Patent GB-439752-A (GB)
Title: Improvements in telephone repeaters
IPC: H04B3/20
Filed: 1934-08-17
Abstract: 439,752. Two-way transmission. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Western Electric Co., Inc. ; 195, Broadway, New York, U.S.A.) Aug. 17, 1934, No. 23794. [Class 40 (iv)] In two-way repeaters designed to prevent singing at all times whilst giving each party in a conversation complete freedom to interrupt the other, the voiceoperated control devices for the two directions are always at least partially operative and their output circuits act differentially on switching means such as a polarized relay or relays which redistribute the attenuation between the two repeater paths in accordance with the desired direction of transmission. In one arrangement, Fig. 2, networks H2, H<1>2, are normally connected in the two paths over back-contacts of relays G, G<1>, which are held in this position by biassing windings R, R<1>. When speech arrives from line A, say, the current in the output circuit of amplifier-detector E operates relay F over winding L but increases the bias against operation in winding M<1> of relay F<1>. Relay F connects up winding P of relay G and removes a short-circuit from winding Q so that relay G operates, removing network H2 from the transmitting branch and connecting resistance H<1>3 across resistances H<1>1, thus increasing the attenuation in the receiving branch and reducing the sensitiveness of amplifier-detector E<1>. Impedances S, T, U in the circuit of winding P are suitably chosen to provide any desired hang-over time in the release of relay G. In another arrangement, Fig. 3, in which the repeater remains fully operative in the direction in which it was last set by speech or noise of more than a predetermined intensity, complementary pairs of networks HI, H2 and H<1>1, H<1>2, are removed from the operative path and inserted in the return path by relays G, G<1>, controlled by a single polarized relay F differentially associated with the amplifier-detectors E, E<1>. Lamps Y, Y<1> serve as a visible check on the correct operation of relay F. Resistances X, X<1>, W, W<1>, permit the bias of the amplifierdetectors to be adjusted separately for high and low frequencies. The networks H<1>, &c. are designed to have a loss increasing with frequency and may incorporate the filter network of similar characteristics often included in the amplifier D as in Fig. 2. In a third arrangement, Fig. 4, (not shown), each attenuation network comprises series elements in one of the line conductors, the amplifierdetectors being connected up at intermediate points in the networks, and the armature of relay F, which has permanent-magnet biassing, being arranged to control direct short-circuits around the networks. Chattering of the contacts of relay F is reduced by connecting a pair of opposed rectifiers inductively across the rectifier circuit of E, Fig. 3. In a fourth arrangement, Fig. 5, connections of the amplifier-detectors at intermediate points of the networks H are effected by tapped connections to shunt impedances RC. The networks are designed to give greater loss at high and low frequencies than at intermediate frequencies, for use particularly with loaded cable circuits. The alternate biassing circuits of relay F are controlled by a second similar polarized relay AR. A slow-release relay L operated in series with F and AR reduces the sensitivity of these relays to prevent control by noise during pauses in speech. In a fifth arrangement Fig. 6, (not shown), each network is associated with the line-branch through a differentia transformer to the mid-point of which the input of the amplifier-detector is connected with a shunt resistance across one side to make the input and output impedances unequal. The circuits of the biassing winding: of relay F include the anode circuits of ther mionic valves, the grids of which are controlled in turn by the armature of F. A relay similar to L, Fig. 5, reduces the sensitivity of F by increasing the biassing current. In a sixth arrangement, Fig. 7, (not shown), the attenua tion networks contain rectifier elements anc have the property that the attenuation in creases with current-strength. In all arrange ments, the return branch may be completely blocked during conversation provided thai the blocking occurs at a point beyond the input to the amplifier-detector.