(4.)  Transmitter  operating  procedure  (CI- PHER): 1.   Transmitter-interphone selector (audio  control  panel,  fig.  3-1)  - No.2  position. The  HF  system  has  two  methods  of  frequency selection.  The  first  method  is  called  direct  tuning (frequency  agile).  The  second  is  a  channelized  opera- tion in which desired operating frequencies are pre- set, stored and referenced to a channel number. 2. Plain-cipher  switch  (voice  security panel)  -  CIPHER.  (Indicator  will be illuminated while switch is in CIPHER position.) b.   Controls/Indicators   and   Functions   (HF Control Panel, jig. 3-7. (1.) selected. FREQ  display.  Displays   frequency 3.  RE-X-REG  switch  (voice  security panel) -  As  required.  (Set  RE-X position only if distant station is using  re-transmitting  equipment.) 4.   Microphone switch  - Press momentarily   (interrupted   tone from  voice  security  unit  should no longer be heard.) (2.) LSB,  AM,  or (3.) selected. MODE  display. Displays   selected USB mode. CHANNEL display. Displays channel (4.) Light  sensor.  The  light  sensor  is  a photocell which adjust brigntness of the display. NOTE (5.) MODE  switch.  The mode switch is a momentary  pushbutton  switch  that  selects  LSB,  AM or USB. No  traffic  will  be  passed  if  the  interrupted tone  is  still  heard  after  pressing  and (6.)   FREQ/CHAN   switch.   Transfers  the releasing  the  microphone  switch. HF  system  from  a  direct  frequency  operation  to  a channelized form of operation. 5. Microphone switch - Press (do not talk).  Wait  until  beep  is  heard, then speak into microphone. (7.)  PGM  (Program)  recessed  switch. Enables channelized data to be modified. The PGM message  will  be  displayed  whenever  this  switch  is depressed. (5.)  Shutdown  procedure: 1. Mode  selector  switch  (VHF AM-FM panel) - OFF. 2.   Power   switch   (voice   security panel) - OFF. NOTE 3-14.  HF  COMMUNICATION  SET  (KHF-950). a. Description. The HF command set (fig. 3-7) provides  long-range  voice  communications  within the  frequency  range  of  2.0  to  29.99  MHz  and employs  either  standard  amplitude  modulation (AM),   lower   sideband   (LSB),   or   upper   sideband (USB) modulation. The distance range of the set is approximately  2,500  miles  and  varies  with  atmo- spheric conditions. With the capability to preset and store 99 frequencies for selection during flight, the system also allows for selection of other frequencies manually (direct tuning), or reprogramming of any preset   frequency.   The   system   will   automatically match  the  antenna  by  keying  the  microphone.  Power to the system is routed through a 25 ampere circuit breaker  placarded  HF  PWR.  The  receiving  portion of  the  system  is  protected  by  a  5  ampere  circuit breaker  placarded  HF  REC.  Both  circuit  breakers are  located  on  the  overhead  circuit  breaker  panel. The program mode must be used for set- ting or changing any of the 99 preset fre- quencies. Each of the 99 channels may be preset  to  receive  and  transmit  on  separate frequencies  (semi-duplex),  receive  only,  or transmit  and  receive  on  the  same  fre- quency   (simplex).   The   operating   mode (LSB,USB  or  AM)  must  be  the  same  for both receive and transmit and can also be preset. (8.)   Frequency/channel   selector.   This selector  consists  of  two  concentric  knobs  that  con- trol the channel and frequency digits, plus the lateral position of the cursor. (a.)  Frequency  control.  The  outer knob becomes a cursor (flashing digit) control with the FREQ/CHAN switch in the FREQ position. The flashing digit is then increased/decreased with the inner  knob. (b.) Channel control. The outer knob is  not  functional  when  the  FREQ/CHAN  switch  is in the CHAN position. The inner knob will provide TM  55-1510-221-10 3-15