GB395035A - Improvements in or relating to telephone or like signalling systems - Google Patents

Abstract

395,035. Echo-suppressors and like control circuits. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Dudley, H. W. ; 123, South Oraton Parkway, East Orange, New Jersey, U.S.A.) Jan. 13, 1932, No. 1063. Convention date, Jan. 30, 1931. [Class 40 (iv).] A control circuit, e.g. an echo-suppressor, which discriminates between speech or signal currents and noise currents comprises an element adapted to operate only in response to an unequal distribution of energy over a certain frequency range. As shown in the Figure, the windings of the differential relay 4 are connected to parallel circuits including amplifier-rectifiers 7, 10 and selective circuits 8, 11 (tuned circuits or bandpass filters) which transmit adjacent sub-bands of small width, so that noise currents produce no effect since the energy in the sub-bands is substantially the same. In an extension of this arrangement, three parallel circuits transmitting adjacent sub-bands are connected in pairs to three differential relays having their contacts arranged in parallel. The Specification describes the application of the control circuit in the terminal station of a four-wire system with radio links employing control currents of frequencies outside the speech band which flow concurrently with the speech currents, filters being provided to confine the speech and control currents to their proper channels. Specifications 142,115 and 206,715, [both in Class 40 (iv), Telephones &c.], are referred to.