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IC1801 is a double balanced mixer IC and outputs a double
side band (DSB) signal with –40 dB of carrier suppression.
R1803 and R1807 adjust the balanced level of IC1801 for
maximum carrier suppression. The resulting signal passes
through a 9 MHz IF filter (FI1301 in SSB/CW/RTTY modes)
to suppress unwanted side-band signals.

In AM mode, R1811 is connected to upset the balance of
IC1801 via Q1803 for leaking the BFO signal as a carrier
signal. The CW keying/RTTY TX signal is applied to IC1801
pin 3.

3-2-4 FM MODULATION CIRCUIT (MAIN UNIT)

The microphone signals from Q1721 are applied to the IDC
amplifier (IC2201, pin 5). The sub-audible tone signal
(67.0–254.1 Hz) from the main CPU (IC5901, pin 2) is also
applied to the same amplifier (IC2201, pin 2) for repeater
use.

The resulting signals are applied to the VCO circuit (Q9621,
D9621) via IC2651 to change the reactance of the varactor
diode (D9622) for FM modulation. The modulated signal is
amplified at the buffer amplifier (Q9651).

3-2-5 TRANSMITTER IF CIRCUIT (MAIN UNIT)

The 9 MHz IF signal from the modulation circuit passes
through the 9 MHz IF filter (FI1301 in SSB/CW/RTTY
modes; FI1341 in AM/FM-N modes; through in FM mode).
The signal is amplified at Q1401, and then passes through
the crystal filter (FI1501). The signal is then applied to the
2nd mixer (D901).

The signal is mixed with the 2nd LO signal (60 MHz) and
converted to a 69 MHz IF signal at the 2nd mixer (D901).
The 69 MHz IF signal passes through a bandpass
filter(FI851), IF amplifier (Q831), and is then converted to
the displayed frequency at the 1st mixer (D701) with the 1st
LO signal. The mixers (D701) and bandpass filter (FI851)
are used commonly for both receiving and transmitting.

3-2-6 RF CIRCUIT (MAIN AND PA UNITS)

The RF circuit amplifies the displayed frequency signal to
obtain 10 W of RF output power for HF/50 MHz bands.

The HF/50 MHz RF signals from the 1st mixer (D701) via the
low-pass filter pass through one of 8 high-pass filters (Refer
to page 3-1 for used RF high-pass filter). The 50 MHz RF
signals pass through a low-pass filter additionally. The fil-
tered signals pass through the low-pass filter (except 50
MHz), are then amplified at the YGR amplifier (IC101) after
being passed through the high-pass filter to cut the unwant-
ed signal below 1.6 MHz, and are then applied to the PA
unit.

The signals from IC101 enter the PA unit and is amplified at
the pre drive and power amplifiers (Q101, Q150, Q200 and
Q201) to obtain a stable 10 W of RF output power in
sequence. The amplified signals are applied to the band
switch (RL250).

The power-amplified signals from the band switch (RL250)
are then applied to the [ANT] connector via one of the 7 low-
pass filters.

3-2-7 ALC CIRCUIT (PA AND MAIN UNITS)

The ALC (Automatic Level Control) circuit reduces the gain
of IF amplifiers in order for the transceiver to output a con-
stant RF power set by the RF power setting even when the
supplied voltage shifts, etc.

The HF/50 MHz RF power signal level is detected at the
power detector (D562, D563), buffer-amplified at IC560 and
applied to the MAIN unit as the “FORL” voltage.

The “FORL” voltage is applied to the ALC amplifier (MAIN
unit; IC2701, pin 2). The “POCV” voltage from the D/A con-
verter (MAIN unit; IC6501, pin 23), determined by the RF
power setting, is applied to the same amplifier (MAIN unit;
IC2701, pin 3) as the reference voltage.

2nd

mixer

1st

mixer

FM tone

D901

D701

Q9621
D9621

IC1621

IC2201

Crystal

filter