Icom IC-720 Instruction Manual page 13

5-1 HOW TO TUNE
The following instructions are for tuning in any mode.
Please read carefully and understand fully before turning
the unit on. Proper tuning is necessary for optimum
operation.
5-1-1 TUNING KNOB
The transmit or receive frequency is displayed on 7 segment
Electroluminesent display down to 100Hz digits. With all
buttons in their normal (out) position, rotating the tuning
knob clockwise increases the frequency, while turning
counter-clockwise decrease the frequency in 100Hz steps.
(or 10Hz steps, it depends on Tuning Rate Select switch
position) The smaller vernier marks on the knob represent
10Hz and the larger marks represent 100Hz. One complete
rotation of the tuning knob results іп 10KHz, 1KHz
frequency increase or decrease. When you receive your set,
calibration of the tuning knob may be desirable, as the
large increments may not correspond exactly to a change of
1KHz displayed on the readout. Exact calibration is not
necessary as the displayed frequency will always be correct
but you may calibrate the scale on the tuning knob for use
as an analog type frequency display. To calibrate, set a
large increment on the tuning scale to line up with the
indicator arrow directly above the scale and then turn on
the power.
To calibrate the scale during operation, if desired, set the
frequency readout to 0.ОКН2, push the dial lock button,
then set the large increment on the tuning scale to line up
with the indicator arrow and then push the dial lock button
again.
The tuning knob scale may require recalibration if you:
1. Turn the knob while the frequency is locked by use of
the Dial Lock Button.
2. Turn the knob beyond the band edge.
On all but the 28MHz band, the displayed frequency will
not go beyond the highest band edge even by turning the
tuning knob clockwise, or beyond the lowest band edge by
turning the knob counter-clockwise. On the 28MHz band,
since this band width is much wider than the others, the
ІС-720 provides "automatic revert" over either MHz for
operating convenience. When the frequency display shows
29.999.9MHz and the tuning knob is turned clockwise, the
displayed frequency jumps down to 29.000.0MHz and
continues up from there. Likewise, by continuing to turn
counter-clockwise beyond the bottom edge of the band, the
frequency jumps up from 29.000.0MHz to 29.999.9MHz
and goes down from that point. The same holds true for
the 28MHz segment.
The displayed frequency shows the carrier frequency in the
USB, LSB, AM and CW modes, and the Mark frequency in
the RTTY mode.
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5-1-2 DIAL SELECT BUTTON
Pushing the Dial Select Button will change the basic tuning
rate of the set. In its normal out position the tuning rate is
100Hz. When pushed in the tuning rate becomes 10Hz.
The 10Hz may be read from the increments on the tuning
knob.
5-1-3 TUNING SPEED BUTTON
Pushing the Tuning Speed Button will illuminate the dial
fast LED and the tuning rate is changed to correspond to
1KHz steps. The last significant-digit on the display is
blanked. When the Tuning Speed Button is depressed again,
the dial fast display LED goes off and the tuning rate will
again correspond to 100Hz (10Hz) steps. This button will
allow you to guickly QSY over a great frequency range.
5-1-4 DIAL LOCK BUTTON
After the ІС-720 is set at a certain frequency for rag chew-
ing, mobile operaticn, etc., pushing the Dial Lock button
will illuminate the Dial Lock LED and the VFO is locked at
the displayed frequency, thus inactivating the operation of
the tuning knob. To change the frequency, the Dial Lock
must first be disengaged by pushing the dial lock button
again. The Dial Lock display LED will go off, and the
frequency will change with the direction of the tuning knob
rotation. Turning off the power will release the Dial Lock.
5-1-5 VFO SELECT SWITCH
The CPU in the ІС-720 contains two "VFO's" for both
receiving and transmitting. The VFO's are labeled "A"
VFO and "В" VFO and are selectable with the VFO Select
Switch. This dual VFO system gives the ІС-720 many very
convenient features. Please read this section very carefully
and perform the operation several times until you are com-
fortable with the system.
1. "А" VFO в for both transmitting (ham bands only) and
receiving and is selected by placing the VFO Select
switch in the "А" position. Тһе transmit and receive
frequency will be controlled by "А" VFO, displayed оп
the frequency readout, and stored in "А" memory.
2. "В" VFO is for both transmittin (ham bands only) and
receiving and is selected by placing the VFO Select
switch in the "В" position. The transmit and receive
frequency will be controlled by "В" VFO, displayed on
the frequency readout, and stored in "В" memory.
FOR EXAMPLE:
If the band switch is set to the 7MHz band, when the set is
turned on, 7.100.0 will be displayed on the readout.
This will occur whether the VFO switch is in either the "A"
or "В". Rotating the tuning knob clockwise will increase
the frequency іп 100Hz (10Hz) steps. Rotating the tuning
knob counter-clockwise will decrease the frequency in
100Н2 (10Н2) steps.
Switching from one VFO to the other VFO does not clear
the first VFO. The frequency is retained in the VFO's
memory.