GB252752A - Improvements in duplex telegraphy - Google Patents

Abstract

252,752. Heurtley, E. S., and Muirhead & Co., Ltd. March 6, 1925. Duplex telegraphs; artificial lines.-In a duplex arrangement for a loaded cable A, A<1>, including an artificial line D, D<1> for balancing the cable, a long sea earth cable B, with inductance, resistance, and capacity characteristics similar to those of the corresponding length A of the main cable, is employed. The length of the cable B preferably exceeds 10 per cent of the length of the cable A, A<1>. The sea earth may be provided with a terminal impedance b<1>, as described in Specification 198,978. A network E, connected in series with the cable A, A<1>, as described in Specifications 193,957 and 198,978, may be provided to balance the sea earth as regards resistance and capacity. The artificial line mav comprise a home section D<1> balancing the portion A of the main cable as regards resistance and capacity, and a main section D balancing the remaining portion A<1> as regards inductance, resistance, and capacity. The inductance of the section D<1> may correspond to that of the network E. Combinations of resistance and capacity or inductance may be placed in one or both of the arms C, C<1> of the bridge to compensate for frequency variations as described in Specification 228,309. The arrangement enables the use of a transmission E.M.F. not exceeding 10 volts and of high amplification e.g. 50-fold at the receiver. The term " sea-earth " is intended to include a similar distantly-earthed conductor applied to land lines. Eliminating effects of disturbing currents.- Disturbing effects may be further reduced by the use of a balanced conductor forming with the cables A, B a multi-cored cable as described in Specification 20787/11.