GB517167A - Improvements in and relating to methods of regulating the amplitude of electric waves - Google Patents

Abstract

517,167. Automatic volume control. STANDARD TELEPHONES & CABLES, Ltd., and TERRY, V. J. May 21, 1938, No. 15179. [Class 40 (iv)] [Also in Group XL] A circuit for responding to impulses, e.g. successive half-cycles of alternating current, in telegraphy, rejects impulses of an amplitude below a certain value, this value being variable with the rate at which impulse energy is being received and being equal to half the peak value of the incoming signals, and limits the amplitude of the accepted impulses to a value which is the same for positive and negative half-cycles. As shown the first function is performed by a bridge rectifier 3 ...6 having its input terminals in series in the transmission circuit and its output terminals bridged by a circuit comprising a condenser 15 and leak 14. In a modification, Fig. 2 (not shown), a similar rectifier has its input bridged across the transmission circuit and its output connected to a circuit comprising an inductance and resistance in series. The impedance of the bridge and consequently the level below which signals are rejected depends on the charge on condenser 15 (or the current in the inductance). The second function is performed by a full-wave current limiter comprising a battery 18 and a rectifier 12 for one direction. The other direction is looked after by the battery 19 and either the valve 10 which passes the signals on or another rectifier 11. Since the batteries 18, 19 are equal the output is free from even harmonics when the input is sinusoidal and since the level below which signals are rejected is made equal to half the peak value of the alternating input impulses the output is, for large values of signal, free from third harmonic also.