Patent GB-341545-A (GB)
Title: Telephone transmission system employing repeaters
IPC: H04B3/20
Filed: 1929-10-19
Abstract: 341,545. Two - way repeaters. STANDARD TELEPHONES & CABLES, Ltd., SANDEMAN, E. K., THOMAS, P. R., and DUNHAM, C. R., Columbia House, Aldwych, London. Oct. 19, 1929, No. 31792. [Class 40 (iv).] The two paths over a two-way repeater are adapted to be connected directly to the two-wire lines by switches operated by incoming signals, each path being normally disconnected from one line. A common delay network may be provided for the two paths, the network being associated with the paths by hybrid coils or connected to the desired path by switches, and a common power amplifier may be connected up by switches, or a common network and power amplifier may be permanently connected in both paths. In the arrangement shown in Fig. 1, the path from W to E comprises amplifier 1 normally connected to W, hybrid coil 16, delay network 15, hybrid coil 17 and amplifier 2 normally disconnected from E. The path from E to W passes correspondingly over 3, 17, 15, 16, 4. The characteristic impedance of the network 15 is substantially a pure resistance, and balancing resistances 18, 19 are connected to the hybrid coils. Speech currents incoming over W and amplified at 1 are applied to the delay network 15 and to an amplifierrectifier 6 so that relay. 10 connects amplifier 2 to E before speech currents arrive over 15. For speech in the other direction, amplifier-rectifier 5 operates relay 7 to complete the path. The circuit is stable in the non-operative condition provided there is no capacity coupling between the two paths at contacts of relays 7, 10, and a construction of relay to obviate this coupling is described later. The hybrid coils may be replaced by relays (Fig. 2, not shown) the delay network 15 being normally connected over contacts of a relay at 16 to amplifier 1 and over a contact of a relay at 17 to amplifier 3, the relays at 16, 17 being respectively operated when relays 7, 10 are operated. In the modification shown in Fig. 4, a common second stage amplifier 30 is used for both paths, and the inputs of the amplifier-rectifiers 5, 6 are taken respectively from the penultimate valves of the first stage amplifiers 1, 2 so that rectifiers 5, 6 are not effective for currents incoming over E and W respectively. The delay network is inserted at 15. In a modification, Fig. 5, of the last described arrangement, the common second stage amplifier is disconnected from the outputs of the first stages 1, 2 at contacts of relays 8, 9. When speech currents arrive over W, relay 9 is operated simultaneously with relay 10 so that delay network 15 is connected between amplifiers 1, 3. In a modification of Fig. 5 (Fig. 6, not shown), the rectifiers 5 and 6 are fed from the outputs of amplifiers 1 and 2 but the network 15 is connected to the outputs of these amplifiers over back contacts of relays 8, 9 so that when speech currents arrive over W, rectifier 6 and amplifier 2 are disconnected from the network before currents proceeding over the network reach rectifier 6. This arrangement prevents amplifier noise from both amplifiers being applied simultaneously to the network, and the arrangements shown in Figs. 4 and 5 may be modified to obtain this advantage by the use of relays to short-circuit one or other of the amplifiers 1, 2. Electric contact-making relays. To prevent capacitative coupling between the circuits controlled by the relays, the springs 21 .. 24 are screened, contact between these springs and the armatureoperated springs 20, 25 being effected through holes in the screens.