GB408264A - Improvements in telephone systems - Google Patents

Abstract

408,264. Anti - - side tone circuits. LOWE, J. P., 7, Montpelier, Edinburgh. Sept. 30, 1932, No. 27171. [Class 40 (iv).] An anti-side-tone circuit comprises a group of pairs of windings A associated with the line and a second group D associated with the receiver R. The secondaries of one group are connected to the primaries of the other to form a closed circuit with which the transmitter T is associated by means of a transformer C, the secondary of which is connected between intermediate points of the combined line secondary and the combined receiver primary. Two adjacent line primary windings or, as shown, secondary windings, are wound in opposition so that when current is received from the line an E.M.F. is induced across only one half of the combined line secondary and a resultant current flows in the receiver. When the transmitter is energized no resultant current flows in the receiver circuit, but the current in one half of the combined line secondary induces currents in the line. Each primary and secondary pair may be a separate transformer. The degree of reduction of side-tone may be made adjustable by the provision of tappings on the transformer D for connection of the secondary of transformer C or of variable resistances or inductances. In a modification, the invention is applied to an operator's set. The transformers C, D may be transposed.