Table 3B-1. VHF Communications Transceiver Control UnitChannel/Frequency Scheme
(118.000 To 136.992 MHz Range)
transceiver and the control unit by rotating the power
and mode switch to the ON position. When the
transceiver is first turned on, it sounds a brief tone
while the microprocessor checks its own memory. If
there is a memory defect the tone continues, indicating
that the transceiver can neither receive nor transmit.
After the memory check, the transceiver control unit
will display the same active and preset frequencies
that were present when the equipment was last turned
If two short 800-Hz tones are heard, the
transceiver has detected an internal fault.
Push the TEST button on the transceiver
control unit to initiate self-test and display
the fault code.
Adjust the volume and perform a quick squelch
test by setting the power and mode switch to SQ OFF
and adjusting the volume level with background noise.
established, return the power and mode switch to the
ON position. All background noise should disappear
unless a station or aircraft is transmitting on the active
selection is made using either the frequency select
knobs, or the XF / MEM switch.
There is usually an installer supplied
8.33/25 kHz select switch in the cockpit.
This switch provides a convenience to the
pilots by not having to "ratchet pass" the
8.33 kHz channels when not operating in
8.33 airspace. The selected position of the
(8.33 or 25) switch may or may not be
annunciated, depending on installation.
After the desired frequency is set into the preset
frequency display, it can be transferred to the active
frequency display by momentarily setting the XF /
MEM switch to XF. At the same time that the preset
frequency is transferred to the active display, the
previously active frequency is transferred to the preset
display. A short audio tone is applied to the audio
system to indicate that the active frequency has been
changed, and the ACT annunciator will flash while the
transceiver is tuning to the new frequency.
The ACT annunciator continuing to flash
indicates that the transceiver is not tuned
to the frequency displayed in the active
The transceiver control unit's memory permits
storing up to six preset frequencies. Once stored,
these frequencies can be recalled to the preset display
by positioning the XF / MEM switch to the MEM
position. The storage location (CHAN 1 through
CHAN 6) for the recalled frequency is displayed in the