Patent GB-356209-A (GB)
Title: Electric telephone and like transmission systems
IPC: H04B3/20
Filed: 1930-06-04
Abstract: 356,209. Two-way repeaters. STANDARD TELEPHONES & CABLES, Ltd. and GROVE, S. H., Columbia House, Aldwych, London. June 4, 1930, No. 17224. [Class 40 (iv).] Two-way repeaters associated with a single circuit such as a submarine cable have their transmitting and receiving branches conditioned in accordance with the direction of speech by means of an auxiliary tone current or currents applied continuously to the line when not in use and withdrawn as soon as speech commences, and means are provided to prevent lock-up when speech commences in both directions substantially simultaneously. The system may comprise one or more intermediate stations. In one arrangement, Fig. 1, different tone frequencies T1, T2 are transmitted over the cable from A to B and from B to A respectively. Fig. 2 shows an intermediate station adapted to pass the tone signals straight through. Alternatively, the tone signals may be relayed by means of additional sources at the intermediate stations. In another arrangement, Fig. 4, the tone sources are provided at the intermediate station only. First arrangement, Fig. 1. Speech from line L1 passing to branch TB at station A operates relay S3 which by removing a short-circuit energizes relays S5 which switches off normally-applied tone T1 from the cable C, S6 which switches branch TB through, and S7 and S8 which are slow to operate the former having a period equal to twice the time of transmission of speech over the cable, and the latter slightly longer. At the end of this period, S7 puts an additional short-circuit on relays S9 and S10 to prevent their operation and S8 opens path TR. At station B cessation of tone T1 operates a polarized relay PR2 thereby removing a short-circuit from relays S12 which switches branch TR1 through, S13 which disables path TB1, and S14 which through relay S15 removes tone T2 from the cable. For speech in the other direction from B to A relay S18 causes the operation of relays S15 which removes tone T2, S16 which disables path TR1, and S20 which switches-through branch TB1. At station A cessation of tone T2 operates relay PR1 removing short-circuits from relays S1 which disables branch TB, S9 which switches-through branch TR, S10 which disables relays S6, .. S8, and S22 which through relay S5 cuts off tone T1. If speech in both directions, occurs substantially simultaneously so that tone T2 is cut off at B during the period of operation of relay S7, the operation of PR1 by the operation of S10 gives preference to the speech from station B. In order to prevent the operation of relay PR1 by the frequency T2 occurring in speech and passing from branch TB over coil H2 to branch TR, this frequency is initially removed from the speech currents by a filter F1 which is subsequently cut out by slow-acting relays S2, S21. Intermediate station, Fig. 2. The auxiliary-tone currents normally pass straight through via tuned amplifiers TA, TA1. When tone T1 is cut off, relay S23 releases causing the operation of relays S24 which switches-through the upper path, and S25 and S26 which act to block the lower path after a time interval in a similar manner to relays S7, S8, Fig. 1. For speech in the other direction, the release of relay S27 operates relays S28, S29 which act in a similar manner to relays S9, S10, Fig. 1. In an alternative arrangement, relays S23, S27 on release also disconnect additional tone sources which are normally applied at the intermediate station to the cable sections CW, CE, respectively. Modified arrangement in which auxiliary tone currents are only applied at an intermediate station, Fig. 4. Path TB at station A is normally connected up so that speech from line L1, passes over this branch and cable C to operate relay S23 at the intermediate station. Relay S39 causes relay S32 to remove tone T1 from cable CW, relay S24 switches the upper branch through, relay S26 disables the lower path, relay S38 withdraws tone T2 from cable C, and relay S35 disables corresponding relays for calls in the opposite direction. Relays S35, S36 are so inter-related that in the case of simultaneous speech preference is given to speech from the distant end to A.