1St/2Nd Rx If Circuits (Rf-A Unit); Demodulator Circuits (Main Unit) - Icom IC-7410 Service Manual

1ST RX IF CIRCUITS (RF-A UNIT)
The RX signal from the BPF UNIT is passed through the
LPF, which removes unwanted signals (60 MHz and higher),
and then applied to the 1st RX IF mixer (Q721–Q724) to
be mixed with the 1st RX LO signal (64.485–124.455 MHz)
from the PLL UNIT, resulting in the 64.455 MHz 1st RX IF
signal.
The 1st RX IF signal is amplified by the 1st RX IF AMP
(Q741) and passed through one of the 1st IF fi lters (FI911;
FL-434, or optional FL-430 or FL-431), which has different
passband widths, according to the IF fi lter setting.
The fi ltered 1st RX IF signal is amplifi ed by the RX IF AMPs
(Q1051 and Q1071, Q1072), and then applied to the 2nd RX
IF circuits.
• 1ST RX IF AND 2ND RX IF CIRCUITS
I C1222 I C1222
To the demodulator circuits
Σ 90deg

DEMODULATOR CIRCUITS (MAIN UNIT)

The 2nd RX IF signal from the 2nd RX IF circuits is passed
through the RX mute SW (IC4604) and the balance-
unbalance converter (Balun; IC4602/IC4603), and then
applied to the CODEC (IC4651) to be converted into digital
audio signal.
The converted digital audio signal is applied to the DSP
(IC4001), and demodulated and processed.
• DEMODULATOR CIRCUITS
I C4461
I C4483
To the RX AF circuits
AMP
Q1071/Q1072
Q1051
I C1221 Q1201
D1102
IF IF
BUFF
AMP AMP
Q1251
I C1221
D1101
IF
BUFF
AMP
I C1121
BUFF
IC1121
BUFF 90deg
I C4001
DSP
IC1201
MAIN
CPLD
CPU
2ND RX IF CIRCUITS (RF-A UNIT)
The 1st RX IF signal from the 1st RX IF circuits is divided
into two paths, and then each signal is applied to the 2nd RX
IF mixers (the image reduction mixers; D1102/D1101) to be
mixed with the 2nd RX LO signal (64.491 MHz) from the PLL
UNIT, resulting in the 36 kHz 2nd RX IF signal.
The image reduction mixer removes image frequency
components by using two LO signals which are 90 degrees
phase-shifted from each other.
The 2nd RX IF signals are independently amplified by the
buffers (Q1201/Q1251) and IF AMPs (IC1221).
These amplifi ed 2nd RX IF signals are 90 degrees phase-
shifted and combined by the combiner (IC1222), and then
applied to the MAIN UNIT.
FI911
64.455MHz(BW=15kHz)
IF XTAL
ATT
AMP BPF
FL-430(Optional)
64.455MHz(BW=6kHz)
XTAL
BPF
FL-431(Optional)
64.455MHz(BW=3kHz)
XTAL
BPF
I C1121 Q1141
2nd RX LO
LO
BUFF ATT
AMP
The demodulated signal is applied to another CODEC
(IC4461) to be converted into analog AF signal, and then
applied to the buffer amplifi er (IC4483).
The buffer amplifi ed AF signal is applied to the CONNECT
UNIT.
IC4603
I C4651
LPF
IC4603
I C4602
LPF
IC1261
MAIN UNIT
3 - 2
Q721/Q722/
fc=60MHz
Q741
Q723/Q724
From the preamplifier circuits
IF
LPF
AMP
Q811
64.485~
LO
124.455 MHz
LPF
AMP
RF-A UNIT
I C4604
From the 2nd RX circuits
BUFF MUTE
1st RX/TX LO
LPF
LPF