Beechcraft C-12C Operator And Technical Reference Manual page 296

TM 1-1510-218-10
1. Active Frequency Display
2. Transfer/Memory Switch
3. Store Button
4. Frequency Select Knobs
5. Active Button
6. Test Button
7. Light Sensor
8. Volume Control
9. Power and Mode Switch
10. Annunciators (MEM TX)
11. Preset Frequency Display
12. Compare Annunciator
Figure 3B-3. VHF Communications Transceiver
Control Unit
(4) Frequency Select Knobs. Two concentric
tuning knobs control the preset or active frequency
displays. The larger knob changes the three digits to
the left of the decimal point in 1-MHz steps.
smaller knob changes the three digits to the right of
the decimal point. The faster the kHz knob is turned,
the more channels will be skipped. A single click of
the kHz knob will either increase or decrease the
channel by a single channel.
(5) Active Button.
placarded ACT, enables the tuning knobs to directly
tune the VHF transceiver, when pressed and held for 2
seconds. The bottom window will display dashes and
the upper window will continue to display the active
frequency. Pushing the ACT button a second time will
return the control unit to the normal two-display mode.
(6) TEST Button.
TEST, initiates the transceiver self-test diagnostic
routine. Self-test is active only when the TEST button
is pressed.
(7) Light Sensor.
automatically controls display brightness.
3B-6
The
The active button,
This button, placarded
This built-in light sensor
(8) Volume Control. The volume control is
concentric with the power and mode switch.
(9) Power and Mode Switch. The power and
mode switch contains three detented positions. The
ON and OFF positions switch system power. The SQ
OFF position disables the receiver squelch circuits.
(10) Annunciators.
unit contains a MEM (memory) and a TX (transmit)
annunciator. The MEM annunciator illuminates
whenever a preset frequency is being displayed in the
lower window. The TX annunciator illuminates
whenever the transceiver is transmitting.
(11) Preset Frequency Display. Displays the
pre-set (inactive) frequency and diagnostic messages
in the lower window.
(12) Compare Annunciator. An annunciator,
placarded ACT, momentarily
frequencies are being changed. The ACT annunciator
flashes if the actual radio frequency to which the
transceiver is tuned is not identical to the frequency
shown in the active frequency display.
If two communications transceivers in the
same aircraft are tuned to stations carrying
the same voice message, attempting to
listen to the received signals from both
simultaneously could result in a great
reduction in the actual audio volume.
c. Operating Procedures.
capable CTL-22C shows the VHF COM frequency as
a channel frequency using all six digits of the display.
There are no 8.33 kHz channels above 136.992 MHz.
The last "channel name" is 136.990, which is an actual
frequency of 136.9917 MHz. Table 3B-1 shows the
channel/frequency scheme for the 180.000 to 136.992
MHz range. While the CTL is in the frequency range
of 137.000 to 151.975 MHz, the unit behaves the
same as a 25 kHz only unit.
It is possible that erroneous operation
could occur without a fault indication. It is
the responsibility of the pilot to detect
such an occurrence
assessing the reasonableness of operation
as displayed on the associated transceiver
control unit and by the quality of received
signals and transmissions.
The transceiver control
illuminates
NOTE
The 8.33 kHz
NOTE
by continually
when