TM 55-1510-220-10 Section II.  COMMUNICATIONS 3-4.  DESCRIPTION. The   communications   equipment   group   consists   of   an interphone   system   connected   to   individual   audio   control panels  for  the  pilot  and  copilot  which  interface  with  VHF, UHF, HF, and SATCOM communication units. 3-5.  MICROPHONES, SWITCHES AND JACKS. Boom  and  oxygen  mask  microphones  can  be  utilized  in the aircraft. NOTE The audio system was designed for 5- OHM headsets. a. Microphone   Switches.      The   pilot   and   copilot   are provided    with    individual    microphone    control    switches, placarded  INTPH-XMIT-MIC,  attached  to  respective  control wheels.  A foot-actuated microphone switch is also positioned on the floorboards forward of each pilot's seat. b. Controls and Functions. (1) Microphone  control  wheel  switches  (fig.  2- 18).  Keys selected facility. (a) INTPH  (depressed  to  first  detent). Keys    interphone    facility,    disregards    position    transmitter selector switch. (b) XMIT  (depressed  full  down).  Keys facility selected by transmitter select switch. (2) Floorboard  microphone  switches  (fig.  2-7). Controls connection of selected microphone to audio system. (a) Held depressed.  Connects selected microphone to audio system. (b) Released.        Disconnects    selected microphone from audio system. c. Microphone   jack   selector   switches.      Two switches,  placarded  MIC  HEADSET-OXYGEN  MASK,  are located    on    the    extreme    left    and    extreme    right    of    the instrument panel (fig. 2-30).  These switches provide a means of   selecting   whether   the   headset   microphone   jack   or   the oxygen   mask   microphone   jack   is   connected   to   the   audio system. d. Controls and Functions. (1) MIC  HEADSET  -  OXYGEN  MASK  switch. Selects microphone jack to connect to audio system. (a)     MIC   HEADSET.      Connects   head-set microphone to audio system. (b) OXYGEN MASK. Connects microphone in oxygen mask to audio system. (2)     Communication radio monitor controls.  Each is  a  combination  rotary  volume  control  and  on-off  push-pull switch,    permitting    both    receiver    selection    and    volume adjustment. 3-6.  AUDIO CONTROL PANELS. a. Description.    Separate  but  identical  audio  control panels (fig. 3-1), serve the pilot and copilot.  The controls and switches  of  each  panel  provide  the  user  with  a  means  of selecting desired reception and transmission sources, and also a  means  to  control  the  volume  of  audio  signals  received  for interphone, communication and navigation systems.  The user selects  between  the  UHF,  VHF  and  HF  transceivers.    The audio  control  panels  are  protected  by  respective  2-ampere AUDIO   PILOT   and   AUDIO   COPILOT   circuit   breakers located on the overhead circuit breaker panel (fig.  2-27). b.  Controls and Functions. (1)     Master    VOL    control.        Controls    sidetone volume  to  headset.    Also  serves  as  final  volume  adjustment for   received   audio   from   any   source   before   admission   to headset. (2) Communication radio monitor controls.  Each is  combination  rotary  control  and  on-off  push-pull  switch, permitting both receiver selection and volume adjustment. (a) No.  1.    On  connects  user's  headset  to audio from VHF-AM transceiver No. 1. (b) No.  2.    On  connects  user's  headset  to audio from VHF/AM/FM and SATCOM transceivers. (c) No.  3.    On  connects  user's  headset  to audio from No. 1 UHF transceiver in use. (d) No.  4.    On  connects  user's  headset  to audio from HF transceiver. Change 2   3-2