TM 55-1510-220-10 (b) ADF.        Permits    automatic    direction finding or homing operation. (c) ANT.      Permits   reception   using   sense antenna. (d) LOOP.  Permits audio-null homing and manual direction finding operations. (8) GAIN  control.    Adjusts  volume  of  received signal. c. Controls    and    Functions    (Marker    Beacon    Audio Control Panel, fig.  3-2). (1) Receiver  audio  switch  (audio  control  panel) NAV B position applies ADF audio to respective headset. (2) FILTER V-OFF switch. Selects whether voice filter will be used with ADF audio. (3) FILTER    R-OFF    switch.        Selects    whether range filter will be used with ADF audio. NOTE Range and voice filtering are canceled when both FILTER R and FILTER V are  ON.    Range  and  voice  audio  will be heard. d. ADF Normal Operation. NOTE The only indication that the crewmember   has   for   an   unreliable ADF    signal    or    loss    of    the    ADF receiver  is  the  loss  of  the  ADF  audio signal in the crewmembers headset. (1) To operate the set as ADF. 1. Mode selector ADF. 2. BFO-OFF switch BFO. 3. Range switch Select frequency range. 4. Audio control panel (fig..  3-1) NAV B switch On and adjusted. 5. Gain control As required. 6. TUNE   control   Rotate   for   maximum reading on tuning meter and zero BFO beat. 7. BFO-OFF switch OFF. 8. Double needle switch (RMI, fig.  3-10) ADF. 9. Double needle pointer (RMI, fig.  310) Read course to station. (2) To  operate  set  for  sense  antenna  receiving only. 1. Mode selector (ADF control panel, fig. 16) ANT. 2. Range switch Select operating range. 3. Tune   control   Rotate   for   maximum   I reading on tuning meter. 4. Gain control As required. (a) To  operate  set  for  aural-null  direction finding. 1. Mode selector (ADF control panel, fig. 3-17) ANT. 2. BFO-OFF switch BFO. 3. Range switch Select operating range. 4. Tune control Tune desired station. 5. Gain control Adjust for minimum audio output. 6. Double needle switches (RMI, fig. 10) As required. 7. BFO-OFF switch OFF. 8. Mode selector switch LOOP. 9. Loop switch L or R.  Turn left or right until a null is reached (minimum sound in headsets). 10. Double needle on RMI (fig.  3-10) Read course to station. NOTE The   true   null   and   direction   to   the radio   station   may   be   indicated   by either  end  of  the  single  needle.    This ambiguity must be solved to determine proper direction to the station. (3) Shutdown procedure: Change 2 3-33