Racal Acoustics Limited

Paul Q Barrett

Anthony G Gorman

Peter L Smith

A telephone communication method provides simultaneous duplex channels between respective pairs of stations over a single wire pair highway by frequency division multiplexing. Each duplex channel has a predetermined pair of carrier frequencies, but only carrier frequency pairs of channels in use for communication are present in the highway at any time. On initiating a call, a station seeks for a free channel and reserves it by generating the 'go' carrier of the free channel modulated with the call sign of the desired station, and also generating an alert signal. Quiescent stations respond to the alert by seeking a 'go' carrier with call sign data and, on identifying their own call sign, generating the corresponding return carrier to set up the channel.

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Hemel Hempstead, United Kingdom

Paul Q Barrett