TM 1-1510-218-10 3A-10 (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 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  depressed  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. (9)   Power and Mode Switch.  The power and mode  switch  contains  three  detented  positions.    The ON and  OFF positions switch system power.  The  SQ OFF position disables the receiver squelch circuits. (10)   MEM  TX  Annunciators.    The  transceiver control unit contains a memory (MEM) and a transmit (TX)  annunciator.    The   MEM  annunciator  illuminates whenever a preset frequency is being displayed in the lower    window.        The    TX    annunciator    illuminates whenever the transceiver is transmitting. (11)   Preset  Frequency  Display.    Displays  the pre-set  (inactive)  frequency  and  diagnostic  messages in the lower window. (12)   Compare  Annunciator.    An  annunciator, placarded ACT, momentarily illuminates when frequencies are being changed.  The  ACT annunciator flashes   if   the   actual   radio   frequency   to   which   the transceiver  is  tuned  is  not  identical  to  the  frequency shown in the active frequency display. NOTE If  two  communications  transceivers  in  the same aircraft are tuned to stations carrying the   same   voice   message,   attempting   to listen   to   the   received   signals   from   both simultaneously    could    result    in    a    great reduction in the actual audio volume. c.   Operating    Procedures.         The    8.33    kHz capable  CTL -22C shows the  VHF  COM  frequency  as a channel frequency using all six digits of the display.   There are no 8.33 kHz channels above 136.992 MHz.   The last “channel name” is 136.990, which is an actual frequency  of  136.9917  MHz.    Table  3A-1  shows  the channel/frequency scheme for the 180.000 to 136.992 MHz    range.        While    the    CTL    is    in    the frequency  range  of  137.000  to  151.975  MHz,  the  unit behaves the same as a 25 kHz only unit. NOTE It   is   possible   that   erroneous   operation could occur without a fault indication.  It is the   responsibility   of   the   pilot   to   detect such an occurrence by continually assessing the reasonableness of operation as displayed on the associated transceiver control  unit  and  by  the  quality  of  received signals and transmissions.  (1)   Equipment Startup.    The  transceiver and the  control  unit  are  turned  on  by  rotating  the  power and mode switch on the transceiver control unit to the ON position.  When the transceiver is first turned on, it sounds  a  brief  tone  while  the  microprocessor  checks its own memory.  If there is a memory defect the tone continues,  indicating  that  the  transceiver  can  neither receive  nor  transmit.    After  the  memory  check,  the transceiver  control  unit  will  display  the  same  active and  preset  frequencies  that  were  present  when  the equipment was last turned off. If    two    short    800-Hz    tones    are    heard,    the transceiver  has  detected  an  internal  fault.    Push  the TEST button on the transceiver control unit to initiate self-test and display the fault code.