Receiver Circuits - Icom IC-F8100 Service Manual

SECTION 4.

4-1 RECEIVER CIRCUITS

RF CIRCUIT (PA AND MAIN UNITS)
The RX signal from the antenna is passed through the
SWR detect circuit (PA UNIT; D5001, D5002), TX/RX line
SW (PA UNIT; RL5001) and LPF (PA UNIT; L5001, L5002,
C5101–C5105), and then applied to the MAIN UNIT.
The RX signal from the PA UNIT is passed through or
bypassed the attenuator circuit (MAIN UNIT; R1103, R1106,
R1108), RX mute SW (MAIN UNIT; Q1101, D1107), TX/RX
line SW (MAIN UNIT; D1108), and then applied to the filter
circuits.
The RX signal is passed through an LPF or one of BPFs,
depending on the operating frequency, to remove unwanted
out-of-band signals. The filtered RX signal is applied to or
bypassed the preamplifier circuit.
The RX signal from the filter circuits is applied to or
bypassed the preamplifier.
When the Preamplifier function is activated, the RX signal is
amplified by the preamplifier (MAIN UNIT; Q1116, Q1117).
The amplified or bypassed RX signal is applied to the 1st
RX IF circuits.
• RF CIRCUIT
D1133
D1131
D1406
Q1116,Q1117
D1129 D1142
RF
AMP
0.03-1.59 MHz
D 1 1 2 0
LPF ATT
1.60-2.49 MHz
D1113
D1121
BPF HPF
2.50-3.99 MHz
D1114
D1122
BPF
4.00-5.99 MHz
D1115
D1123
BPF
6.00-8.99 MHz
D1116
D1124
BPF
9.00-12.99 MHz
D1117
D1125
BPF
13.00-19.99 MHz
D1118
D1126
BPF
20.00-29.99 MHz
D1119
D1127
BPF
MAIN UNIT
CIRCUIT DESCRIPTION
fc=30 MHz
LPF To the 1st RX IF circuits
D 1 1 1 2
D1106
TX
RX
D1108
Q1101
D1107
RX MUTE
20 dB
ATT
D5086,D5087
D5084,D5085
D5088,D5089
D5090,D5091
D5001
fc=32 MHz
D5002
SWR
LPF
DET
RL5001
RX
TX
TX circuits
PA UNIT
1ST RX IF CIRCUIT (MAIN UNIT)
The RX signal from the preamplifier circuit is applied to the
1st RX IF mixer (Q1404–Q1407) to be mixed with the 1st
RX LO signal, resulting in the 64.455 MHz 1st RX IF signal.
The 1st RX IF signal is amplified by the 1st RX IF AMP
(Q1810) and passed through the 1st RX IF filter (FI1401).
The filtered 1st RX IF signal is amplified by another 1st RX
IF AMP (Q1414), and then applied to the 2nd RX IF circuits.
• 1ST RX IF CIRCUIT
Q1414
D1411
To the 2nd RX D1408
IF
IF circuits
AMP
2ND RX IF CIRCUIT (MAIN UNIT)
The 1st RX IF signal from the 1st RX IF circuits is applied
to the 2nd RX IF mixer (D1812, D1813) to be mixed with
the 2nd RX LO signal, resulting in the 455 kHz 2nd RX IF
signal. The 2nd RX IF signal is passed through the trans-
former-coupled filter (L1446) and 2nd RX IF filter (FI1402),
and amplified by the 2nd RX IF AMPs (Q1415, Q1412 and
Q1413), and then applied to the 3rd RX IF circuits, through
the buffer (Q1411).
• 2ND RX IF CIRCUIT
Q1412
Q1411
Q1413
To the 3rd RX
IF
IF circuits
BUFF
AMP
3RD RX IF CIRCUIT (MAIN UNIT)
The 2nd RX IF signal from the 2nd RX IF circuits is applied
to the 3rd RX IF mixer (IC1402) to be mixed with the 3rd RX
LO signal, resulting in the 36 kHz 3rd RX IF signal.
The 3rd RX IF signal is passed through the 3rd IF SW
(IC1403) and LPF (L1454. C1550, C1553), and then applied
to the demodulator circuits on the DSP-1 UNIT.
• 3RD IF CIRCUIT
To the demodulator
circuits
LPF
3rd TX IF
4-1
64.455 MHz 1st RX IF
Q1810
FI1401
Q1404-Q1407 From the
D1405
XTAL IF
AMP
BPF
BW=15 kHz
D1403
1st RX LO signal
L1446
Filter
Q1415
FI1402
D1812
D1813
D1418 D1416
D1420
IF
CERAMIC
AMP
BPF
2nd RX LO signal
36 kHz 3rd IF
IC1403
IC1402
D1412 From the 2nd RX
IF circuits
3rd IF SW
3rd RX LO signal
RF circuits
From the 1st
RX IF circuits