TM 1-1510-224-10 NOTE When     storing     a     frequency,     the     second actuation  of  the  STO  switch  must  be  done within  5  seconds  after  selecting  the  channel number   or   the   first   actuation   of   the   STO switch.    If  more  than  5  seconds  elapse,  the control   will   revert   to   the   normal   modes   of operation   and   the   second   store   command will be interpreted as the first store command. After a frequency has been stored in memory, it will remain there until changed by using the  STO switch. Memory  is  retained  even  when  the  unit  is  turned  off  for an extended period of time. d. Normal Operation. 1. Power    and    mode    switch    -    ANT, ADF, or TONE (BFO). 2. Tuning knobs - Set desired frequency. 3. ANT  function  -  Position  power  and mode  switch  to   ANT.    Select   ADF on audio system and adjust volume. 4. ADF function   -   Position   power   and mode    switch    to     ADF.        Bearing pointer  will  indicate  relative  bearing to tuned station. NOTE When   the   ADF   system   is   not   receiving   a reliable     signal,     bearing     pointer     will     be removed    from    view.        The    ADF    bearing pointer may momentarily blank during station crossings because of signal loss. 5. TONE function - Position power and mode   switch   to   TONE   (BFO).      A 1000-Hz tone will identify keyed CW stations. (1)   Self-test. 1. Power and mode switch - ADF. 2. Tuning knobs - Tune a nearby NDB, compass locator, or broadcast station. 3. TEST   switch   -   Depress.      Bearing pointer  will  rotate  90  degrees  from the previous valid indication. Release TEST switch and verify that the bearing pointer returns to previous valid indication. NOTE If   the   signal   received   is   weak   or   of   poor quality, bearing pointer rotation will be slow. ADF receiver fault codes are listed in table 3-8. 3-26.  TACAN/DME SYSTEM (AN/ARN-154). a. Description.    The  TACAN/DME  system  (fig. 3-26)          operates     in     conjunction     with     TACAN     and VORTAC ground stations to provide distance, groundspeed,   time   to   station,   and   bearing   to   station. The TACAN/DME system electronically converts elapsed time to distance by measuring the length of time between the transmission of a radio signal to a selected DME/TACAN   station   and   the   reception   of   the   reply signal.    The  distance  is  measured  on  a  slant  from  the aircraft to the ground station and is commonly referred to as    slant-range    distance.        Slant    range    approximates actual  ground  distance.    The  difference  between  slant- range  distance  and  ground  distance  is  smallest  at  low altitude   and   long   range,   and   greatest   when   in   close proximity  to  the  selected  ground  station.    The  system  is capable  of  tracking  the  range  of  up  to  four  stations  and the bearing of two stations simultaneously.  The system will  operate  on  any  one  of  252  preselected  frequencies (126   X   mode   and   126   Y   mode   channels).      Course deviation,  bearing  to  station,  and  distance  to  TACAN  or VORTAC stations are displayed on the EHSI.  Distance, time to station, bearing, Table 3-8.  ADF Receiver Fault Codes CODE INTERPRETATION 00 No faults 02 RAM test failed (test failed at power-up) 03 No serial sync block received 04 No serial data block received for more than 2 seconds 05 Transponder label received in first block 06 I/O port 1 failure 07 I/O port 2 failure 08 Illegal ADF frequency 09 Serial input failed or stuck low 10 ADF not lock in ADF mode BT03845 3-64