TM 1-1510-223-10 4-2           Change 3 (11) Radio  altimeter  switch.  The  radio  altimeter switch, placarded RADIO ALT - ON, OFF, controls opera- tion  of  the  radio  altimeter  system.  This  switch  allows turning  off  the  radio  altimeter  system  to  reduce  radio emissions from the aircraft. (12) TDOA (CHAALS) system switch. The time di- rection  of  arrival  (CHAALS)  switch,  placarded  TDOA SYSTEM  ON  -  OFF,  controls  operation  of  the  TDOA system. (13) TDOA (CHAALS) test switch. The time direc- tion of arrival (CHAALS) test switch, placarded TDOA BIT ON, is used to initiate the TDOA built in test (BIT). (14) Data  link  high  voltage  switch.  The  data  link high  voltage  switch,  placarded  DATA  LINK  HV,  ON  - STBY - OFF, controls high voltage to the data link power amplifier. (a)   ON.    Applies  high  voltage  power  to  the data link power amplifier. (b)   STBY.  The STBY (standby) position ap- plies high voltage power to the data link power amplifier for warm up before ON is selected, and for cooldown before OFF is selected. (c)   OFF.  Removes high voltage power from the data link power amplifier. (15) Data link antenna select switch. The data link antenna select switch placarded DATA LINK ANT SEL - NOSE - AUTO - TAIL, is used to manually select the nose or tail data link antenna or to select automatic antenna selection. (16) Three-phase  AC  bus  cross  tie  switch.  The three-phase AC bus cross tie switch, placarded 3Ø AC CONTROL BUS CROSS TIE ON/AUTO - OFF, controls the AC bus cross tie. (a)   Due  to  the  additional  AC  loading  in  the RC-12N aircraft, a single three-phase inverter can no longer support all three-phase electrical loads. The au- tomatic bus cross-tying feature should only be used if the threat allows the mission to continue without use of the ALQ-136 radar jammer and the ALQ-162 CW jammer. If the threat dictates constant protection of the ALQ-136 and ALQ-162, the automatic bus cross tie feature for the three-phase  busses  should  not  be  used.  Cross  tying should  only  be  implemented  after  the  GRCS  mission equipment is shut off. (b)   OFF.  In the OFF position the AC busses will not be connected (no cross-tie). (17) Three-phase  AC  inverter  control  switches. Two three-phase AC inverter control switches, placarded 3Ø AC CONTROL #1 and #2 INV RESET - ON - OFF, control operation of the three-phase inverters. (a)   RESET.  When an inverter is off-line due either to a fault or to placing the inverter switch to the OFF position, the affected unit cannot have its output restored until the inverter switch is moved to the spring loaded RESET position, then to the ON position. (b)   ON.  ON position selects inverter opera- tion. (c)   OFF.  OFF position turns off inverter. (18) Three-phase AC external power switch. The three-phase AC external power switch, placarded 3ØAC CONTROL  EXT  PWR  -  RESET  -  ON  -  OFF,  controls application of external three-phase AC power to the air- craft. (a)   RESET.    The  AC  external  power  switch must be moved to the spring loaded RESET position, then to the ON position to bring AC external power on line. (b)   ON.  ON position applies AC external pow- er to the three-phase busses through the AC external power receptacle under the left wing. (c)   OFF.  OFF position removes AC external power from the three-phase busses. (19) Three-phase   AC   meter   switch.   The   three phase meters switch, placarded METERS AØ - BØ - CØ controls which phase of the three-phase inverters is be- ing measured by the AC voltage, frequency, and loadme- ters. (20) ASE control switch. The ASE control switch, placarded ASE SILENT - NORM - OFF, controls opera- tion of the ASE. (a)   SILENT.  When the SILENT position is se- lected, the transmitting elements of the ASE are placed in a passive mode. (b)   NORM.  The NORM position allows nor- mal ASE operation. (c)   OFF.    The  OFF  position  removes  power from ASE equipment. When the ASE control switch is set  back  to  NORM,  the  originally  selected  mode  will again become active.