TM 55-1510-220-10 right  corner.    The  operating  mode  selected  by  the  MODE switches, either MAP, WX, or WXA, will be displayed in the lower left corner.  If WXA has been selected, the red band in the  test  pattern  will  flash  on  and  off.    The  range  will  be displayed  in  the  upper  right  corner  beneath  the  word  TEST and  appropriate  range  mark  distances  will  appear  along  the right edge of the screen.) (4) Weather observation operating procedure: 1. Function switch ON. 2. MODE  switches  Press  and  release  as required to select WX. 3. BRT control As required. 4. TILT    control    Adjust    until    weather pattern  is  displayed.    Include  the  areas above and below the rainfall areas to obtain a complete display. 5. MODE  switches  Press  and  release  to select  WXA.    Areas  of  intense  rainfall will appear as flashing red. These areas must be avoided. 6. TRACK  switches  Press  to  move  track line    through    area    of    least    weather intensity.      Read   relative   position   in degrees in upper left corner of screen. NOTE Refer to FM 1-30 for weather observation, interpretation and application. (5) Ground mapping operating procedure: 1. Function switch ON. 2. MODE  switches  Press  and  release  as required to select MAP. 3. BRT control As required. 4. GAIN  control  As  required  to  present usable display. (6) Standby procedure: Function switch STBY. (7) Shutdown procedure: Function switch OFF. (8) Weather    radar    emergency    operation.    Not applicable. 3-31.   TRANSPONDER SET (APX-100). a. Description.        The    transponder    system    receives, decodes,   and   responds   to   interrogations   from   Air   Traffic Control  (ATC)  radar  to  allow  aircraft  identification,  altitude reporting,  position  tracking,  and  emergency  tracking.    The system receives a radar frequency of 1030 MHz and transmits preset coded reply pulses on a radar frequency of 1090 MHz at  a  minimum  peak  power  of  200  watts.    The  range  of  the system is limited to line-of-sight. The   transponder   system   consists   of   a   combined receiver/transmitter/  control  panel  (fig.    327)  located  on  the pedestal  extension;  a  pair  of  remote  switches,  one  on  each control  wheel;  and  two  antennas,  located  on  the  underside and  top  of  the  fuselage.    The  system  is  protected  by  the  3- ampere    TRANSPONDER    and    the    35-ampere    AVIOICS MASTER PWR No.1 circuit breakers on the overhead circuit breaker panel (fig.  2-27). b. Controls/Indicators and Functions. (1) TEST-GO  indicator.    Illuminates  to  indicate successful completion of built-in-test (BIT). (2) TEST-MON indicator.  Illuminates to indicate system malfunction or interrogation by a ground station. (3) ANT   switch.        Selects   desired   antenna   for signal input. (a) TOP.  Selects upper antenna. (b) DIV.  Selects diverse (both) antennas. (c) BOT.  Selects lower antenna. (4) RAD   TEST-OUT   switch.      Enables   reply   to TEST mode interrogations from test set. (5) MASTER CONTROL. Selects system operating mode. (a) OFF.  Deactivates system. (b) STBY.          Activates    system    warm-up (standby) mode. 3-80