TM 1-1510-218-10 3B-24 The outer control knob selects from 100 to 1700 kHz in increments of 100 kHz, then rolls over to 2182 kHz.  The smaller inner knob selects from 100 to 1799 kHz   in   increments   of   10   kHz   with   the   small   knob pushed in, and 1 kHz with the small knob pulled out.   Between  2180  and  2189  kHz  the   small  inner  knob selects the 1 kHz whether pushed in or pulled out. (5)   Volume Control Knob.  Adjusts volume of audio. (6)   OFF  /  ADF  BFO  /  ANT  BFO  Function Control  Switch.    Controls  operational  functions  of  the unit. (a)   OFF. Removes power from the unit. (b)   ADF BFO. Allows for audio identification of stations with unmodulated signals and selects  normal  operation.    The  needle  will  point  to  the station. (c)   ANT BFO. Allows for audio identification of stations with unmodulated signals and operates  as  aural  receiver  only.    Bearing  needle  will park in a horizontal position. c.    Operating Procedure. 1.   Control switch – Turn clockwise, out of OFF position. 2.   ADF 1 or  2 audio switch (Figure 3B-1) – ON. 3.   ADF BFO switch – As required. 4.   ANT BFO switch – As required. 5.   Volume control – Adjust as required. 3B-23.  TACAN/DME. a.    Description.    The  KTU-709 TACAN system consists    of    the    following    components:    KFS-579A NAV/TAC    control    unit    and    KDI-573B    DME    slave indicator. The  KTU-709  Tactical  Air  Navigation  (TACAN) system  is  a  polar  coordinate  UHF  navigation  system that provides relative bearing and slant-range distance information   with   respect   to   a   selected   TACAN   or VORTAC  ground  station.    The  effective  range  of  the TACAN is limited to the line-of-sight.  Actual operating range depends on the altitude of the aircraft, weather, type   of   terrain,   location   and   altitude   of   the   ground transmitter and transmitter power.  Usually line-of-sight limitations  will  prevent  an  aircraft  on  the  ground  from receiving   and   locking   on   to   a   TACAN   or   VORTAC ground station. The range measurement  portion  of  the  KTU-709 TACAN  system  electronically  converts  elapsed  time- to-station by measuring the length of time between the transmission of a radio signal to a preselected TACAN, or VORTAC station, and reception of the reply signal.   The distance is then indicated in nautical miles on the range/    groundspeed/time-to-station    indicator.        The distance is measured on a slant from the aircraft to the ground  and  is  commonly  referred  to  as  slant-range distance.          Slant-range     distance     should     not     be confused  with  actual  ground  distance.    The  difference between  slant-range  distance  and  ground  distance  is smallest at a low altitude and long range.  However, if the  range  is  three  times  the  altitude  or  greater,  the error  is  negligible.    To  obtain  accurate  groundspeed and  time-to-station,  the  aircraft  must  be  on  a  direct course   to   or   from   a   TACAN   or   VORTAC   ground station. The KTU -709 TACAN system provides an audio capability  allowing  the  pilot  to  identify  the  TACAN  or VORTAC ground station by listening to the identification tones transmitted by the ground station at 30-second  intervals.    It  also  features  an  in-flight  self- test mode for both bearing and range.  The system is protected   by   a  2 -ampere  circuit  breaker,  placarded TACAN,   located   on   the   overhead   circuit   breaker panel, Figure 2-16, Sheet 3. The KFS-579A  NAV/TAC  tunes  the  KTU -709 to 252  TACAN  channels.    Refer  to  Figure  3B-12.    Fifty- two  TACAN  channels  are  paired  with  frequencies  in the  COMM  band.    These  are  channels  1  through  16 and    60    through    69,    which    correspond    to    VHF frequencies 134.40 MHz through 135.95 MHz respectively.      Distance   and   bearing   information   is displayed  on  the  pilot's  #1  HSI.    Associating  the  #1 NAV    with    the    pilot's    #1    HSI    will    be    helpful    in maintaining a sequence of operation. The   KDI-573B   DME    slave    indicator    displays range to the nearest tenth of a nautical mile from 0 to 99.9  nautical  miles  and  to  the  nearest  nautical  mile from   100   to   389   nautical   miles.      Groundspeed   is displayed  to  the  nearest  knot  from  0  to  999  knots.   Time-to-station is displayed to the nearest minute from 0  to  99  minutes.    The  display  will  indicate  99  minutes for   any   computed   time-to-station    greater    than    99 minutes.    The  indicator  will  display  RNAV  when  the displayed range, groundspeed and time-to-station are derived from an area navigation system.  The indicator will display dashes while in search when power is first turned   on   or   momentarily   interrupted   while   in   the frequency   hold   mode   indicating   loss   of   the   DME holding  frequency.    A  photocell  automatically  adjusts