TM 55-1510-215-10
(9) STO (store) recessed switch.
Stores
There are three ways to set up a channel: Receive
displayed data when programming preset channels.
only, simplex, and semi-duplex. To gain access to
channelized operation, depress FREQ/CHAN button. To
(10) OFF-VOLUME . Applies power to the unit
utilize the existing programmed channels (i.e.
no
and controls the audio output level.
programming required) use the small control knob to
select the desired channel number. Then momentarily
(11) SQUELCH.
Provides variable squelch
key the microphone to tune the antenna coupler. If
threshold control. Squelch is set by rotating the knob
channel programming is required, it is necessary to
clockwise until background noise is heard then
activate the program mode as follows.
With the
counterclockwise until the noise is just barely audible or
FREQ/CHAN button in (CHAN), use a pencil or other
absent. Squelch operation on HF is not as predictable
pointed object to push the PGM button in. The button is
as is VHF.
Readjustment may be required more
an alternate action switch: push-on, push-off. The letters
frequent.
PGM will appear in the lower part of the display window
and the system will remain in the program mode until the
(12) CLARIFIER. Provides 250 Hz of local
PGM button is pressed again.
oscillator adjustment, thus providing better SSB
reception when a ground station is slightly off frequency.
(a) Receive only.
When receiving an unclear transmission, pull out the
knob and rotate in either direction to give a natural voice
1. Stow the cursor if a frequency digit
quality. Then push the knob in, the clarifier control
is flashing.
should be left in the inner position.
2. Select the channel to be pres et.
3. Set the desired operating mode
c. Methods of Operation (Frequency Selection).
(LSB,USB,or AM).
The HF system has two methods of operation The first
4. Set the desired frequency (refer to
method is called direct tuning (frequency agile). The
direct tuning).
second method is a channelized operation in which
5. Push and release STO button once.
desired operating frequencies are preset, stored and
referenced to a channel number.
NOTE
(1) Direct tuning (simplex only). Each digit of
T will flash in the display window,
the frequency may be selected instead of dialing up or
however a receive only frequency is
down to a frequency. The larger concentric knob is used
being set. The flashing T should be
to select the digit to be changed. This digit will flash
ignored.
when selected. Rotation of the knob moves the flashing
cursor in the direction of rotation. After the digit to be
NOTE
changed is flashing, the smaller concentric knob is used
to select the numeral desired. This process is repeated
If another channel is to be set, the
until the new frequency has been selected. The flashing
cursor must be stowed before a new
cursor may then be stowed by moving it to the extreme
channel can be selected. Use the
left or right of the display and then one more click. This
smaller concentric knob to select the
stows the cursor behind the display until needed again.
channel and repeat the steps for
The cursor may be recalled by turning the concentric
selecting a new frequency.
knob one click left or right.
6. To return to an operating mode,
(2) Channel programming. The long distance
push the PGM button.
propagation of HF signals depends on such factors as
atmospheric conditions, conditions in the ionosphere, the
(b) Simplex. Setting a channel up for
time of day, and the frequency being used. Therefore,
simplex operation (receive and transmit on the same
whenever possible, the 99 preset channels should be
frequency).
chosen so that communications with each of several
stations along the route is possible on three or more
1. FREQ/CHAN button in (cursor
frequencies spaced out well across the HF band. Then
stowed).
if there is some difficulty in communicating with a station
2. PGM button in (PGM displayed).
on one frequency, other frequencies that station is
3. Select channel to be preset.
guarding may be tried without having to set up a
frequency digit by digit.
3-10 Change 5
