Airborne Transponder Equipment Air traffic control radar beacon system
a light aircraft transponder the transponder has small required set of controls , simple operate. has method enter four-digit transponder code, known beacon code or squawk code, , control transmit ident, done @ controller s request (see spi pulse below). transponders typically have 4 operating modes: off, standby, on (mode-a), , alt (mode-c). on , alt mode differ in on mode inhibits transmitting altitude information. standby mode allows unit remain powered , warmed inhibits replies, since radar used searching aircraft , exact location of aircraft.