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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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