TM 1-1510-225-10 3C-4 4.     AUDIO SPKR Switch – OFF. NOTE Headphone    audio    will    always    be    active regardless of SPKR / ON switch position. 5.     Move each audio panel select switch ON   then   OFF,   separately,   to   verify audio   output   from   headphones   for each system. 6.     Audio panel select switches  – Select switches ON as desired for communications. (3)   Transmit. NOTE When     selecting     the     desired     radio     for communications with the transmitter selector,    transmission    capability    only    is achieved. To receive, the associated audio panel select switch must be ON. 1.     Transmitter Select  –  As  desired  (HF, UHF, or VHF). 2.     MIC    NORMAL    /    OXYGEN    MASK Switch (instrument panel) – As desired. 3.     MIC Switch – Press to transmit. (4)   Intercommunication. 1.     Both AUDIO SPKR Switches – OFF. 2.     EMER    /    NORM    AUDIO   Switch    – NORMAL. Interphone communications are inhibited in EMER position. 3.     MIC    NORMAL    /    OXYGEN    MASK Switch (instrument panel) – As desired. 4.     INTPH  HOT  /  OFF  Select  Switch   – As desired. a.  INTPH HOT – Talk when ready. b.  INTPH – Rotate transmitter selector     to     INTPH,     press MIC switch, and transmit. 5.     VOL    Knob    (center    of    transmitter selector) – Adjust. (5)   Aircraft to Ground Intercom. A communications jack on the nose gear strut, placarded MIC  JACK,  is  provided  for  use  between  the  ground personnel and the pilot. The jack connects headphones and microphone to the aircraft interphone system   but   is   limited   to   use   between   the   ground personnel and the pilot position only.  When in use, the aircraft to ground system will inhibit inter- communications between the pilot and copilot regardless   of   the   transmitter   select   or   interphone switches  position.    The  aircraft  to  ground  interphone system   receives   electrical   power   through,   and   is protected    by,    the    circuit    breaker    placarded     NAV  MEMORY located on the hot battery bus. (6)   Cabin Intercom Operation. Rotate transmitter selector to  CABIN and press MIC switch to talk. (7)   Emergency   Audio   Operation.      Fail-safe emergency audio is available. If either amplifier for the dual  audio  panel  should  fail,  non-amplified signals will be directed to the headphones. NOTE An alternate method of activating emergency  audio  is  to  pull  both  the  pilot and copilot audio circuit breakers.  1.   EMER     /     NORM     Audio     Switch – EMER.      Both   systems   are   now   in emergency audio. 2.   VOL Controls (systems to be monitored) – Adjust. (8)   Shutdown. 1.     AVIONICS MASTER POWER Switch (pedestal) –  OFF. 2.     Avionics Controls and Circuit Breakers    –    Positioned    for    normal operation. 3.     Aircraft dc Power – OFF. 3C-7.  VHF COMMUNICATIONS TRANSCEIVER CTL-22. Refer  to  Chapter  3,  Paragraph  3-4  for  detailed information. 3C-8.  ULTRA-HIGH FREQUENCY. a.     Description.    The  UHF  (ARC-164) is a line of sight radio transceiver which provides transmission