Icom IC-701

When the speech processor circuit is used, the output signal
of IC5 is fed to the speech processor circuit through D22
and D13.
6-1-3 SPEECH PROCESSOR CIRCUIT
The speech processor circuit uses the pass band tuning
circuit. While transmitting with the processor ON, a DSB
signal output in the balanced modulator is passed through
D22 and D13, and applied to 1C3, where it is mixed with
the VXO output frequency of 19.7615MHz. It passes
through the crystal filter FL2 and becomes an SSB signal
of 10.750MHz. This signal is mixed with the VXO output
at IC4 again to become an SSB signal of 9.0115MHz,
amplified by Q11, and passed to IC1. O11 as well as O12
and D19 are in the compressor level detection circuit, and
the output for the compressor level indicator is obtained
from the source of Q11. IC1 is the limiting circuit, and it
clips signals above a fixed level, as shown in the figure on
page 23.
O4 is the drive level control circuit. By turning the COMP
(compressor) control, the bias voltage is changed and gain
is controlled. Some splatter is included in the signal which
has passed through the limiter circuit, but this is completely
removed by the crystal filter FL1, and the final signal is
a clean and powerful SSB signal.
In the CW and RTTY modes, the speech processor circuit
works the same as in the SSB mode, and the output power
is adjustable from O to about 100 Watts by turning the
COMP control knob.
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6-2-4 TRANSMIT MIXER CIRCUIT
The output from P1 of the “A” unit is passed to J1 on the
RF unit, and after passing through the T/R switching diode,
D4, it is applied to Q1, the attenuator of the drive level
control for each band. [Each band has its own drive level
control in the RF amplifier circuit. In order to conpensate
for this, the voltage fixed at R92 to R97 is applied to the
gate of Q1, and proper drive for each band is obtained.
The output is mixed with the VCO output frequency in the
Schottky diode double balanced mixer circuit composed of
D5 to D8, and the output becomes the final transmitting
frequency. The mixed output is fed to RF amplifier
through the T/R relay RL1.
6-2-5 RF AMPLIFIER CIRCUIT
The mixed output is applied to the RF amplifier circuit
(the same one as is used in the receiver section) composed
of 015 to Q20 which are set for each band. L20 to L25
and L26 to L31 are multiple coupled resonant coils which
are staggered to obtain a flat wide band pass. The output
is fed through T/R switch diode D41, and is amplified by
Q9, the predrive circuit in the next stage, to a level of
about 50 milliwatts. This is then fed to J6.
6-2-6 TRANSVERTER OUTPUT CIRCUIT
When a transverter is used for VHF or UHF operation,
connect the input/output cable from the transverter to J4,
X-verter Jack on the rear panel. Also apply +8 Volts DC
to pin 11 of J1 (ACC socket) on the rear panel.
VHF/UHF
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