TM 1-1510-224-10 f. Maritime Radiotelephone Network Channel Operation.    The  memory  of  the  control-display unit  has  all  176  ITU  (International  Telecommunications Union)   public   correspondence   channels   programmed permanently  into  its  memory.    Operation  in  this  mode  is as follows: 1. Emission mode selector switch - A3J. 2. Frequency/channel selector switch - Depress  repeatedly  until  channel  number is flashing. 3. Frequency/channel  selector  switch  -  Turn to select desired channel number. 4. Frequency/channel selector switch - Depress  repeatedly  until  cursor  is  at  digit to be changed. 5. Frequency/channel  selector  switch  -  Turn knob    until    desired    number    has    been selected. NOTE There  are  only  two  cursor  positions for   the   ITU   channel   number.      The hundreds  position  also  controls  the thousands  position.    For  example,  if the    displayed    channel    number    is 1204,  the  cursor  could  be  moved  to the  12  but  not  the  1.    With  the  cursor in the 12 position, turning the frequency/channel  selector  one  step counter-clockwise  will  change  the  12 to   an   8,   while   another   step   in   the same  direction  will  change  8  to  a  6. This   is   consistent   with   the   actual channel numbers. 6. Antenna   coupler   -   Tune   by   keying   radio momentarily.        During    antenna    coupler tuning   process,   TX   on   display   will   flash and frequency.  numbers -will be blank. 7. When  TX  annunciator  stops  flashing  and frequency reappears, antenna tuning cycle is complete and transceiver is ready to transmit on selected frequency. NOTE Always    key    the    microphone    after selecting  a  new  frequency  to  initiate antenna    tuning.        Otherwise    poor reception  or  failure  to  hear  a  ground station  which  is  calling  you  may  be experienced. Before keying the microphone to talk, depress the store (STO) switch momentarily. This will allow monitoring  of  the  transmit  frequency to see if another aircraft is calling the same ground station. Some  Canadian  public  correspondence  stations  require the reception of a 1,000 Hz signal from an aircraft calling the station before it will answer.  This signal may be sent by  keying  the  radio  and  then  simultaneously  depressing the store (STO) switch. 3-12.        VHF-FM    TRANSCEIVER    (AN/ARC-201A(V), SINCGARS). a. Description.      The   single   channel   ground and    airborne    radio    system    (SINCGARS,    AN/ARC- 201A(V))  provides  VHF-FM  radio  communications.    The frequency   range   is   30   to   87.975   MHz.      The   system provides  for  secure  communications  through  interfacing with a voice security system.  The system is protected by a  10-ampere  circuit  breaker  placarded  FM,  located  on the overhead circuit breaker panel (fig.  2-9). Control  of  the  VHF-FM  transceiver  is  provided by   the   aircraft   survivability   equipment/avionics   control system (ASE/ACS). b. Normal Operation. NOTE Some     operations     in     the     VHF-FM transceiver   require   several   seconds to accomplish. While these operations   are   active,   the   TUNING legend  (multifunction  display,  fig.    4- 2),  will  be  displayed  and  some  bezel buttons    will    become    inactive    until tuning is complete. (1) Turn-on procedure. 1. BATTERY switch (overhead control panel, fig.  2-15) -  ON. 2. AVIONICS MASTER POWER switch (overhead control panel, fig.  2-15) - ON. 3. Transmitter-intercom selector switch (audio control panel, fig.  3-1) - 2. 4. FM/AM  alternate  communication  selector switch (pedestal extension, fig.  2-14) - As required. 5. D    mode    selector    switch    (multifunction display,   fig.      4-2)   -   Depress   to   select COMM control page. 3-15