Beechcraft C-12C Operator And Technical Reference Manual page 367

panel to the left of the tuning knobs is used to store in
memory the displayed data when programming preset
channels.
(8) OFF / VOLUME Control.
placarded OFF / VOLUME, located on the HF control
panel turns the system off and on and controls volume.
Clockwise rotation from the detent applies power to
the system. Further clockwise rotation increases
audio output level.
(9) SQUELCH Control.
SQUELCH on the HF control unit provides a variable
squelch threshold control.
(10) CLARIFIER Control. A knob placarded
CLARIFIER PULL ON located on the lower left corner
of the HF control unit is used to eliminate unnatural
audio quality when operating in the Single Sideband
(SSB) mode by slightly shifting the receiver generated
frequency to match the frequency of the signal being
received. To operate the clarifier, the knob is pulled
out and rotated in either direction from the index mark
(which is located directly above the clarifier knob) until
the audio quality is optimized. When the voice quality
is natural the clarifier knob should be pushed in.
Turning the clarifier knob has no effect when it is
pushed in.
c. Frequency Selection. The HF system has
two methods of frequency selection, frequency mode
and channel mode.
frequencies are tuned directly on the display using the
tuning knobs. In the channel mode, preset channels
are programmed with an assigned channel number (1
through 99) and stored in memory.
(1) Frequency Mode.
mode, the desired frequency is set into the display
using the tuning knobs.
allowed while operating in the frequency mode.
(2) Channel Mode. When the HF control unit
is in the channel mode, channels and their respective
frequencies are changed using the tuning knobs. To
place the unit into the channel mode, press the
FREQ/CHAN switch. This allows access to existing
programmed channels.
mode are stored with channel number, emission mode
(USB, LSB, or AM), and transmit and receive
frequency.
(3) Program Mode. When the HF control unit
is in the program mode, channel numbers, emission
mode (USB, LSB, or AM), and transmit and receive
frequency are set up and stored in memory.
program mode is entered from the channel mode by
pressing the PGM switch with a pencil or other pointed
A knob,
A knob placarded
In the frequency mode,
In the frequency
Only simplex operation is
Frequencies in the channel
object. When in the program mode, channel number,
emission mode, and transmit frequency are all
displayed. Transmitter operation is inhibited.
transmit frequency may be examined by keying the
microphone. Channels may be programmed for the
following types of operation.
(a) Receive
programs a frequency in the receive portion of transmit
frequency. The transmitter is locked out when a
channel has been programmed for receive only
operation. The receive-only function is used for
listening to weather, time, omega status, frequency
standard, and geophysical alert broadcasts.
(b) Simplex Operation.
programs the same frequency in receive and transmit,
and assigns an operating mode (USB, LSB, or AM).
The simplex function is used by air traffic control,
ARINC, and others.
(c) Semi-Duplex.
operation the
frequencies, one for transmit and one for receive.
The semi-duplex function is used by maritime
radio/telephone
stations.
d. HF
Operation.
(1) Direct
(Simplex Only).
(a) Frequency/Channel Switch – FREQ
(out position).
(b) Mode
emission mode (USB, LSB, or AM).
(c) Tuning
frequency, then stow cursor.
(d) Antenna Coupler – Tune, press
microphone button.
(2) Programming Preset Channels.
(a) Receive Only.
The
TM 1-1510-218-10
Only. The
In
operator programs
network (public correspondence)
Communications
Frequency Tuning
Selector Switch
Knobs –
1. Cursor – Stow if a frequency digit
is flashing.
2. Tuning Knobs – Select channel to
be preset and desired frequency.
The
operator
The operator
semi-duplex
two different
Transceiver
Operation
– Set
Set desired
3C-13