1. Transmitter Selector Switch
2. VOL Control
3. ICS # 2 OFF Switches
4. FILTER Switches
5. AUDIO NORM / EMER Switch
6. AUDIO SPKR / PHONE Switch
Figure 3A-2. Copilot's Audio Control Panel
(1) Turn-On Procedure. The audio control
panel is on whenever electrical power is applied to the
aircraft and the AVIONICS MASTER switch is ON.
(2) Interphone Operating Procedure.
1. Transmitter selector switch INTPH.
2. Microphone switch Press, listen for
3. VOL control Adjust sidetone and
interphone audio level in headphone.
(3) Navigational Aid And Receiver Monitoring
1. ICS # 1 or ICS # 2 switch As
2. VOL control Adjust volume control
of system being monitored.
(4) Transmitting Procedure.
1. Transmitter Selector Switch As
2. Microphone Switch Press, listen for
3. Applicable transceiver volume control
Adjust for comfortable audio level.
Operation. An audio fail-safe system is provided for
use in the event of an audio amplifier failure. If an
audio amplifier fails, receiver audio bypasses the
amplifier and is applied directly to the headsets and no
audio will be available to the overhead speakers.
3A-7. UHF COMMAND SET (AN/ ARC-164).
a. Description. The UHF command set
provides two-way Amplitude Modulated (AM) voice
communication within the frequency range of 225.000
to 399.975 MHz for a distance range of approximately
50 miles line-of-sight. Channel selection is spaced at
0.025 MHz intervals. Additionally, a separate receiver
is incorporated to provide monitoring capability for the
UHF guard frequency (243.0 MHz). The audio output
of the UHF set is applied to the audio control panel
where it is made available to the headsets and
speakers. The UHF command set is protected by the
5-ampere UHF circuit breaker on the overhead circuit
breaker panel. Refer to Figure 2-16, Sheets 1 and 2.
Figure 3A-3 illustrates the UHF command set. The
associated blade type antenna is shown in Figure 2-1.
b. Controls and Functions.
(Hundreds). Selects hundreds digit of frequency
(either 2 or 3) in MHz.
(Tens). Selects tenths digit of frequency (0 through 9)
(Units). Selects unit digit of frequency (0 through 9) in
(Tenths). Selects tenths digit of frequency (0 through
9) in MHz.
(6) Preset Channel Selector Switch. Selects
one of 20 preset channels.
(Hundreds and Thousands). Selects hundredths and
thousandths digits of frequency (00, 25, 50, or 75) in