Icom IC-720A Instruction Manual page 21

5-4 RTTY OPERATION
For RTTY operation, a teletypewriter and a demodulator
(terminal unit) which is operational with audio input are
required. Any demodulator with 2125/2295Hz filters
(narrow, 170Hz shift) сап be used with the IC-720A.
5-4-1 RECEIVING
Audio signals for the demodulator can be supplied from Pin
4 of the ACC socket on the rear panel, or from the PHONES
jack on the front panel. The level of the audio signals from
Pin 4 of the ACC socket does not vary by turning the AF
GAIN Control, and the level is about 300mV P-P maximum.
Set the operating mode for RTTY, by pushing the MODE
SELECT switch "RTTY". The other controls are the same
as those for SSB reception. When tuning a RTTY signal, set
the TUNING RATE SELECT switch in the 10Hz position,
and tune to get audio signals of 2125Hz for MARK and
2295Hz for SPACE. (Use the tuning indicator of the
terminal unit for easy tuning.) Also turn the P.B. Tune
control for clear reception.
5-4-2 TRANSMITTING
For keying of the Frequency Shift Keying (FSK) circuit
insert а high speed геѓау"5 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. The
relay contacts make during the Space and break during the
Mark, as shown in the drawing. Fine adjustment of the
MARK and SPACE frequencies can be done by adjusting
the trimmer capacitors in the RTTY unit located next to
the internal fan accessible through the bottom cover.
When a high speed relay is used
(TU) SELECTOR
MAGNETS
KEYBOARD
LOOP CURRENT
POWER SUPPLY
When a level converter is used
(TU) SELECTOR
MAGNETS
KEYBOARD
LOOP CURRENT
POWER SUPPLY
LEVEL. CONVERTER
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