Icom IC-7800 Service Manual Download Page 14

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3 - 2

(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.

• 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.

1st LO Main

1st LO Sub

Crystal

filter

FI401,
FI402,
FI403

Main 1st mixer

IC1051,

Q1211, Q1212

Sub 1st mixer

IC1051,

Q1211, Q1212

2nd LO Main