TM 55-1510-222-10
3-10. VHF
COMMUNICATIONS
TRANSCEIVERS
(VHF-22B).
a.
Description. VHF communications provide
transmission and reception of amplitude modulated
signals in the very high frequency range of 118. 000 to
151. 975 MHz for a range of approximately 50 miles,
varying with altitude. A dual head control panel (fig. 3-
3) is mounted in the pedestal extension, accessible to
both the pilot and copilot. The panel provides two sets
of control indicators, frequency indicators, frequency
select knobs, a single volume control, and a single
selector
switch
for
quick
frequency
changing.
Transmission audio is routed by pilot and copilot No.
transmitter selector switches located in the audio control
panel (fig. 3-1). Received audio is routed by pilot and
copilot No. 1 receiver audio switches (fig. 3-1), to the
respective headsets. The VHF radio is protected by the
10-ampere VHF circuit breaker in the overhead circuit
breaker panel (fig. 2-6). The associated antenna is
shown in figure 2-1.
b.
Controls/Indicators and Functions.
(1)
Frequency indicator. Displays the
frequency as selected by the frequency selector.
(2)
Control
frequency
indicators.
Indicates which frequency has been selected (left or
right) for use. Left or right selection is made with the
TRANS switch.
(3)
COMM TEST switch. The COMM
TEST switch when placed in the TEST position
overrides the automatic squelch circuit.
(4)
Frequency selectors. The frequency
selectors are used to select the desired operating
frequency. The selected frequency is indicated on the
frequency indicator.
(5)
TRANS
switch.
Selects
the
previously selected left or right frequencies for use.
(6)
VOL-OFF control. The VOL-OFF
control adjusts the volume of received audio, and turns
the set ON or OFF.
c.
VHF Set - Normal Operation.
(1)
Turn-on procedure: To turn the radio
on, turn the volume control clockwise out of the off
detent.
(2)
Operating procedure:
1.
Transmitter-interphone selector
switch (fig. 3-1) Select position desired, and turn the
respective radio monitor control to the ON position.
2.
Frequency selector Set desired
frequency.
3.
Volume control As required.
4.
Microphone switch Press to the
desired level to talk.
(3)
Shutdown procedure: Volume
control Turn counterclockwise, to the off detent.
d.
VHF Set Emergency Operation.
NOTE
Transmission
on
emergency
frequency (121. 500 MHz) is restricted
to emergencies only. Emergency
frequency 243. 000 MHz (guard
channel) is also available on the UHF
command radio.
1.
Transmitter-interphone selector
switch Select No. 1 position.
2.
Frequency selector 121. 500
MHz (emergency frequency).
3.
Microphone switch Press to
second level to talk.
3-11. HF COMMUNICATION SET (KHF-950).
a.
Description. The HF command set (fig. 3-
4) provides long-range voice communications within the
frequency range of 2. 0 to 29. 99 MHz and employs
either standard amplitude modulation (AM), lower
sideband (LSB), or upper sideband (USB) modulation.
The distance range of the set is approximately 2,500
miles and varies with atmospheric conditions. With the
capability to preset and store 99 frequencies for
selection during flight, the system also allows for
selection of other frequencies manually (direct tuning),
or reprogramming of any preset frequency. The system
will automatically match the antenna by keying the
microphone. Power to the system is routed through a
25-ampere circuit breaker placarded HF PWR. The
receiving portion of the system is protected by a 5-
ampere circuit breaker placarded HF RCVR. Both
circuit breakers are located in the overhead circuit
breaker panel. The HF system has two methods of
frequency
3-8
