Receiver Circuits - Icom IC-E2820 Service Manual

SECTION 4

4-1 RECEIVER CIRCUITS

RF CIRCUITS
<Left band>
• 118−174 MHz
The received signals from the antenna connector ANT-1
(J1) are passed through two LPFs (L101, 104, 108, C342,
346; L88, 92, 96, C318, 326, 330), then applied to the RF
amplifi er (Q37) via TX/RX switch (D75). The amplifi ed signals
are passed through the RX switch (RL2), attenuator (D68)
and tuned BPF (D55, 66), before being applied to another
RF amplifi er (Q33). The amplifi ed signals are applied to the
1st mixer (IC19) via the another tuned BPF (D41, 44) and
RX switch (D38).
While the diversity operation is activated, the received
signals are also input from ANT-2 (J2). The received signals
are passed through two LPFs (L103, 106, 109, C344, 348;
L90, 93, 98, C319, 327, 348), antenna switch (D65, 72) and
limitter (D64, 67), then applied to the RF amplifi er (Q39).
The amplified signals are applied to the RX switch (RL2),
and gone through the same process as the received signals
from ANT-1 (J1).
• 174−260 MHz
The received signals from the antenna connector (J1) are
passed through two RX switches (RL3 and D56) and the
tuned BPF (D51), then applied to the RF amplifier (Q34).
The amplified signals are passed through the BPF (D45),
attenuator (R139, 144, 147) and RX switch (D36) before
being applied to the 1st mixer (IC19).
• RF CIRCUITS
D38
RX
SW
D35
RX
SW
D10,
D7
RX
Left band
SW
D11
D8
D15,
RX
SW
Right band
D9
RX
SW
CIRCUIT DESCRIPTION
118−174 MHz
D55, D60
D41, D44
Q33
RF
BPF BPF
AMP
D54,
D40, D58
D43
Q32
RF
BPF BPF
AMP
118−174 MHz
375−550 MHz
D18, D20,
D12,
D14, D23, D26
D16
Q19
RF
BPF BPF
AMP
D19, D21,
,D13,
375−550 MHz
D24, D27
D17
Q20
RF
BPF BPF
AMP
D36 D45
RX
ATT BPF
SW
D37 D46
RX
ATT BPF
SW
Q18
RF
ATT HPF
AMP
• 260−375 MHz
The received signals from the antenna connector (J1) are
passed through two RX switches (RL3 and D57) and the
tuned BPF (D50), then applied to the RF amplifi er (Q35).
The amplifi ed signals are passed through the BPF (D465),
attenuator (R142, 143, 150) and RX switch (D37) before
being applied to the 1st mixer (IC19).
• 375−550 MHz
The received signals from the antenna connector (J1) are
passed through the LPF (L101, 104, 108, C342, 346) and
HPF (L77, 80, C296, 297, 303, 308), then applied to the
RF amplifier (Q28) via TX/RX switch (D53, 61, 62). The
amplifi ed signals are passed through the RX switch (RL1),
attenuator (D28) and tuned BPF (D19, 21, 24, 27), before
being applied to another RF amplifi er (Q20). The amplifi ed
signals are applied to the 1st mixer (IC19) via the another
tuned BPF (D11, 13, 15, 17) and RX switch (D8).
While the diversity operation is activated, the received
signals are also input from antenna connector ANT-2 (J2).
The received signals are passed through the LPF (L103,
106, 109, C344, 348), HPF (L95, 99, C329, 333, 338),
antenna switch (D69, 73, 74) and limitter (D63, 66), then
applied to the RF amplifi er (Q29).
The amplified signals are applied to the RX switch (RL1),
and gone through the same process as the received signals
from ANT-1 (J1).
RL2
Q38
D68 D76
RX
ATT
SW
Q37
RF
AMP
D70
ATT
D64,D67
D65,D71,D72
Q39
RF
LIMIT
AMP
Q29
RF
LIMIT
AMP
D63,D66
D69,D73,D74
D30
ATT
Q28
RL1
RF
Q30
AMP
D32
D28
RX
ATT
SW
174−260 MHz
D51
Q34
RF
BPF
AMP
260−375 MHz D50
Q35
RF
BPF
AMP
810−1000 MHz
Q23
RF
ATT
AMP
4 - 1
D59
D75
D78, D79
D77
TX/RX
LIMIT
LPF
SW
ANTENNA
ANT
LPF LPF
SW
ANT
HPF
SW
D53
D61
D48,D49
D62
TX/RX
LIMIT HPF
SW
D56
RL3
Q40
RX
D80
SW
RX
SW
D57
RX
SW
D22
RX
HPF
SW
ANTENNA
LPF