An inductively coupled sensing circuit for use on a common cable communications system is disclosed. When used in conjunction with transceivers on a common cable system, the circuit is capable of both detecting signals and determining the direction of any colliding signals while the transceiver is operating....http://www.google.com.au/patents/US4411004?utm_source=gb-gplus-sharePatent US4411004 - Inductively coupled sensing circuit and priority system
