signals, or the two warning beeps. The microprocessor
then waits until the push-to-talk switch opens to sound
the two beeps.
To transmit for more than 2 minutes, release the
microphone switch briefly and then press it again. The
2-minute timer resets and starts a new count each time
the microphone switch is pressed.
Over-temperature protection. The
microprocessor regularly monitors the temperature of the
transmitter. If the transmitter gets too hot during a
transmission, and the sidetone will cease. When the
microphone switch is released, you will hear two beeps.
(Press the TEST switch on the transceiver control unit to
observe the fault code.) As long as the temperature
remains above the limit, the microprocessor will not
respond to a normal push of the microphone switch. If
you must transmit, however, you can override the
protection by rapidly keying the microphone switch twice,
temperature is 160°C (320°F).
Self-test. An extensive self-test
diagnostic routine can be initiated in the transceiver by
pushing the TEST switch on the transceiver control unit.
The control unit will modulate the active and preset
annunciate that self-test is in progress. Several audio
tones will be heard from the audio system while the self-
test routine is being executed. At the completion of the
self-test program, the transceiver control unit will usually
display dashes in the active display, and 00 in the preset
display. This indicates normal operation. If any out-of-
limit condition is found, the transceiver control unit will
display DIAG (diagnostic) in the active display and a 2-
digit fault code in the preset display. Record any fault
codes displayed to help the service technician locate the
problem. Refer to table 3-1 for a description of the self-
test fault codes that can be displayed on the transceiver
control unit. (The TEST switch must be pushed before
any fault code can be displayed.)
3-11. HF COMMUNICATIONS TRANSCEIVER (KHF-
Description. The HF communications
communications within the frequency range of 2.0000 to
29.9999 MHz (280,000 possible frequencies). The unit
can employ either amplitude modulation (AM) or upper
sideband (USB) modulation. (Lower sideband (LSB)
modulation has not been enabled in this installation.)
The HF system consists of a control display unit located
on the pedestal extension, a receiver/exciter, a power
antenna. The system is powered through a 25-ampere
5-ampere circuit breaker placarded HF RCV, located on
the overhead circuit breaker panel (fig. 2-9).
Controls and Functions.
Digital display. The digital display
information. The upper area of the display shows a two
digit channel number when in the program mode,
followed by a dash and the first one or two digits of the
operating frequency (with the emission mode selector
switch set to the USB or AM position). Transmitter
operation (TX) is shown at the right end of this display.
The lower line of the display shows the last four digits of
the operating frequency (with the emission mode
selector switch set to the USB or AM position).
Light sensor. A light sensor located
to the right of the display senses ambient light conditions
and adjusts display brightness accordingly.
Store switch. A momentary push
button switch placarded STO, is used to store in memory
the displayed data when programming preset channels.
When the STO switch is pressed simultaneously with a
attention tone will be transmitted (required by some
Canadian radiotelephone stations).
Frequency/channel selector knob.
The frequency/channel selector knob (inner concentric
with the emission mode selector switch) allows the pilot
to set channels and frequencies, and serves as a
clarifier control in sideband mode. Depressing the
control knob causes the flashing cursor on the display to
move to the digit that the pilot desires to change. Each
time the control is depressed, the cursor moves forward
to the next digit. The digit at the cursor position is
changed by rotating the channel/ frequency selector
Emission mode selector switch.
The emission mode switch, placarded LSB, USB, AM,
and TEL (A3J). (concentric with the frequency/selector
knob) is used to select the operating mode of the HF
Squelch control. A knob placarded
SQ (outer concentric with the off/volume control knob)
provides a variable squelch threshold control. This
control is used to help reduce background noise when a
signal is not being received.
(7) On, off, volume control. A knob placarded OFF, VOL
(inner concentric with the squelch knob) is used to turn
Clockwise rotation from the detent applies power to the