Receiver Circuits - Icom IC-80AD Service Manual

SECTION 4.

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).
• RF CIRCUITS
To 1st mixer
D203 D203
(IC900)
for A BAND
BAND BAND
SW SW
D256
D254,255
BAND
BPF
SW
Q301
D311
D306-309
BAND RF
SW AMP
D405
RF
SW
D508
RF
SW
D606
D604,605
BAND
BPF
SW
D706
Q701
BAND
SW
All manuals and user guides at all-guides.com
CIRCUIT DESCRIPTION
L202,203
Q200
C205-9 D201
D202
RF BAND
LPF
AMP SW
D251
Q250
D252 D250
D253
RF BAND
BPF
AMP SW
Q300
D304,305
D310
RF
BPF BPF
AMP
Q401
D402,403 D401
D404
RF
BPF BPF
AMP
Q500
D504,507
Q501
D503
RF
BPF
AMP
Q601
Q600
D601,602
D603
RF
BPF
AMP
Q700
D703,704 D 700
D705
RF RF
BPF ATT
AM P AMP
• 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.
0.5−30 MHz
L200,201
C201-204
D200
BAND
LPF
SW
30−76 MHz
174−260 MHz
L302,303
C306-310
D303 D302
BAND BAND
HPF
SW SW
76−118 MHz
L300,301
D301 C301-305 D300
BAND BAND
LPF
SW SW
118−174MHz
Q400 D400
RF BAND
AMP SW
260−350 MHz
470−600 MHz
D500
D501,502
RF BAND
BPF
AMP SW
350−470 MHz
L600,608
C600-602,630,631 D600
RF BAND
HPF
AMP SW
L8,9
C18-20
HPF
4 - 1
From the VHF TX
Tx: 144.000−148.000 MHz
circuits
L1-3
L4,C7-9 C1-6
ANT
LPF
LPF
SW
Q1,3,D6-8
From the UHF TX
circuits
L5-7
C10-14
ANT
HPF
SW
Q1,2,150
Tx: 430.000−450.000 MHz
D1,3,4,10,151,160
RF UNIT
600−1000MHz