Icom IC-701

5-5-8 CONNECTION OF ACCESSORY SOCKET
Various adapters can be used through terminals in this
SOCKET for frequency control input, modulation output,
receiver output, T/R change-over control and so on. The
table below shows terminal connections of this connector.
Care should be taken not to apply voltages other than —0.5
V to +5V to terminals between No. 14 and No. 24 as they
are connected with the C-MOS IC.
OO OD®
ODD OO@
NC (no connection)
13.8 Volts DC in conjunction with the power
switch operation.
Connected to Push-to-talk, T/R change-over
switch. When grounded, the set operates in the
transmit mode.
Output from the receiver detector stage. Fixed
“output regardless of AF output or AF gain.
SECTION 6
“THEORY
ne Function
Output from Transmitter MIC amplifier stage.
8 Volts DC available when transmitting. (relay
can not be directly actuated.)
Input for external ALC voltage.
Ground
Input for RTTY keying (MARK: HIGH level,
SPACE: LOW level).
8 Volts DC available when the 28MHz band
is selected.
Input for TRANSVERTER control. When 8
Volts DC is applied, set can operate with a
transverter.
Output reference voltage for band switching.
INPUT/OUTPUT for external band switching.
CKE Output HIGH level at band edge.
LOCK Input to lock dial externally.
UDC Input to control Up/Down counter
externally.
SCAN Input to scan frequency.
CL Input to clear frequency.
FCL Input to clear counter in specified digit
and input for MSB data.
KO Input for frequency control data.
K1 Input for frequency control data.
K2 Input for frequency control data.
K4 Input for frequency control data.
K8 Input for frequency control data.
OUT LINE
The IC-701 employs a digital phase locked loop (PLL)
circuit as the local oscillator for both transmit and receive.
The output of the PLL circuit is approximately 9MHz
above the receive frequency, thereby spurious is kept to a
minimum.
The frequency is determined as follows. A pulse generated
by the optical chopper circuit, located at the tuning knob,
is digitalized by the up/down counter in the LSI (ICOM’s
custom developed Large Scale Integrated circuit) and used
to control a programmable divider, also located inside the
LSI chip. The programmable divider controls the PLL
circuit which determines the output frequency of the VCO
(Voltage Controlled Oscillator).
In the receiver section, signals from the antenna are mixed
with the local oscillator output from the PLL circuit.
After passing through the pass band tuning circuit, the
signals are amplified then detected to become audio signals,
amplified again and sent to the speaker.
The transmitter uses a carrier of 9.013MHz for USB and
9.010MHz for LSB. The carrier and the voice signal are
sent to a balanced modulator where the DSB suppressed
carrier signal is generated. The unwanted sideband is
removed by a crystal filter, and an SSB signal of 9.0115MHz
is obtained. This SSB signal is mixed with the local
oscillator output from the PLL circuit, which is the same
as that of the receiver section, and then amplified, filtered,
and sent to the antenna.
6-1 RECEIVER
6-1-1 RF AMPLIFIER AND MIXER CIRCUIT
A signal from the antenna is passed through the ALC and
filter units and applied to the antenna switching circuit
located on unit “B’’. During reception, Q17, the antenna
switching transistor, is ON, thus forward biasing D25 and
D26. The incomming signal passes through these diodes,
through the external receive antenna jumper, and is fed to
the attenuator circuit. If the attenuator switch on the
front panel is in the ON position, the signal passes through
the attenuator and is attenuated 10dB. The signal is then
fed to the RF unit through J3. If the attenuator switch Is
in the OFF position, the signal is fed directly to J3. D22
through D33 are switching diodes for the input and output
signals through their respective RF circuits depending on
the band selected. O15 through Q20 are dual gate MOS
FET amplifiers. The incomming signal is fed to the first
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