Patent GB-156065-A (GB)
Title: Improvements in telephone systems
IPC: H04M1/58
Filed: 1920-04-20
Abstract: 156,065. Western Electric Co., Ltd., (Assignees of Johnson, K. S.). Dec. 31, 1919, [Convention date]. Transformers.-An arrangement for preventing side-tone in telephone subscribers' or operators' circuits comprises a transformer with a threebranched core and with variously-arranged windings thereon connected to the receiver circuit, the transmitter circuit, the line, and a line-balancing impedance. This impedance may be omitted if the corresponding branch of the core is formed of different material or different cross-section from the rest. In the arrangement shown in Fig. 2, the central leg 12 of the transformer carries a winding 17 connected to the transmitter T. The side legs 13, 11 carry windings 19, 20 connected in series with the receiver R. The telephone line L and a linebalancing impedance N are connected respectively to windings 16, 18 on the legs 11, 13. For outgoing signals, variations in current in coil 17 produce opposite electromotive forces in coils 19, 20 and do not affect the receiver. For signals coming in on the line L, the receiver R is affected but not the balancing impedance N. The positions of the trarsmitter T and receiver R may be reversed. The coils 18, 19 may be combined in a single coil, as also may be the coils 16, 20. Fig. 6 shows such an arrangement, the receiver coils 19, 20 being combined with the coils 16<1>, 18<1>. In this modification, the balancing-impedance N is connected .n series with windings 18<1> and 17 and the line L in series with windings 161 and 17. The transmitter T is in the line circuit, permitting a central battery to be employed. Various transpositions of the receiver R, transmitter T, line L, and balancing-impedance N may be made, the coils 19, 20 always being connected in series with each other and with one of the above-mentioned elements. In an arrangement of operators circuits shown in Fig. 3, the receiver R and transmitter T receive direct current in series from the battery 21, the speech currents passing through condensers 23 to the respective transformer coils. An additional winding 24 is provided for supervising purposes. In a modification shown in Fig. 13, the balancing-impedance N is omitted, and the leg 13<1> of the transformer is made wholly or partly of a material having a lower permeability than the rest of the core. The sectional area of this leg may also be reduced. The Specification as open to inspection under Sect. 91 (3) (a) describes a two-way repeater, shown in Fig. 8 (Cancelled), comprising two transformers 26, 27 and two valves 29, 30. One line is connected to a coil 16 on the leg 11 of the transformer 26, a balancing-impedance N<1> is connected to the opposite coil 18, and the coil 17 on the centre leg is connected to the grid of the valve 29. The coils 19, 20 are in series in the output circuit of the other valve 30, being connected through a filter F2. The amplified currents passing through the coils 19, 20 do not affect the coil 17. In another arrangement only one valve and one transformer are used, the second line taking the place of the balancing-impedance N' and the coils 19, 20 being in the plate circuit of the singlevalve. This subject-matter does not appear in the Specification as accepted.