FM radio broadcasting system with transmitter identification by means of a transmitted subcarrier whose frequency is a harmonic of subharmonic of the stereo pilot and which is binary phase modulated with transmitter identification signals. In the transmitter the subcarrier is locked to the stereo pilot...http://www.google.de/patents/US4252995?utm_source=gb-gplus-sharePatent US4252995 - Radio broadcasting system with transmitter identification
