TM 1-1510-225-10 3-1 CHAPTER 3 AVIONICS (COMMON)   R  T3  F3 Section I.  GENERAL 3-1.  INTRODUCTION. This    chapter    covers    all    avionics    equipment common to the C-12R, C-12T3, and C-12F3 aircraft.  It provides   a   brief   description   of   the   equipment,   the technical   characteristics,   and   locations.      It   covers systems    and    controls,    and    provides    the    proper techniques   and   procedures   to   be   employed   when operating the equipment. For more detailed operational   information   consult   the   vendor   manuals that accompany the aircraft loose tools. 3-2.  AVIONICS EQUIPMENT CONFIGURATION. The  aircrafts’  common  avionics  consist  of  two groups  of  electronic  equipment.    The  communication group,    which    includes    the    HF    communication    set (KHF-950)  and  the  VHF  communications  transceivers (VHF-22D), and the transponder and radar group, that includes the APX-100 transponder. Section II.  COMMUNICATIONS 3-3.  HIGH    FREQUENCY    COMMUNICATION    SET (KHF-950). a.   Description.        The    KHF-950    HF    system consists  of  three  units:  the  panel  mounted  KCU  951 control display, the remote KAC 952 power amplifier/antenna coupler, and the KTR 953 receiver/exciter.    The  system  will  operate  on  any  0.1 kHz frequency between 2,000 and 29,999.9 kHz. With  the  capability  to  preset  99  frequencies  for selection   during   flight,   the   system   allows   for   either selection  of  other  frequencies  manually (direct tuning) or   reprogramming   of   any   preset   frequency.      The system will automatically match the antenna by keying the microphone. The  HF  system  has  two  methods  of  frequency selection.      The   first   method   is   called   direct   tuning (frequency    agile).        Th e   second   is   a   channelized operation  in  which  desired  operating  frequencies  are preset, stored and referenced to a channel number.    b.  HF   Control   Panel   and   Functions.       The operating  controls  of  the  HF  system  are  described  in the  following  paragraphs  and  are  illustrated  in  Figure 3-1. (1)   Frequency Display   –  Displays frequency selected. (2)   Mode   Display   –   Displays   LSB,   AM,   or USB indicating the mode. (3)   CHANNEL   Display   –   Displays  channel selected. (4)   Light Sensor   –   The  built-in  light  sensor automatically controls the display brightness. (5)   Emission  MODE Switch  –  The emission mode switch is a momentary push button that selects LSB, AM or USB. (6)   FREQ / CHAN Switch –  Transfers the HF system    from    a    direct    frequency    operation    to    a channelized form of operation. (7)   PGM Button  –  Enables channelized data to be modified.  The  PGM message will be displayed whenever  this  switch  is  pressed.    The  program  mode must  be  used  for  setting  or  changing  any  of  the  99 preset frequencies.  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  frequency  (simplex).    The  operating  mode, 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  control the   channel   and   frequency   digits,   plus   the   lateral position of the cursor. (a)  Frequency  Control.    The  outer  knob becomes   a   cursor   (flashing   light)   control   with   the FREQ   /   CHAN   switch   in   the   FREQ   position.      The flashing   digit   is   then   increased/decreased   with   the inner knob.