GB631151A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

631,151. Automatic control systems for amplifiers. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and TERRONI, T. B. D. Oct. 29, 1947, No. 28817. [Class 38 (iv)] In an open-wire carrier telephone system, changes in the attenuation of the transmission circuit are counteracted so as to maintain the normal transmission level, by an amplifier, the gain of which is automatically adjusted in accordance with its output. As shown, Fig. 2, the incoming signal is applied to the primary of transformer TRA, of the level controlling amplifier LCA, the secondary of which energizes the potentiometer, comprising variable condensers C1, C2, which are mechanically coupled so that as one increases, the other decreases. The common point of Cl, C2 is connected to the grid of VA supplying the group amplifier GA, the output of which is applied to the pilot receiver PR, similar to that described in Specification 609,120, [Group XXXIX], and the pilot frequency is selected by filter PFF. The latter energizes the control equipment CE, in which the D.C. current is proportional to the level of the incoming signal. According as the line attenuation is ¢ a decibel above or below normal, so the contacts SL1 (H) or SL1 (L) are closed and the motor M, which positions C1, C2, is driven accordingly. A time delay is incorporated so that transient level changes do not effect the device. The change of gain of LCA, in decibels, is linear with respect to the angular movement of the motor M and a linearly-calibrated indicator may be mounted on the motor shaft.