Icom IC-751A Instruction Manual

3)
Tune in an RTTY
signal
using
the
tuning
indicator
of the
terminal
unit or
the
cross pattern
of
an
oscilloscope
to center
the receiver
on the signal. Mark
frequency
is 2125Hz
and
space frequency is
2295Hz.
Adjust the PBT
CONTROL
as required
for the
best reception.
4)
If an optional
narrow
CW filter
is installed,
push the FUNCTION
SWITCH, then the RTTY
SWITCH
to
select the
narrow
filter.
The receiver
selectivity
will
be
narrowed.
•
OPTIONAL FILTERS
FILTER
CENTER
FREQUENCY
CHARACTERISTICS
(BANDWIDTH)
-6dB
-60dB
FL-52A
455kHz
500Hz 1.0kHz
FL-53A
455kHz
250Hz
480Hz
5)
To
tune
RTTY signals with
a
wider shift,
such
as
425Hz
or
850Hz, obtain
a
demodulator suitable for the
desired shift and
use
the normal
RTTY mode.
(3)
RTTY
TRANSMITTING
1)
To key
the FSK circuit,
insert
a high
speed
relay
coil into the
loop
current circuit
of
the teletypewriter, and connect the
relay
contacts to
pins
8
and 9
of the
ACC
SOCKET
on the rear panel.
2)
The relay
contacts make
during the SPACE
and break during the
MARK.
3)
Fine
adjustment of the
MARK and SPACE frequencies
can be
made by adjusting the trimmer
capacitors in the MAIN
unit.
Refer
to
SECTION
13-4
ADJUSTMENT
LOCATIONS.
•
USING A
LEVEL
CONVERTER
1)
When a
level converter for TTL
levels
is used,
connect th6 output
of the
converter to
pin
8
(ground)
and pin 9
on the
ACC
SOCKET.
2)
Apply
HIGH
level (5V) signals for MARK, and LOW
level (OV)
for SPACE.
If your
equipment supplies
reverse polarity
signals (i.e., MARK:
OV,
SPACE:
5V), slide
S2
on the
MAIN unit
to the REVERSE
position.
See SECTION
13-4
ADJUSTMENT LOCATIONS for
the S2
location.
•
USING
AN AFSK
GENERATOR
1)
When using
an AFSK
generator with a
2125Hz
MARK
frequency
and
2295Hz SPACE
frequency, connect
the
output signals
from
the
AFSK
generator to
the MIC
CONNECTOR
on the
front
panel or ACC
socket on
the rear
panel.
2)
Push the LSB
SWITCH.
6-8
GENERAL
COVERAGE RECEIVER
3)
VOX T/R
switching may
be used
while
operating
AFSK for
easier
operation.
NOTE: -When in
the
GENERAL
COVERAGE
mode, it
is not
possible to
transmit
on
any
frequency,
including the
Amateur band
frequencies.
-
30
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Icom IC-751A Specifications

General

Brand	Icom
Model	IC-751A
Category	Transceiver
Language	English