TM 1-1510-218-10 3B-23 (2)   Receiver Operating Procedure. 1.   Frequency   selector   –  Select  desired frequency   and   press   the   frequency transfer switch. 2.   NAV 1  or 2 switch (Figure 3B -1)  – As required. 3.   VOL control – As required. (3)   Shutdown Procedure. OFF / VOL control – OFF. 3B-22.  ADF RADIO SETS (KDF-806). a.     Description.        Two    ADF    radio    sets    are installed.      Refer   to   Figure   3B -14.      The   units   are airborne   low   frequency   radio   direction   finders   that receive    signals    from    transmitters    in    the    190    to 1750 kHz    range    to    provide    a    visual    and    aural indication  of  the  aircraft's  bearing  in  relation  to  the transmitter.  The set can also be used for homing and position  fixing.    The  KDF-806  has  a  Beat  Frequency Oscillator   (BFO)   function,   used   to   more   accurately tune   weak   signals.      Reception   distance   of   reliable signals     depends     on     the     power     output     of     the transmitting  station  and  the  atmospheric  conditions.   Bearing indications are displayed visually on the RMI's and   aural   signals   are   applied   to   the   audio   control panels.    The  system  is  protected  by  two  2-ampere circuit breakers, placarded  ADF 1 and  ADF 2, located on  the  overhead  circuit  breaker  panel,  Figure  2-16, Sheet 3. The  KDF-806  incorporates  a  KFS-586A control unit.    The  control  unit  contains  a  digital  display  that presents  both  the  active  and  standby  frequencies.  A photocell  automatically  adjusts  the  display  brightness according to changes in ambient light conditions.  The KFS-586A   switches/controls   provide   power   to   the receiver,   control   the   audio   output   level,   control   the OFF BFO  ADF, and ANT BFO modes of the receiver, maintain the active and standby frequencies, and tune the  receiver  to  the  active  frequency.    The  KFS-586A will retain the active and standby frequencies through a power off condition. b.    Controls and Functions. (1)   Control  Display.      Provides   a   display  of selected frequencies and bearing validity.  The display contains  two  frequencies  and  an  X  character.    The upper    frequency    is    the    active    frequency,    or    the frequency  to  which  the  receiver  is  tuned.    The  lower frequency   is   the   standby   frequency.      The   standby frequency is changed by the frequency select knobs in the  lower  right  corner  of  the  control  unit.    An  X  to  the right  of  the  active  frequency  informs  the  pilot  that  the bearing  indicator  (RMI)  directional  information  is  not valid. 1.     Control Display 2.     Light Sensor 3.     Frequency Transfer Switch 4.     Frequency Select Knobs 5.     Volume Control Knob 6.     OFF / ADF BFO / ANT BFO Function Control Knob Figure 3B-14.  ADF Control Unit (2)   Light  Sensor.    A  photocell  automatically adjusts the display brightness according to changes in ambient light conditions. (3)   Frequency  Transfer  Switch.    Provides  a means  of  interchanging  the  active/standby  displayed frequencies.    The  transfer  switch,  when  momentarily pressed, causes the active and standby frequencies to interchange.  When the transfer switch is pressed and held,  the  two  frequencies  interchange  on  the  display and    approximately    2    seconds    later    the    standby frequency will blank out.  Pressing the transfer switch momentarily again will cause the standby frequency to reappear. (4)   Frequency   Select   Knobs.      Provides   a means  of  selecting  frequencies.    The  normal  method of  selecting  a  frequency  is  with  both  the  active  and standby  frequencies  showing.    The  frequency  select knobs will then tune the standby frequency; however, the active frequency may be changed by  pressing and holding the frequency transfer switch for approximately 2  seconds.    The  standby  frequency  display  will  blank out.  The active frequency display may then be directly tuned by rotating the frequency select knobs.