TM 1-1510-218-10 3B-5 (1)   Turn    On    Procedure.      Function   switch (UHF control panel)  – BOTH. (2)   Receiver Operating Procedure. 1.     Function switch – As required. 2.     Frequency – Select required frequency using either preset channel selector or manual frequency selector controls. NOTE The PRESET channel selector and manual frequency  selectors  are  inoperative  when the Mode Selector switch is set to GUARD. 3.   VOL – Adjust. 4.   SQUELCH – As required. (3)   Transmitter Operating Procedure. 1.   Transmitter  select  switch  located  on the audio control panel, Figure 3B -1  – UHF position. 2.   Microphone switch – Press. (4)   Shutdown Procedure.   Function switch  – OFF. d.    Emergency Operation. NOTE Transmission   on   emergency   frequencies (guard    channel)    shall    be    restricted    to emergencies only. An emergency frequency of 121.500 MHz is also available on the VHF command radio set. 1.   Transmitter  select  switch  located  on the audio control panel, Figure 3B -1  – UHF position. 2.   Mode selector switch – GUARD. 3.   Microphone switch – Press. 3B-8.  VHF COMMUNICATIONS     TRANSCEIVERS (VHF-22D). a.     Introduction.     The     VHF     communications transceivers  are  an  8.33  kHz  channel  spacing  cable system.  The  operation  between  the  25  kHz  and  8.33 kHz modes is seamless. Within the space occupied by each 25 kHz frequency exist three 8.33 kHz channels. The 8.33 kHz "frequency" is referred to as a "channel" not  the  actual  frequency  tuned.  The  channel  scheme avoids    possible    confusion    associated    with    shared 25 kHz    and    8.33    kHz    frequencies.    This    method ensures that the equipment will always be operating in the proper spacing mode and occurs automatically as the  user  tunes  the  controller.  Provides  airborne  VHF communications  from  118.000  through  151.975  MHz and  is  operated  by  two  CTL-22C  transceiver  control units.  Refer to Figure 3B -3. The    solid-state    transceiver    includes    capture- effect automatic squelch to help prevent missed radio calls,   plus   audio   leveling   and   response   shaping   to ensure   audio   quality.      Transmitter   sidetone   comes from   detected  transmitter  signal,  and  is  therefore  a reliable   check   of   transmission   quality.      Each   VHF transceiver  is  powered  through  its  respective  circuit breaker, placarded   VHF  1 or  VHF  2,  located  on  the circuit breaker panel. b.    VHF Transceiver Operating Controls (VHF-22C).  All operating controls for the transceivers are  located  on  the  CTL-22  transceiver  control  units.   Refer to Figure 3B-3. (1)   Active  Frequency  Display.    Displays  the active frequency (frequency to which the transceiver is tuned) and diagnostic messages. (2)   Transfer/Memory Switch. This switch is a three-position,  spring-loaded  toggle  switch  placarded XF/MEM, which, when held to the  XF position, causes the preset frequency to be transferred up to the active display   and   the   transceiver   to   be   returned.      The previously    active    frequency    will    become    the    new preset  frequency  and  will  be  displayed  in  the  lower window.  When this switch is held to the MEM position, one  of  the  six  stacked  memory  frequencies  will  be loaded into the preset display.  Successive pushes will cycle  the  six  memory  frequencies  through  the  display (...2, 3, 4, 5, 6, 1, 2, 3...). (3)   Store   Button.      This   button,   placarded STO,    allows    up    to    six    preset    frequencies    to    be selected  and  entered  into  the  control  unit's  memory.   After  presetting  the  frequency  to  be  stored,  push  the STO  button.    The  upper  window  displays  the  channel number  of  available  memory  (CHAN  1  through  CHAN 6)  while  the  lower  window  continues  to  display  the frequency to be stored.  For approximately 5 seconds, the  MEM switch may be used to advance through the channel numbers without changing the preset display.   Push the   STO  button  a  second  time  to  commit  the preset  frequency  to  memory  in  the  selected  location.   After  approximately  5  seconds,  the  control  will  return to normal operation.