TM 1-1510-225-10 3A-3 (2)   Transmitter Selector Switches. (a)   VHF  1 and  VHF  2  Position.    These positions   connect   the   user's   headset   or   speaker  to audio   from,   and   connect   user's   microphone   to   the respective VHF communications transceiver transmitter. (b)   AM  /  FM   Position.    These  positions connect  the  user’s  headset  or  speaker  to  audio  from and     connect     user’s     microphone     to     the     AM/FM (VHF/UHF) communications transceiver transmitter. (c)   HF.  This position connects the user's headset or speaker to audio from, and connects user's microphone    to    the    respective    HF    communications transceiver transmitter. (d)   CABIN     Position. This position connects user's microphone to the cabin speakers. (3)   Master    Volume    Control.        The    master volume    control,    placarded     VOL,    located    on    the transmitter selector switches, controls audio volume. (4)   Cockpit   Speaker   Switch.      This   switch, placarded   AUDIO   SPKR   OFF,   is   set   to   the   on   up position to route desired audio to the cockpit speakers. (5)   Audio Emergency/Normal Switch.  A two- position   switch   placarded    AUDIO    EMER   /   NORM, provides   a   means   of   selecting   a   secondary   audio source  in  the  event  of  a  failure  disabling  both  audio amplifiers.      When   the    switch   is   set   to   the   EMER position,  power  is  removed  from  both  audio  amplifiers and  audio  is  routed  directly  from  the  receivers  to  the headsets.    Speaker  audio  and  cabin  intercom  will  be inoperative.    When  the  switch  is  set  to  the   NORM position, audio is routed normally through an amplifier to speakers or headsets. (6)   Voice/Range    Switch.        The    pilot    and copilot  are  each  provided  with  a  three-position switch, placarded  VOICE  /  BOTH  /  RANGE,  which  controls selection  of  ADF  voice  or  range  filtering.    When  the switch is set to the  VOICE position, the range tone is disabled,   enhancing   voice   identification.      When   the switch   is   set   to   the   RANGE   position,   the   1020   Hz range tone is enhanced, and voice is suppressed. (7)   Paging    Volume    Control.        The    paging volume    control,    placarded    PAGING   VOL,    controls audio volume to the cabin speakers. (8)   Interphone Volume Control. The interphone   volume   control,   placarded   INTPH   VOL, controls interphone audio volume. (9)   Hot Interphone Switch. The hot interphone    switch,    placarded    HOT   INTPH   /   OFF, allows selection of interphone system. (10)   Sidetone  Volume  Adjustment  Port.    The pilot  and  copilot  are  each  provided  with  a  sidetone volume  adjustment  port,  placarded   SIDETONE,  that allows adjusting the volume level of the sidetone. (11)   Interphone   Sensitivity   Adjustment   Port.   The    pilot    and    copilot    are    each    provided    with    an interphone     sensitivity     adjustment     port,     placarded INTPH   SENS,   that   allows   adjustment   of   the   voice actuated interphone activation sensitivity level. (12)   DME    1    HOLD   Switch-Indicator.        The DME 1  HOLD function is controlled by a push on/push off switch indicator, placarded  DME 1 HOLD PUSH / SW.    Pressing  the  switch-indicator  selects  the   DME hold    function    and    causes    the    switch-indicator    to annunciate ON. (13)   TACAN    DME    1    Volume    Control.        A TACAN DME 1 volume control, placarded TAC DME 1 VOL, controls volume level of TACAN/DME 1 audio. (14)   Ground  Communication  Switch.    A push on/push off switch, placarded  GND COM PWR PUSH ON  /  OFF,  allows  selection  of  ground  comm  feature.   When   selected,   the   ground   comm   feature   applies power to the number 1 VHF communications transceiver allowing radio communication while on the ground without setting the  BATT switch or  AVIONICS MASTER PWR to on. (15)   Marker Beacon Sensitivity/Test Switch.  A three-position switch, placarded  MKR BCN 1 & 2  HI / LO  /  TEST,  selects  sensitivity  of  the  marker  beacon receivers and test function.  When the switch is set to the HI position, the marker beacon receivers are set to high  sensitivity.    When  the  switch  is  set  to  the    LO position,  the  marker  beacon  receivers  are  set  to  low sensitivity.      When   the   switch   is   held   in   the   spring- loaded TEST position, the marker beacon annunciator lights will be illuminated. (16)   Marker   Beacon   Volume   Control.       The marker beacon volume control, placarded  MKR BCN 1 & 2 VOL, allows adjustment  of  the  audio  volume  level of both marker beacon receivers. (17)   DME    2    HOLD   Switch-Indicator.       The DME 2 HOLD function is controlled by a push on/push off  switch-indicator, placarded   DME  2  HOLD  PUSH  / SW.    Pressing  the  switch-indicator  selects  the  DME hold    function    and    causes    the    switch-indicator    to annunciate ON.