TM 55-1510-219-10 (3)    Test procedure. 1. Function switch TEST. 2. RANGE   switches   Press   and release  as  required  to  obtain 80 mile display. 3. BRT control As required. 4. Screen  Verify  proper  display. (The  test  display  consists  of two  green  bands,  two  yellow bands,  and  a  red  band  on  a 120-degree  scan.    The  word TEST will be displayed in the upper     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.) (a) 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   TM   1-230   for   weather observation, interpretation and application. (b) 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. (4) Standby    procedure.        Function    switch STBY. d. Shutdown procedure: Function switch OFF. e. Emergency operation.  Not applicable. 3-30.  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.  3-25) 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  AVIONICS  MASTER  PWR  #1  circuit  breakers on the overhead circuit breaker panel (fig.  2-26). b. Transponder Control Panel fig.  3-25). CONTROL FUNCTION TEST/GO Illuminates to indicate successful indicator completion of built-in-test (BIT). TEST/MON Illuminates  to indicate system indicator malfunction or interrogation by a ground station. ANT switch Selects desired antenna for signal input. TOP Selects upper antenna. DIV Selects diverse (both) antennas. BOT Selects lower antenna. RAD TEST Enables reply to TEST mode in- OUT switch terrogations from test set. 3-74