NAVIGATION AND
COMMUNICATION
AIRPLANE
OPERATIONS
MANUAL
2-18-21
Page
12
Code
01
MARCH 30, 2001
3 - PROGRAM BUTTON
− Allows the user to store frequencies in the 40 user programmed
channels (refer to Programmable Channel Operation section for
proper operation).
4 - CHANNEL/FREQUENCY SWITCH
− The channel/frequency select knobs are used to select the
desired user channel or ITU telephone channel number
(CHAN/FREQ switch positioned to CHAN) or the proper transmit
and receive frequencies when operating in the discrete
frequency mode number (CHAN/FREQ switch positioned to
FREQ). The knobs are also used to enter frequencies when
programming the user channels number (CHAN/FREQ switch
positioned to CHAN).
5 - SQUELCH/TEST CONTROL
− This knob is adjusted to mute undesired background noise. The
noise proper setting is made by rotating the S (squelch) knob
clockwise from TST (test) position until background noise can
be heard and by turning it counterclockwise until the background
noise disappears or is just barely audible.
− When the S knob is in the TST position, the squelch circuit is, in
effect, removed from the receiver audio circuit in the TST,
maximum background noise (depending on the volume control
setting) will be heard.
− Setting the squelch control too far clockwise can result in
blocking out weak signals. There are times when it will be
necessary to leave the squelch control in the TST position to
maintain satisfactory reception. This is because of conditions
relating to propagation and the ionosphere that causes the HF
receiver to operate with a signal that is subject to considerable
fading and which is marginally strong.
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