TM 1-1510-223-10 solid   state,   three   phase   inverters.      The   three   phase inverters  are  controlled  by  two  three-position  switches placarded 3Ø   AC CONTROL, #1 and #2 INV, RESET - ON - OFF, located on the mission control panel (fig. 4- 1). Section II.  COMMUNICATIONS 3-4. COMMUNICATIONS EQUIPMENT GROUP DESCRIPTION. The  communications  equipment  group  consists  of  an intercom  system  connected  to  individual  audio  control panels for the pilot and copilot which interface with VHF, UHF,   BU   VOW,   VHF-FM,   and   HF   transceivers,   and provide reception of audio from VOR, localizer, marker beacon, TACAN/DME, and ADF receivers. 3-5. MICROPHONES, SWITCHES, AND JACKS. Boom and oxygen mask microphones can be utilized in the aircraft a. Control    Wheel  Microphone  Switches.    The  pilot and  copilot  are  each  provided  with  bi-level  microphone switches placarded MIC, INTPH - XM1T, located behind the outboard handgrip of their respective control wheels (fig.    2-22).        When    the    control    wheel    microphone switches    are    depressed    to    the    first    level    (INTPH position),    voice    audio    signals    from    the    respective microphone   are   routed   to   the   intercom   system   (the position  of  the  transmitter-  intercom  selector  switch  is disregarded). When   the   control   wheel   microphone   switches   are depressed  to  the  second  level    (XMIT  position),  voice audio signals from the respective microphone are routed to  the  transmitter  selected  by  the  transmitter-intercom selector switch (located on the respective audio control panel, fig. 3-1). b. Cockpit Floor Foot-Operated Microphone Switches.  The pilot and copilot are each provided with a foot-operated microphone switch, placarded MIC, located  on  the  cockpit  floor,  forward  of  their  respective seat positions. Depressing   the   foot-operated   microphone   switches routes   audio   signals   to   the   device   selected   by   the transmitter-intercom    selector    switch    located    on    the respective audio control panel (fig. 3-1) c. Microphone Jack Selector Switches. Two switches, placarded MIC, HEADSET - OXYGEN MASK, located   on   the   left   and   right   sides   of   the   instrument panel  (fig.  2-16),  provide  a  means  of  selecting  which microphone   jack   is   connected   to   the   audio   system. When    the    pilot's    or    copilot's    switch    is    set    to    the HEADSET  position,  the  head-  set  jack  is  connected  to the respective audio system.  When set to the OXYGEN MASK  position,  the  oxygen  mask  jack  is  connected  to the respective audio system. 3-6. AUDIO CONTROL PANELS. a. Description.        Separate    identical    audio    control panels (fig. 3-1), located on the left and right subpanels (fig.  2-6),  are  provided  for  the  pilot  and  copilot.  Each audio   control   panel   is   powered   by   its   respective   2- ampere   circuit   breaker   placarded   AUDIO   PILOT   or AUDIO  COPI    located  on  the  overhead  circuit  breaker panel (fig. 2-7). b. VHF-FM/VHF-AM Alternate Communication Switch Panel.  An alternate communication switch panel with three alternate-action (push on, push off) switches, located   on   the   pedestal   extension   (fig.   3-2),   allows position 2 of the audio control panel transmitter-selector switch to be connected to an alternate transceiver. (1) VHF-FM/VHF-AM  alternate  communication selector  switch.  The  center  alternate-action  (push  on, push  off)  alternate  communication  switch  is  placarded FM,  AM.    When  the  switch  is  depressed,  either  FM  or AM will be illuminated.  When the switch is set to the FM position,  position  number  2  of  the  transmitter  selector switch (audio control panel, fig. 3-1) and number 2 radio monitor    control    will    be    connected    to    the    VHF-FM (SINCGARS)  transceiver  for  both  transmit  and  receive functions.  When  the  switch  is  set  to  the  AM  position, position   number   2   of   the   transmitter   selector   switch (audio  control  panel,  fig.  3-1)  and  the  number  2  radio monitor    control    will    be    connected    to    the    VHF-AM number   2   transceiver   for   both   transmit   and   receive functions. (2) Pilot's and copilot's alternate communication monitor switch.  The pilot and copilot are each provided with   an   alternate   action   (push   on,   pull   off)   alternate communication  monitor  switch,  located  on  the  left  side (pilot's   switch)   or   right   side   (copilot's   switch),   of   the alternate communication switch panel (pedestal extension,  fig.  2-12).    Both  switches  have  illuminated placarding  which  reads  MON,  ON  -  OFF.    When  the switch    is    depressed,    either    ON    or    OFF    will    be illuminated.    When  either  of  the  switches  is  set  to  ON and the center switch is set to FM, the VHF-AM number 2 audio will be heard in addition to the FM audio.  The FM audio cannot be monitored when the center switch is set  to  AM.    The  monitored  audio  volume  will  not  be controlled by the number two radio monitor control. 3-2