Preamplifier Circuit (Main Unit); 1St Mixer Circuit (Main Unit); 1St If Circuit (Main Unit); 2Nd Mixer Circuit (Main Unit) - Icom IC-7000 Service Manual

The amplified signals are passed through the band switch
(D461) and then applied to the 1st mixer circuit (MAIN unit)
via J101 (MAIN unit).
D453–D456, D553, D554, D556 and D558–D560 are
varactor diodes that tune the center frequency of an RF
passband for wide bandwidth receiving and good image
response rejection.
When receiving the signals, higher than 129 MHz, are
received, the switching diodes (D555, D557) are turned off
by the control signal "2MBL" from the CPU (LOGIC unit;
IC1302) via Q2150, then the varactor diodes (D556, D558)
are disconnected to shift the filtering frequencies.

3-1-3 PREAMPLIFIER CIRCUIT (MAIN UNIT)

The preamplifier circuit amplifies received RF signals for
wide band frequency range.
When the preamplifier is turned ON, the RF signals
(HF/50 MHz bands) from the high-pass filters are applied to
the preamplifier (Q301) via the preamplifier switches (D301,
D302).
When the preamplifier is turned OFF, the RF signals (HF/50
MHz bands) are passed through the bypass switches (D301,
D303).
The amplified or bypassed signals are applied to the 1st
mixer circuit (IC401).

3-1-4 1ST MIXER CIRCUIT (MAIN UNIT)

The 1st mixer circuit mixes the received RF signals with the
1st LO signal to convert the receive signal frequencies to
the 1st IF frequency.
While receiving the HF/50 MHz bands signals, the amplified
signals from the preamplifier switch (D304) or the bypassed
signals from the bypass switch (D303) are passed through
the low-pass filter (L310, L312, C314, C316, C318, C320,
C322) and then applied to the 1st mixer circuit (IC401) via
the band switch (D305).
While receiving the VHF/UHF bands signals, the signals
from the VHF/UHF RF circuit (PA unit) are passed through
the low-pass filter (L309, L311, L313, C313, C315, C317,
C319, C321, C323, C325) and then applied to the 1st mixer
circuit (IC401) via the band switch (D306).
The applied signals are mixed with the 1st LO signal (124.517
–594.487 MHz) and convert into the 1st IF signal.
The 1st LO signal is generated in the DDS unit, and applied
to the 1st mixer circuit (IC401, pins 1, 6) after being ampli-
fied and attenuated at the 1st LO amplifier (IC421, pins 1, 4)
and the attenuators (R416–R418, R421–R423), respectively.
The converted 1st IF signal is applied to the 1st IF circuit.

3-1-5 1ST IF CIRCUIT (MAIN UNIT)

The 1st IF circuit filters and amplifies the 1st IF signal.
The converted 1st IF signal is
applied to the IF amplifier (Q502)
via RX switches (D502, D505).
The 124.487 MHz 1st IF signal
(except WFM mode) passes
through the crystal filter (FI601)
via the mode switches (D602,
D604), and the 134.732 MHz 1st
IF signal (WFM mode) passes through the bandpass filter
(L607, L609, C602, C606, C608–C610, C617, C618) via the
mode switches (D601, D603) to suppress out-of-band sig-
nals.
Then the filtered signal is applied to the IF amplifier (Q702)
and then applied to the 2nd mixer circuit (D801) via the RX
switches (D702, D704).

3-1-6 2ND MIXER CIRCUIT (MAIN UNIT)

The 2nd mixer circuit mixes the 1st IF signal with the 2nd
LO signal to convert into the 2nd IF frequency.
The amplified signal from the IF amplifier (Q702) is applied
to the 2nd mixer circuit (D801) and then mixed with the 2nd
LO signal (124.032 MHz) to convert into the 455 kHz (other
than WFM) or 10.7 MHz (WFM) 2nd IF signal.
The 2nd LO signal is generated in the DDS unit, and applied
to the 2nd mixer circuit (D801) after being filtered and
attenuated at the low-pass filter (L808, C816, C817) and the
attenuators (R801, R805, R806, R809–R811), respectively.
The converted 2nd IF signal is applied to the 2nd IF circuit.
3-1-7 2ND IF CIRCUIT (MAIN UNIT)
The 2nd IF circuit amplifies and filters the 2nd IF signal.
The converted 2nd IF signal is applied to the bandpass filter
(FI901) to suppress undesired signals.
The 455 kHz 2nd IF signal (except
WFM mode) is passed through the
bandpass filter (FI901) via the mode
switch (D803) and then amplified
at the IF amplifier (Q902). The
amplified signal is passed through
the bandpass filter (FI1001) and
then applied to another IF amplifier
(Q1001).
The amplified signal is applied to the 3rd mixer circuit.
The 10.7 MHz 2nd IF signal for WFM mode is passed
through the low-pass filter (L1402, C1402–C1404) via
the mode switch (D802) and then applied to the IF ampli-
fier (Q1401). The amplified signal is passed through the
bandpass filter (FI1401) and then applied another IF ampli-
fier (Q1402).
3 - 2
• 1st IF frequency
Mode 1st IF
USB 124.48850 MHz
LSB 124.48550 MHz
CW 124.48700 MHz
RTTY 124.48683 MHz
AM/FM 124.48700 MHz
WFM 134.73200 MHz
• 2nd IF frequency
Mode 2nd IF
USB 456.500 kHz
LSB 453.500 kHz
CW 455.000 kHz
RTTY 454.830 kHz
AM/FM 455.000 kHz
WFM 10.700 MHz