A passive signal coupler transfers data signals being transmitted over AC power lines from a first AC power distribution system to a second AC power distribution system. Each leg of the passive signal coupler coupled to a phase of the power line voltage includes a series LC circuit, tuned to the data...http://www.google.com/patents/US4675648?utm_source=gb-gplus-sharePatent US4675648 - Passive signal coupler between power distribution systems for the transmission of data signals over the power lines
