A method is provided for controlling transponder replies to Mode-S interrogation signals. The method includes receiving Mode-S signals containing P5 and P6 pulses each having certain amplitudes. Each P6 pulse contains a sync phase reversal (SPR) signal followed by a data segment containing Mode-S data....http://www.google.com/patents/US6788245?utm_source=gb-gplus-sharePatent US6788245 - Device and method for SPR detection in a mode-S transponder
