A multiplexed audio-video signal transmission system has a camera-equipped intercom which produces a balanced audio-video signal. A twisted pair-wire connected to the intercom transmits a multiplexed signal of audio signal, video signal modulated to a frequency band not overlapping the audio signal frequency,...http://www.google.de/patents/US6014544?utm_source=gb-gplus-sharePatent US6014544 - Loop detector of a branching device for a multiplexed audio-video signal transmission system
