RX IF signal.
• 2ND RX IF, 3RD RX IF AND DEMODULATOR CIRCUITS
<- RX AF <-Analog
IC4301
IC4401
To the AF circuits
BALUN D/A
FI6001
XTAL
BPF
3K
L1018
D601
MCF-N HYBRID
COMBINER
BOARD
D1551
FI5001
XTAL
BPF
6K
MCF-M
TX CIRCUITS
BOARD
FI7001
XTAL
BPF
15K
MCF-W
BOARD
<-Digital
IC4001,
IC5001 IC4004 IC4002 IC3002
DSP
A/D BALUN LIMITER
readout; D1001–1003) which adjusts the balance of both
1st RX IF signals, and amplified by 1st RX IF AMP (Main
readout; Q1208/Sub readout; Q1008).
These amplified 1st RX IF signals are combined by the
hybrid combiner (L1018), and applied to the 1st IF filter
circuits.
The combined 1st IF signal is passed through one of the
1st IF filters on the MCF-N/-M/-W BOARDS which has
different passband widths. The fi lter to be passed through is
according to the IF fi lter setting.
The fi ltered 1st RX IF signal is applied to the RF UNIT again,
and passed through the LPF and amplified by the RX IF
AMP (MAIN UNIT: 3601–3603).
The amplifi ed 1st RX IF signal is then applied to the 2nd RX
IF circuits.
<-1st RX IF
Q1201
D1201,1203,1204
Q1202
Q1208
1st RX IF mixer
IF PIN DIODE
AMP
ATT
Q1203-1206
<-1st RX IF
D1001-1003
Q1008
1st RX IF mixer
IF
PIN DIODE
AMP
ATT
Q1003-1006
1st RX LO signals
1st RX LO signals for main readout
(64.485-124.455 MHz)
for sub readout
(64.485-124.455 MHz)
RF UNIT
The converted 3rd RX IF signal is amplified by the 3rd IF
AMP (IC3201), and passed through the limiter (IC3002) and
balance-unbalance converter (Balun; IC4001/IC4002), then
applied to the demodulator circuits.
DEMODULATOR CIRCUITS AND DSP (MAIN UNIT)
The 3rd RX IF signal from the 3rd RX IF circuits is applied
to the A/D converter (IC4004) to be converted into the digital
signal.
The converted digital signal is applied to the DSP (IC5001),
and demodulated and processed.
The demodulated signal is applied to the D/A converter
(IC4301) to be converted into the analog signal, then applied
to the buffer amplifi er (IC4401; pins 1–3).
The buffer amplified AF signals are applied to the RX AF
circuits.
MAIN UNIT
<-3rd RX IF
IC3202 IC3202
IC3201
90deg.
IF
PHASE
COMBINER
AMP
SHIFT
3 - 2
Fc=60MHz
<-Main readout path
RF
LPF
AMP
L904,905
From the PREAMP BOARD
SPLIT
Q1001
Fc=60MHz
Q1002
RF
LPF
AMP
<-Sub readout path
<-2nd RX IF
IC3203 Q3202 From the 1st
D3202
RX IF circuits
IF
BUFF
AMP
IC3203 Q3201
D3201
IF
BUFF
AMP
2nd RX LO signal
(64.491 MHz)