Icom IC-720 Instruction Manual page 17

5-3-3 CW SIDE-TONE (MONITOR)
When keying the side-tone oscillator is activated and a
800Hz tone wiil be heard. The loudness of the tone is
controlled by the CW Moni Control located under the top
access cover. Rotating the control clockwise will increase
the loudness. This tone is also audible in the receive mode
and can be used for code practice, adjustment of the keyer,
etc.
5-3-4 ЗЕМ! BREAK-IN OPERATION
The ІС-720 has Semi Break-In CW capability when using
the VOX function. When keying, the unit is automatically
set in the transmit mode. After keying, it is returned to the
receive mode, also automatically, after a given transmit-
release delay time constant. Leave the T/R switch in the
Receive position, and set the VOX switch in the on (IN)
position. 5
The transmit release delay time constant is set by adjusting
the CW DELAY Control located under the TOP access
cover. Turning the CW DELAY Control clockwise will
make the transmit release time longer. Set for your keying
speed.
5-4 RTTY OPERATION
For RTTY operation, а teletypewriter and а demodulator
(terminal unit) which is operational with audio input are
required. Any demodulator with 2125/2295MHz, narrow,
170Hz shift can be used. Filters can be used with the
IC-720. Fine adjustment of the MARK frequency can be
done by adjusting the variable capacitor located next to
the internal fan accessible through the bottom cover.
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.
Set the MODE Switch to RTTY. The frequencies for
NARROW shift are 2295MHz for SPACE and 2125Hz for
MARK.
If you һауе an AFSK generator, set the MODE Select
Switch on LSB for RTTY operation. Also turn the P.B.
Tune control fully clockwise for clear reception.
5-4-2 TRANSMITTING
For keying of the Frequency Shift Keying (FSK) circuit
insert a high speed relay's 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.
When a level converter for TTL level signals is used, connect
the output of the converter to Pins 8 (ground) and 9 of the
ACC Socket Apply High level (5V) signals for the Mark, and
Low (OV) for the Space. When using an AFSK generator
that has 2125Hz for Mark and 2295 for Space, connect the
output signals for the AFSK to the Mic connector on the
front panel and set the Mode to LSB. (See other operations
chapter.) Doing this, you can use the VOX operation
available in this mode, and receive/transmit changeover is
very easy.
When a high speed relay is used
ACC SOCKET AF
() (8) 69 (6) 69 @
000008
(2 (6 (9 69 (9 @
ВТТҮ
DEMODULATOR
(TU)
LOOP CURRENT
POWER SUPPLY
TTY
MACHINE
SELECTOR
MAGNETS
KEYBOARD
60mA or 20mA LOOP
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