Icom IC-251A Instruction Manual page 11

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In addition, when the VFO is switched from "A" VFO to "B" VFO, the frequency indicated
on the frequency display just prior to switching goes into a memory inside the CPU chip.
Thus, even if "'B'' VFO is being used, switching to "A" again will enable you to operate at the
initial frequency. Switching from "'A" to "'B" results in the same operation.
RIT CONTROL
Shifts the receiver frequency +800Hz either side of the transmit frequency. When the RIT is
ON, the RIT LED is illuminated. The LED also represents the ''0' position. Rotating the
control to the (+) side raises the receiver frequency, and rotating to the (—) side lowers the
receiver frequency. With the RIT ON, if the Tuning Control Knob @ is moved one increment,
the RIT circuit is automatically pulsed OFF. Therefore it is not necessary to manually turn
OFF the RIT when changing operating frequency. The frequency shift by turning the RIT
Control is not indicated on the frequency display.
RIT SWITCH |
This is a spring-loaded switch for the RIT Control. To turn ON the RIT, push down once. If
the OFF position is desired, push down again. When the RIT is ON, the LED above the RIT
control knob is lit. This LED also indicates the center position of the RIT control. When the
RIT circuit is OFF, the LED is also OFF. Also, if the RIT is ON, rotating the Tuning Knob
by one increment will pulse the RIT OFF. The RIT remains ON even after the power is
turned OFF. ;
NOISE BLANKER SWITCH
When pulse-type noise such as automobile ignition noise is present, set this switch to the ON
(down) position. The noise will be reduced to provide comfortable reception.
AGC (AUTOMATIC GAIN CONTROL) SWITCH
With this switch you can select the time constant of the AGC circuit. With the switch in the
AGC (up) position, the AGC voltage is released slowly, and thus is suitable for SSB reception.
With the switch in the FAST (down) position, the AGC voltage is released faster, and the AGC
is suitable for stations suffering from fast fading or when operating in the CW mode.
TRANSMIT/RECEIVE (T/R) SWITCH
This switch is for manually switching from transmit to receive and vice versa. Set the switch
to RECEIVE (up) and the 1C-251A/E is in the receive mode. Set the switch to TRANSMIT
(down) and it switches to transmit. When switching with the PTT switch on the microphone
or with the VOX switch set to ON, the T/R switch must be in the RECEIVE position.
VOX SWITCH |
This switches the VOX circuit ON and OFF. When the switch is in the ON (down) position
in SSB, T/R switching is accomplished by means of a voice signal. In CW operation, semi-
break-in switching by means of keying is possible.
DIAL LOCK SWITCH
After the IC-251A/E is set to a certain frequency for rag chewing, mobile operation, etc., by
switching the DIAL LOCK Switch to the ON position (down), the VFO is electronically
locked at the displayed frequency, and this inactivates the operation of the Tuning Knob.
To change frequency, the Dial Lock must first be disengaged by setting the DIAL LOCK
Switch to OFF (up) position.