Icom IC-80AD Service Manual - Section 4. Circuit
4 - 1
SECTION 4. CIRCUIT
DESCRIPTION
4-1 RECEIVER CIRCUITS
RF CIRCUITS (RF UNIT)
RX signals from the antenna are sorted by its frequency by
the filters and gone through RF circuits for each bands.
• 76 MHz and below
The RX signals are passed through two LPFs, ANT SW,
band SW and LPF. The RX signals are sorted by its
frequency by band SWs.
• 0.495–29.995 MHz
The RX signals are passed through the band SW (D201)
and LPF, and applied to tuned RF AMP (Q200). The
amplified RX signals are applied to the 1st mixer (IC900) via
two band SWs (D203 and D707).
• 30–75.995 MHz
The RX signals are passed through the band SW (D250) and
tuned BPF, and applied to the RF AMP (Q250). The amplified
RX signals are passed through tuned BPF, then applied to
the 1st IF mixer (IC900) via two band SWs (D256 and D707).
• 76–117.995 MHz
The RX signals are passed through two LPFs, ANT SW, band
SW (D300), LPF and another band SW (D301) in sequence,
then applied to the RF AMP (Q300) via the tuned BPF. The
amplified RX signals are passed through another tuned BPF,
then applied to another RF AMP (Q301). The amplified RX
signals are applied to the 1st mixer (IC900) via two band SWs
(D311 and D707).
• 118–173.995 MHz
The RX signals are passed through two LPFs, ANT SW, and
band SW (D400), then applied to the RF AMP (Q400). The
amplified RX signals are passed through the tuned BPF, and
applied to another RF AMP (Q401). The amplified RX signals
are passed through tuned BPF, then applied to the 1st IF
mixer (IC900) via two band SWs (D405 and D509).
• 174–259.995 MHz
The RX signals are passed through the LPF, HPF, ANT
SW, ATT, band SW (D302), HPF and another band SW in
sequence, then applied to the RF AMP (Q300) via the tuned
BPF. The amplified RX signals are passed through another
tuned BPF, then applied to another RF AMP (Q301). The
amplified RX signals are applied to the 1st mixer (IC900) via
two band SWs (D311 and D707).
• 260–349.995 MHz and 470–599.995 MHz
The RX signals are passed through the LPF, HPFANT SW,
ATT, BAND SW and tuned BPF in sequence, then applied to
the RF AMP (Q500). The amplified RX signals are passed
through another 2-pole tuned BPF, and applied to another
RF AMP (Q501). The amplified RX signals are then applied
to the 1st mixer (IC900) via two band SWs (D508 and
D707).
• 350–469.995 MHz
The RX signals are passed through the LPF, HPF, ANT
SW, ATT, band SW and HPF in sequence, then applied to
the RF AMP (Q600). The amplified RX signals are passed
through the tuned BPF, and applied to the RF AMP (Q601).
The amplified RX signals are passed through the BPF, then
applied to the 1st mixer (IC900) via two band SWs (D606
and D707).
• 600–999.990 MHz
The RX signals are passed through the HPF, ATT and
applied to the RF AMP (Q700). The amplified RX signals
are passed through the tuned BPF, and applied to another
RF AMP (Q701). The amplified RX signals are applied to
the 1st mixer (IC900) via the band SWs (D706 and D707).
The RF attenuation which reduces RX signal level to –10 dB is
carried out by D5, D9 and D701, by turning these PIN diodes
ON using "ATT" signal.
RF
AMP
ANT
SW
RF
AMP
RF
AMP
LPF
BAND
SW
BPF
BAND
SW
RF
SW
RF
AMP
RF
SW
LPF
BAND
SW
BPF
RF
AMP
HP F
BPF
HP F
BPF
BAND
SW
RF
AMP
LPF
BAND
SW
RF
AMP
RF
AMP
BPF
LPF
RF
AMP
BAND
SW
ATT
LPF
BAND
SW
BPF
BPF
BAND
SW
RF
AM P
ANT
SW
BAND
SW
BAND
SW
BAND
SW
BAND
SW
BPF
BAND
SW
BAND
SW
BPF
BAND
SW
BPF
RF
AMP
RF
AMP
HP F
BPF
Q1,2,150
D1,3,4,10,151,160
Q1,3,D6-8
RF UNIT
D304,305
Q601
D604,605
D606
D400
Q401
Q701
D402,403
D405
D200
D250
D254,255
D508
D253
D705
D603
D311
Q400
Q700
D201
Q500
D252
D600
D300
Q300
D302
D401
D703,704
D404
D706
D500
Q200
D503
D251
D256
Q600
D301
D306-309
Q301
D303
D 700
D501,502
D203
BAND
SW
D203
D504,507
Q250
Q501
D202
D601,602
To 1st mixer
(IC900)
for A BAND
From the VHF TX
circuits
From the UHF TX
circuits
D310
0.5−30 MHz
30−76 MHz
Tx: 430.000−450.000 MHz
Tx: 144.000−148.000 MHz
174−260 MHz
76−118 MHz
118−174MHz
470−600 MHz
260−350 MHz
350−470 MHz
600−1000MHz
HP F
L1-3
C1-6
L4,C7-9
L200,201
C201-204
L300,301
C301-305
L600,608
C600-602,630,631
L8,9
C18-20
L302,303
C306-310
L202,203
C205-9
L5-7
C10-14
• RF CIRCUITS