GB985968A - Improvements in or relating to telecommunication systems - Google Patents

Abstract

985,968. Preventing inductive disturbance. POSTMASTER-GENERAL. May 5, 1961 [May 10, 1960], No. 16525/60. Heading H4R. A telecommunication system having at least two wires exposed to an interfering field includes an amplifier whose output voltage is applied to the wires so as to oppose the induced interfering voltage and whose input voltage is derived from one of the wires, this input voltage being the difference between the said induced and the said output voltages. A voltage E is induced in the line wires 2-4 and test wire 1 by an interfering field in the region 6. The test wire is connected to the input 13 of an amplifier 14 whose output is connected to the primary winding of a transformer 8. A number of secondary windings 9-12 are connected in series with the respective wires 1-4 and they may be effected by simply wrapping the cable (carrying wires 1-4) around the core of the transformer a number of times or by passing the cable through the core. It is shown mathematically that by making the gain of the amplifier sufficiently high consistent with stability the opposing voltage e induced in the wires is equal (or nearly equal) to the interfering voltage E and consequently the interfering voltage is virtually cancelled. This is achieved without any need for precise adjustment of the components and is not subject to a decrease of neutralization with time.