TM 1-1510-224-10 (6) LX/I (green).    Indicates  that  the  receiver  is inhibited  by  the  XMIT  INH  input  during  transmission  by communications    transmitters.        No    lightning    may    be received during this condition. (7) LH/H  (green).    Indicates  that  heading  input has been deselected by the HDG VALID input. (8) LX/C (green).    Indicates  that  the  system  is in   the   self-calibration   mode.      This   will   revert   to   the selected mode approximately 10 seconds after power has been applied. (9) LX/L   (green).      The   number   of   computed lightning   rate   symbols   exceeds   the   capability   of   the display system. (10) LX (green).    Indicates  that  the  system  is  in the normal operating mode. NOTE If two or more of the above situations are    true    at    the    same    time,    the annunciation  which  is  highest  on  the above list will be displayed. NOTE:        EACH    RATE    SYMBOL    REPRESENTS    THE CENTER   OF   AN   18-MILE   DIAMETER   AREA OF LIGHTNING ACTIVITY. AP015461 C Figure 3-33.  Lightning Rate of Occurrence Symbols e. Self Calibration Mode. During approximately  the  first  8  seconds  after  power  is  applied, the  system  performs  a  self-calibration  process  to  cancel out variations in antenna gain and cable loss (LX/C will be displayed on the EHSI).  As soon as this is complete, the letter   C   will   be   removed   from   the   display.      If   strong interfering    signals    outside    the    aircraft,    or    equipment malfunction  prevent  the  calibration  of  the  system,  it  will revert  to  preset  calibration  factors,  in  which  case  the   C will  not  be  removed  from  the  display.    In  this  case  the operator  should  select  the   TST  mode   and   evaluate   the test display.  Interference signals can be caused by other systems  on  the  aircraft,  by  adjacent  ground  installations such   as   power   transformers,   or   by   nearby   aircraft.      If sources   outside   the   aircraft   cause   the    C    to    remain displayed,  they  will  not  be  present  after  takeoff,  and  the LSS mode selector switch should be switched to  OFF and set  back  to  the  LX  mode  to  force  recalibration  for  greater accuracy.    If  the   C  display  persists  after  takeoff,    TST mode should be selected again to re-evaluate the system. f. Self-Test. 1. Range  switches  (radar  control  panel, fig.  3-29)  Select  range  of  50  nautical miles or greater. 2. Lightning  sensor  system  (LSS)  mode selector  switch  (radar  control  panel) CLR/TST.      Verify   that   all   lightning rate symbols are erased from display. NOTE After    3    or    4    seconds,    simulated lightning  test  pulses  are  sent  to  the display. 3. Verify  that  a  rate  symbol  is  displayed at 25 nautical miles, at 45 degrees to right  of  center.    This  symbol  will  take approximately 5 to 7 seconds to build up. NOTE This time will be extended to approximately   15   seconds   if   TST   is selected  immediately  from  OFF,  due to lightning processor initialization. The  symbol's  range  may  vary  by  as  much  as  5 nautical    miles    if    strong    local    interference    is present. 4. Verify  that  a  magenta  lightning  alert symbol    is    displayed    at    maximum selected range, at 45 degrees right of center.    This  must  remain  on  display for 3 to 7 seconds. 5. To restart the test, switch to  LX mode and back to CLR/TST mode. 3-86