An extension telephone system communicates with a conventional subscriber telephone line where the subscriber's line telephone is located, through available AC power wires which carry signals that may be modulations of RF carrier frequencies and which are coupled to the power wires. Incoming telephone...http://www.google.fr/patents/US3949172?utm_source=gb-gplus-shareBrevet US3949172 - Telephone extension system utilizing power line carrier signals
Telephone extension system utilizing power line carrier signals
