GB442947A - Improvements in or relating to the control of variable attenuation networks for alternating current signalling or like systems - Google Patents

Abstract

442,947. Transmission systems. TELEPHONE MANUFACTURING CO., Ltd., Martell Road, West Dulwich, London, and BURRIDGE, B. J., 1, Highview Avenue, Wallington, Surrey. Aug. 18, 1934, No. 23889. [Class 40 (iv)] Variable attenuation networks controlled by varying the direct current flowing therethrough are conductively connected in a multi-branch or bridge circuit to which a source of D.C. is applied for determining the normal condition of the network and the branches of which comprise resistances or two-terminal (diode or metal) rectifiers, the variation in D.C. for control purposes being obtained over conductive connections to one or more of the branches. The control may be manual or by rectified alternating signal current from one or more channels. Fig 4 shows an arrangement for controlling four networks by the application of a control voltage to one of the arms of a multibranch circuit R1 ... R7 the terminals of which are suitably connected to a D.C. source to determine the initial biassing currents. In another arrangement, Fig. 6, using a simple bridge circuit each of one pair of bridge arms consists of a pair of rectifiers and these, in the case of one arm, take part in a voltage doubler rectifying circuit to which an alternating control current is applied. The invention is shown in its application to an echo suppressing arrangement in a repeater, Fig. 7 (not shown). In a further application, Fig. 8, to the control of two loud-speaker circuits, four networks MS1, C1, MS2, C2, connected in series are controlled by a bridge circuit the junction points of the networks being connected to a D.C. source and ground to provide normal biassing currents. The networks MS1, MS2 control the transmission paths whereas C1, C2 control the control paths. In Fig. 1 two output circuits of a triode are made effective one at a time by manual control at SW of one of the arms of the bridge. Fig. 2 shows the application of the invention to a system in which the substations of a telephone system can be effectively connected at the will of an important official to a common circuit L to which the official is connected. This system forms the subject-matter of Specification 443,011. Normally, the connections between the substations and the common line are blocked at the networks CN1-CN3, the normal telephone channels IN1-IN3 to the substations being effective over networks N1-N3. By means of key SW3 or selector SW4 respectively all or any of the networks CN1-CN3 may be conditioned for speech between the substations and the common line, the corresponding networks N1-N3 being simultaneously blocked. In the further arrangement shown in Fig. 3 a network N1 in the output circuit of a diode-triode is controlled by application to bridge arm R3 of control voltage derived from the diode portion of the valve.