TM 1-1510-218-10 3A-4 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 d.  Operation. (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 sidetone. 3.   VOL   control   –   Adjust   sidetone   and interphone audio level in headphone. (3)   Navigational Aid And Receiver Monitoring Procedure. 1.   ICS   #   1   or   ICS   #   2   switch   –   As required. 2.   VOL  control   –  Adjust  volume  control of system being monitored. (4)   Transmitting Procedure. 1.   Transmitter    Selector    Switch    –    As required. 2.   Microphone Switch  – Press, listen for sidetone. 3.   Applicable  transceiver  volume  control – Adjust for comfortable audio level. e.   Audio Control Panel Emergency 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.  (1)   Manual Frequency Selector Switch (Hundreds).        Selects   hundreds   digit   of   frequency (either 2 or 3) in MHz. (2)   Manual Frequency Selector Switch (Tens).  Selects tenths digit of frequency (0 through 9) in MHz. (3)   Manual Frequency Selector Switch (Units).  Selects unit digit of frequency (0 through 9) in MHz. (4)   CHAN Indicator. Displays preset channels. (5)   Manual Frequency Selector Switch (Tenths).  Selects tenths digit of frequency (0 through 9) in MHz. (6)   Preset Channel Selector Switch.   Selects one of 20 preset channels. (7)   Manual Frequency Selector Switch (Hundreds and Thousands).   Selects hundredths and thousandths digits of frequency (00, 25, 50, or 75) in MHz.