TM 1-1510-218-10 3A-11 Table 3A-1.  VHF Communications Transceiver Control UnitChannel/Frequency Scheme (118.000 To 136.992 MHz Range)   FREQUENCY SPACING (kHz ) CHANNEL NAME (DISPLAYED) FREQUENCY SPACING (kHz ) CHANNEL NAME (DISPLAYED) 118.0000 25.00 118.000 118.0750 25.00 118.075 118.0000 8.33 118.005 118.0750 8.33 118.080 118.0083 8.33 118.010 118.0833 8.33 118.085 118.0167 8.33 118.015 118.0917 8.33 118.090 118.0250 25.00 118.025 118.1000 25.00 118.100 118.0250 8.33 118.030 118.0333 8.33 118.035 118.0417 8.33 118.040 118.0500 25.00 118.050 136.9750 25.00 136.975 118.0500 8.33 118.055 136.9750 8.33 136.980 118.0583 8.33 118.060 136.9833 8.33 136.985 118.0667 8.33 118.065 136.9917 8.33 136.990 Adjust  the  volume  and  perform  a  quick  squelch test  by  setting  the  power  and  mode  switch  on  the transceiver  control unit to   SQ  OFF  and  adjusting  the volume     level     with     background     noise.          After     a comfortable    listening    level    has    been    established, return the power and mode switch to the  ON position.   All    background    noise    should    disappear    unless    a station    or    aircraft    is    transmitting    on    the    active frequency. (2)   Frequency Selection. Frequency selection  is  made  using  either  the  frequency  select knobs, or the XF / MEM switch. NOTE There    is    usually    an    installer    supplied 8.33/25   kHz   select   switch   in   the   cockpit.   This  switch  provides a convenience to the pilots  by  not  having  to  "ratchet  pass"  the 8.33  kHz  channels  when  not  operating  in 8.33 airspace.  The selected position of the (8.33 or 25) may or may not be annunciated, depending on installation. After the desired frequency  is set into the preset frequency  display,  it  can  be  transferred  to  the  active frequency   display   by   momentarily   setting   the   XF  / MEM switch to  XF.  At the same time that the preset frequency   is   transferred   to   the   active   display,   the previously active frequency is transferred to the preset display.    A  short  audio  tone  is  applied  to  the  audio system to indicate that the active frequency has been changed, and the  ACT annunciator on the control will flash   while   the   transceiver   is   tuning   to   the   new frequency. NOTE The    active    annunciator's    continuing    to flash  indicates  that  the  transceiver  is  not tuned   to   the   frequency   displayed   in   the active display. The  transceiver  control  unit's  memory  permits storing  up  to  six  preset  frequencies.    Once  stored, these frequencies can be recalled to the preset display by   positioning   the   XF   /   MEM   switch   to   the   MEM  position.      The   storage   location   (CHAN   1   through CHAN 6) for the recalled frequency is displayed in the active frequency display while the  XF / MEM switch is held in the   MEM  position.    All  six  stored  frequencies can be displayed one at a time in the preset display by repeatedly   positioning   the   XF   /   MEM   switch   to   the MEM  position.  After the desired stored frequency has been    recalled    to    the    preset    display,    it    can    be transferred    to    the    active    display    by    momentarily positioning the XF / MEM switch to the XF position. During normal operation, all frequency selections and revisions are done in the preset frequency display.   However, the active frequency can be selected directly as described in the following paragraph.