Icom ID-880H

4 - 1
• RF CIRCUITS
SECTION 4. CIRCUIT DESCRIPTION
LPF
HPF
BPF
RF
AM P
LPF
TX/RX
SW
BPF
BPF
HPF
RF
AM P
TX/RX
SW
RF
AM P
RX
SW
BPF
BPF
RX
SW
RX
SW
RF
AM P
RF
AM P
RX
SW
BPF
BPF
D59,68,75,77
From VHF TX circuit
From UHF TX circuit
To the 1st IF mixer (Q124)
To the 1st IF mixer (Q125)
<- To the 1st IF mixer (IC64)
<- To the 1st IF mixer (IC64)
D30,53,61,62,177
LIMITER
D78,D79
D41,D44,D60
Q19
Q33
<- 810-999 MHz
Q28
<- 420-550 MHz
<- 230-420 MHz
Q35
VHFLPF
UHFLPF
D16
D13
D12,14,23
D56
D57,58
D45,D51
Q34
D36
D18,D20
D9
<- 118-174 MHz
BPF1,2,3
BPF1,2,3
BPF2,3
BPF2,3
BPF1
BPF1
4-1 RECEIVE CIRCUITS
RF CIRCUITS
144 MHz BAND (118–174 MHz)
The RX signals (118–174 MHz) from the antenna are
passed through two LPFs and TX/RX SW for VHF band (D59,
68, 75, 77), and applied to the RF circuit.
The RX signals are passed through the limiter (D78, 79) and
BPF, and amplifi ed by the RF AMP (Q33). The amplifi ed RX
signals are filtered by tuned BPF (D41, 44, 60) to remove
unwanted signals, then applied to the 1st mixer (Q124).
The passband frequency of the tuned BPF (D41, 44, 60) is
tuned by the tuning voltage from the D/A converter controlled
by the CPU (IC25).
300 MHz BAND (230–420 MHz)
The RX signals (230–420 MHz) from the antenna are
passed through the LPF, HPF and TX/RX SW for UHF band
(D30, 53, 61, 62, 177), and applied to the RF circuit.
The RX signals are passed through the RX SW (D56) and
filtered by the tuned BPF (D57, 58) to remove unwanted
signals, then applied to the RF AMP (Q35).
The amplifi ed RX signals are fi ltered by another tuned BPF
(D45, 51) to remove unwanted signals, and amplified by
another RF AMP (Q34). The RF AMP (Q34) improves the
isolation between the 1st mixer (IC64) and the tuned BPF.
The amplifi ed RX signals are applied to the 1st mixer (IC64).
The pass-band frequencies of the tuned BPFs (D57, 58:
D45, 51) are tuned by the tuning voltage from the D/A
converter controlled by the CPU (IC25).
440 MHz BAND (420–550 MHz)
The RX signals (420–550 MHz) from the antenna are
passed through the LPF, HPF and TX/RX SW for UHF band
(D30, 53, 61, 62, 177), and applied to the RF circuit.
The RX signals are passed through the RX SW (D16) and
tuned BPF (D13) to remove unwanted signals, and applied
to the RF AMP (Q19). The amplifi ed RX signals are fi ltered
by another tuned BPF (D12, 14, 23) to remove unwanted
signals, then applied to the 1st mixer (Q125).
The pass-band frequencies of tuned BPFs (D13: D12,
14, 23) are controlled by the tuning voltage from the D/A
converter controlled by the CPU (IC25).
800 M Hz BAND (810–999 MHz)
The RX signals (810–999 MHz) from the antenna are
passed through the HPF, and applied to the RF AMP (Q28).
The amplifi ed RX signals are fi ltered by the tuned BPF (D18,
20) to remove unwanted signals, then applied to the 1st
mixer (IC64) via the RX SW (D9).
The pass-band frequency of tuned BPF (D18, 20) is tuned
by the tuning voltage from the D/A converter controlled by
the CPU (IC25).