TM 1-1510-225-10 3-4 controller.      Provides   airborne   VHF   communications from 118.000 through 151.975 MHz and is operated by two CTL-22D transceiver control units. The    solid-state    transceiver    includes    capture- effect automatic squelch to help prevent missed radio calls,   plus   audio   leveling   and   response   shaping   to insure 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-22D).   All operating controls for the transceivers are  located  on  the  CTL-22  transceiver  control  units.   Refer to Figure 3-2. (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 XFR  /  MEM,  which,  when  held  to  the   XFR  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. (4)   Frequency Select Knobs.  Two concentric tuning  knobs  control  the  preset  or  active  frequency displays.  The larger knob changes the three digits to the   left   of   the   decimal   point   in   1-MHz  steps.    The smaller  knob  changes  the  three  digits  to  the  right  of the  decimal   point.    The  knob  is  “Rate  Aided.”    The faster the kHz knob is turned, the more channels will be skipped.  A single click of the kHz knob will either increase or decrease the channel by a single channel. (5)   Active     Button. The active button, placarded  ACT,  enables  the  tuning  knobs  to  directly tune  the  VHF  transceiver,  when  pressed  and  held  for 2 seconds.    The  bottom  window  will  display  dashes and   the   upper   window   will   continue   to   display   the active  frequency.    Pushing  the   ACT  button  a  second time   will   return   the   control   unit   to   the   normal   two- display mode. (6)   Test    Button.        This    button,    placarded TEST,    initiates    the    transceiver    self-test    diagnostic routine.  Self-test is active only when the TEST button is pressed. (7)   Light  Sensor.      This   built-in  light  sensor automatically controls display brightness. (8)   Volume  Control.    The  volume  control  is concentric with the power and mode switch. 1.  Active Frequency Display 2.  Transfer/Memory Switch 3.  Store Button 4.  Frequency Select Knobs 5.  Active Button 6.  Test Button 7.  Light Sensor 8.  Volume Control 9.  Power and Mode Switch 10.   Annunciators (MEM   TX) 11.   Preset Frequency Display 12.   Compare Annunciator Figure 3-2.  VHF Communications Transceiver Control Unit