GB374528A - Coupling a two-way path to two one-way paths in electric signalling systems and devices therefor - Google Patents

Abstract

374,528. Two-way transmission. STANDARD TELEPHONES & CABLES, Ltd., LATIMER, K. E., and RENDALL, A. R. A., Connaught House, Aldwych, London. March 16, 1931, No. 8036. [Class 40 (iv).] A hybrid coil for connection to a two-way line without the interposition of repeating coils, and having the windings of the twoway line, two one-way lines and balancing network insulated from each other, is so arranged that currents flowing through the conductors of the two-way line in parallel (phantom circuit, simplex telegraph or interference currents) and passing through the phantom tap to other circuits or through the self capacity of the windings to earth, do not give rise to currents in the one-way paths. The output and input windings in the one-way paths may be connected directly in the grid or anode circuits of the amplifying valves. Arrangements are also described for varying the ratio of the windings and for using the same coil on lines of different impedances, and for connecting the coil to the one-way paths over a second hybrid coil. In the arrangement shown in Fig. 2, the line windings are subdivided and cross-connected to obtain the desired result. To provide against interference only, the capacity to earth or other point of the line windings is concentrated at the points of connection of the windings to the two-way line. This may be done, as shown in Fig. 6, by enclosing the line windings in a live shield and interposing shields, preferably earthed, between the live shields and the one-way windings ; or a one-way path winding and the corresponding network winding are wound first on a spool followed by an earthed screen and then the corresponding line winding the inner end of which is connected to line, the other windings being similarly arranged on a second spool. In the modification shown in Fig. 4, a coil H with cross-connected windings as in Fig. 2 is provided with modified input and output windings connected to the one-way paths R1, R2 by a second hybrid coil W4, W5, W6. The impedance of the lines may be equalized over jacks J used also for measuring. The arrangement shown in Fig. 5 using a coil in which the line to network ratio is not unity may be applied to the arrangements previously described. This arrangement may be used to work on lines of two different suitable impedances by interchanging the line and network connections, and the gain may be measured by an instrument having only one of these impedances. Tappings may be used to connect to lines of other impedances and to obtain gain measurements. As shown, the hybrid coil may be arranged to work with line of impedance 2R, R, or ¢R (tapping) but when the cross-connection method, Fig. 2, is used, an additional winding is preferable to the tap.