GB750097A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

750,097. Unattended repeaters. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 27, 1954 [July 3, 1953], No. 18568/53. Class 40 (4). [Also in Group XXXVIII] In an electrical signalling system a number of stations employ a common tone frequency interrupted at different cadence frequencies for signalling over a common channel, the cadence being characteristic of the signalling station and serving to identify it at a remote point. The invention is applied in a carrier wave transmission system to the signalling of fault conditions at unattended repeater stations in to a control station. Several tone frequencies may be used if there are a large number of stations. The interruptions may be controlled by a galvanometer relay or by electronic means, and identification may be effected by a plurality of galvanometer relays mechanically tuned to different resonant frequencies, or by the integrating arrangement shown. Signals incoming at C pass through a filter F1 tuned to the tone frequency to a flip-flop circuit T which resets in a time less than the interval between pulses of the fastest cadence used. Thus pulses of uniform length are produced, the spacing of which is indicative of the calling station. These are applied to an integrating circuit comprising condenser C2 shunted by a resistance R in series with a milliammeter M which may be calibrated to indicate the station concerned.