GB465464A - Improvements in or relating to the control of variable attenuation of networks for alternating signalling or like systems - Google Patents

Abstract

465,464. Two - - way transmission. TELEPHONE MANUFACTURING CO., Ltd., BURRIDGE, B. J., and PADDLE, L. H. Nov. 1, 1935, No. 30253. Addition to 442,947. [Class 40 (iv)] [Also in Group XL] The system described in the parent Specification which involves the application of control voltages derived by rectifying A.C. signals from two sources to different points of a multi-branch circuit for the control of attenuation networks deriving their normal bias voltages from such circuit is modified by amplifying the signals before rectifying and applying the control voltages in direct opposition to each other and simplifying or omitting the multi-branch circuit. As shown in Fig. 1 control signals on circuits S1, S2 are amplified and rectified and produce voltages across resistances R3, R4 acting in opposition on the networks N1, N2. Signals from S2 also operate a relay X which short-circuits itself. Normal bias for the rectifiers is supplied by battery BT. In one modification only one, and in another neither of the networks has an initial bias. In another arrangement, Fig. 4, the control signals act on four networks N1 .. N4 which may have different initial bias so that they change their state in a predetermined order. A further arrangement, Fig. 5 (not shown), resembles that shown in Fig. 4 but the transformers T3, T4 have separate secondaries for N1, N2 and N3, N4. In a further modification, Fig. 6, adapted for very weak signals, the valves V<1>, V<2> amplify alternating current from a local source such as AC1 and the incoming signals either block or unblock these valves, the output from which is rectified and controls the networks as in the other systems. The circuit VC automatically limits the value of the resulting currents.