03949172 is referenced by 74 patents and cites 2 patents.

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 line signals are detected and modulate a first RF carrier frequency which is coupled to the AC power wires at the line telephone location and these signals are coupled from the AC power wires at an extension telephone location, and, demodulated and fed to an extension telephone which is energized by DC power derived from the AC power wires at the extension location. The extension telephone produces extension telephone signals which modulate a second RF carrier frequency which is coupled to the AC power wires at the extension location and this modulated carrier is coupled from the AC power wires and demodulated at the line telephone to produce the extension telephone signals in suitable form for applying to the telephone line. Thus, telephone calls to the subscriber's line telephone can be received by the extension telephone and calls to the telephone extension telephones can be connected to this system wherever there is access to the same AC power wires.

Telephone extension system utilizing power line carrier signals
Application Number
Publication Number
Application Date
February 8, 1974
Publication Date
April 6, 1976
Robert T Dunn
4 Cedar Ridge Drive, Bedford, 01730
John M Ruddy
42 Pantry Road, Sudbury, 01776
William M Brown
2 Baron Park Lane, Apt. 33, Burlington, 01803
Robert T Dunn
H04M 11/00
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