A multi-address two-way communication system with a control channel. A master position is inter-connected with a plurality of remote positions only over the AC power lines serviced by the same AC power distribution network. The master position contains a source of RF signals, an RF signal modulator and circuitry for energizing the RF signal source and the RF signal modulator to provide a very large number of unique signal combinations. Each remote position contains a decoder circuit which identifies and responds to a signal combination unique to it. A multiplicity of AC power lines in an AC power distribution network are coupled together by frequency selective coupling devices to permit signalling and communication between positions in separated AC power lines in a large building.