Rx-B Circuit; Rx-A Or Rx-Only Circuits; 1St Mixer Circuit - Icom IC-7800 Service Manual

(2) 50–60 MHz (BPF AND RXPLL-A UNITS)
When [P.AMP] switch is set to [P.AMP 1] or [P.AMP 2],
the amplified signals from the DW amplifier (BPF unit;
Q901) are applied to the pre-amplifier2 (BPF unit; Q903)
or pre-amplifier1 (RXPLL-A unit; Q1209, Q1210) via the
P.AMP2_ON selectors (BPF unit; RL902, RL903) and
P.AMP1_ON selectors (RXPLL-A unit; RL1203, RL1206),
respectively. Pre-amplified or bypassed signals are applied
to the 1st mixer circuit after being passed through the low-
pass filter (RXPLL-A unit; L1217–L1219, C1244–C1250,
C1268).

• RX-B CIRCUIT

(1) 0.03–30 MHz (RXPLL-B UNIT)
The RF signals from the DIGISEL unit are applied to (or
bypass) the DW amplifier (Q1001) via the DW selectors
(RL1001, RL1002), and are then applied to the pre-
amplifier circuit.
When [P.AMP] switch is set to [P.AMP 1] or [P.AMP 2], the
signals are applied to the pre-amplifier1 (Q1007, Q1008) or
pre-amplifier2 (Q1006) circuit via the P.AMP_ON selectors
(RL1003, RL1006) and P.AMP selectors (RL1004, RL1005),
respectively. Pre-amplified or bypassed signals are applied
to the 1st mixer circuit after being passed through the low-
pass filter (L1052–L1054, C1053–C1057, C1067).
(2) 50–60 MHz (BPF AND RXPLL-B UNITS)
When [P.AMP] switch is set to [P.AMP 1] or [P.AMP 2],
the amplified signals from the DW amplifier (BPF unit;
Q961) are applied to the pre-amplifier2 (BPF unit; Q953)
or pre-amplifier1 (RXPLL-B unit; Q1209, Q1210) via the
P.AMP2_ON selectors (BPF unit; RL952, RL953) and
P.AMP1_ON selectors (RXPLL-B unit; RL1203, RL1206),
respectively. Pre-amplified or bypassed signals are applied
to the 1st mixer circuit after being passed through the low-
pass filter (RXPLL-B unit; L1217–L1219, C1244–C1250,
C1268).

3-1-4 1ST MIXER CIRCUIT

(RXPLL-A AND RXPLL-B UNITS)
The 1st mixer circuit mixes the receive signals with the 1st
LO signal to convert the receive signal frequencies into
a 64.455 MHz (main) or 64.555 MHz (sub) 1st IF signal.
The IC-7800 has four 1st mixer circuits for the dualwatch
function.
• RECEIVER CONSTRUCTION
Main 1st mixer
IC1051,
Q1211, Q1212
0.03 60.0 MHz
1st LO Main
Sub 1st mixer
IC1051,
Q1211, Q1212
0.03 60.0 MHz
1st LO Sub
FI401,
Main 2nd mixer
FI402,
IC1051,
FI403
IC1052
Crystal
filter
2nd LO Main
FI401, Sub 2nd mixer
FI402, IC1051,
FI403 IC1052
Crystal
filter
2nd LO Sub
3 - 2
• RX-A OR RX-ONLY CIRCUITS (RXPLL-A UNIT)
(1) 0.03–30 MHz
The filtered signals pass through the L1055, and are
then applied to the 1st mixer circuit (IC1051). The applied
signals are mixed with 1st LO signal from the RXPLL-A
circuit to convert into a fixed 64.455 MHz 1st IF signal.
The converted 1st IF signal is applied to the 50/HF selector
(IC1081, pin 1).
(2) 50–60 MHz
The filtered signals pass through the L1220, and are then
applied to the 1st mixer circuit (Q1211, Q1212). The applied
signals are mixed with 1st LO signal from the RXPLL-A
circuit to convert into a fixed 64.455 MHz 1st IF signal.
The converted 1st IF signal is applied to the 50/HF selector
(IC1081, pin 3).
The selected 1st IF signal passes through the low-pass
filter (L1058, L1060, L1062, L1063, C1061, C1062, C1064,
C1066, C1070, C1074, R1054), and is then applied to the
1st IF circuit.
• RX-B CIRCUIT (RXPLL-B UNIT)
(1) 0.03–30 MHz
The filtered signals pass through the L1055, and are
then applied to the 1st mixer circuit (IC1051). The applied
signals are mixed with 1st LO signal from the RXPLL-B
circuit to convert into a fixed 64.555 MHz 1st IF signal.
The converted 1st IF signal is applied to the 50/HF selector
(IC1081, pin 1).
(2) 50–60 MHz
The filtered signals pass through the L1220, and are then
applied to the 1st mixer circuit (Q1211, Q1212). The applied
signals are mixed with 1st LO signal from the RXPLL-B
circuit to into a fixed 64.555 MHz 1st IF signal.
The converted 1st IF signal is applied to the 50/HF selector
(IC1081, pin 3).
The selected 1st IF signal passes through the low-pass
filter (L1058, L1060, L1062, L1063, C1061, C1062, C1064,
C1066, C1070, C1074, R1054), and is then applied to the
1st IF circuit.
DSP-A
board
RXPLL-A UNIT
RXPLL-B UNIT
DSP-B
board
CHASSIS
PWR amp.
unit
IC140
MAIN unit