Application of voice-frequency signalling to C.L.R. service in Belgium
14 October 1935
The paper describes the replacement of the 50-cycle signalling system by a 2-frequency voice-signalling system using alternating currents of two frequencies within the speech range, viz., 600 and 750 ~. Ordinary telephone relays in combination with valves and a system of filters are used instead of voice-frequency relays. The extremities of the telephone circuits are connected to signalling panels which receive, amplify and rectify the voice-frequency currents and pass them on to the automatic equipment as regular d.c. signals. An explanatory diagram of the signalling panel accompanies the paper. Two-frequency signalling has been installed between Antwerp and Verviers with a repeater at Brussels and between Brussels and Verviers.