Icom IC-251A Instruction Manual page 26

For normal SSB reception, set the AGC switch in the AGC (up) position. Set the AGC switch
in the FAST (down) position, when tuning or receiving signals with short interval fading.
When in the FAST position, the time constant is shortened.
TRANSMITTING
Before transmitting, listen in the receive mode to maakes sure your transmission will not interfere
with other communications. If possible, use a dummy load for adjustment instead of an
antenna. Set the MIC GAIN CONTROL to the CENTER (12 o'clock) position.
Other knobs and switches are left in the same positions as for receiving. When the T/R switch
is moved to transmit, or when the PTT (push to talk) switch on the microphone is depressed,
the transmit LED is illuminated. By speaking into the microphone, the meter needle will
move according to the strength of your voice and SSB signals will be transmitted.
Hold the microphone about three inches from your mouth and speak in a normal voice. The
microphone is of the dynamic type and provides good pickup for all levels of voice.
To receive again, turn the T/R switch to RECEIVE or release the PTT button. This will also
switch OFF the transmit indicator.
HOW TO USE THE VOX CIRCUIT
The IC-251A/E has a built-in VOX (voice operated relay) which allows automatic T/R switch-
ing by voice signals into the microphone. For VOX use, set the knobs inside the top access
cover as follows:
VOX GAIN CONTROL Fully Counterclockwise
VOX DELAY CONTROL Fully Clockwise
ANTI VOX CONTROL Fully Counterclockwise
Turn the VOX switch on the front panel to the ON (down) position. Leaving the T/R switch
in the receive position and without pushing the PTT switch, turn the VOX gain control
clockwise while speaking into the microphone. At a certain point, the T/R switching circuit
will be activated by your voice. This is the proper position for the VOX gain control. See the
VOX Gain control at a level which provides for T/R switching at your normal voice level.
Transmit-release time (the time delay before the set automatically returns to receive when you
stop talking) is controlled by the VOX delay control. Turning the control counterclockwise
makes the time shorter. Set it at a position which is comfortable and which allows for short
pauses in normal speech.
Adjust the ANT! VOX control so that the VOX circuit is not activated by sounds from the
speaker by turning the control clockwise while receiving a signal.
CW OPERATION
1.
RECEIVING
For CW reception, set the MODE Select Switch to the CW position. Other switches and knobs
are set the same as for SSB reception.
Rotate the tuning knob until an 800Hz (approx.) beat tone is heard from the speaker or head
phones. Set the noise blanker switch and/or the AGC switch for clear reception, the same as
for SSB reception.