Patent GB-446225-A (GB)
Title: Improvements in signal transmission systems involving unattended repeater stations
IPC: H04B17/40
Filed: 1935-05-24
Abstract: 446,225. Repeating systems. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Western Electric Co., Inc. ; 195, Broadway, New York, U.S.A.) May 24, 1935, No. 15212. [A Specification was laid open to inspection under Sect. 91 of the Acts, Dec. 10, 1935.] [Class 40 (iv)] In a system having several unattended repeater stations between attended stations, means are operated over a circuit common to several stations (e.g. the main transmission circuit), for giving an alarm if a fault occurs at any of the unattended stations and for enabling the faulty station to be identified. In one arrangement, Fig. 1, each station comprises a relay Re, Re1, &c. which is normally energized by the signal currents or by a special pilot current. If a repeater fails, the relay at that station and at all subsequent stations in the direction of transmission fall back. The relay Rey at the attended station Y gives an alarm Sy and those at the unattended stations put short circuits on a separate circuit L1 and so cause the operation of a further alarm S<1>x at station X. The attendant at station X identifies the faulty repeater by measuring the resistance of circuit L1. If the operation of S<1>x had been caused by a fault in the auxiliary arrangements, alarm Sy would not have been operated. In a modification, Fig. 2 (not shown), in which power for the repeaters is supplied in the form of alternating current over the transmission path, this path also provides the direct current alarm controlling and identifying path, each repeater being by-passed by a circuit which passes direct but not alternating current and the short-circuit controlled by the alarm-controlling relay being in the middle of this by-path. In further systems, Figs. 3, 4 (not shown), the auxiliary channel is fed at one end either permanently or when a fault alarm has been given with A.C. of several frequencies, one for each unattended station, and a repeater on failing shunts the auxiliary circuit with a series resonant circuit tuned to its individual frequency so that an indication is given at the other end of the channel of the repeater that has failed. The auxiliary channel may be a separate circuit or the main transmission circuit with by-paths round the repeaters for the identifying currents. In a further arrangement, Fig. 5, the failure of a repeater U1 causes a spare repeater U<1>1 to be connected up. Identifying frequencies, one for each repeater are constantly passed over the transmission circuit, two being by-passed round each repeater while the remaining one, which acts to maintain relay R at the station concerned normally operated, passes through it but not through the auxiliary repeater. Consequently when one repeater fails the frequency that normally passes through it fails to arrive at the other end of the circuit and an individual alarm is actuated. It may be arranged that a single spare repeater is provided at each unattended station common to both directions of transmission. Fig. 6 shows an identifying arrangement in which currents of frequencies individual to the unattended repeaters are connected to the transmission circuit in succession. Each station is arranged to select and rectify one particular frequency, the rectified current produced affecting an instrument LPx. When a repeater fails, this rectified current is not produced and the faulty repeater can thus be identified. In a further arrangement, Fig. 7, in which the indicators R are provided at the station at which the identifying currents are applied, the identifying frequency f1 passes from the W-E to the E-W path at the first repeater and so back to the testing station. Similarly, frequency f2 passes across at the second unattended station and so on. The filters between the two paths are very sharply selective and may employ crystal elements and preferably introduce a loss equal to that introduced by a line section. The indicators R merely identify the faulty station, not the actual repeater, but the latter can be deduced from the condition of indicators WSx, ESy. In a modification, Fig. 8, of the last described system, only two frequencies are employed, there being no frequency corresponding to, and no path between the oppositely directed transmission circuits at the middle one of three unattended repeaters. The two frequencies employed are sent from opposite ends. Each end also comprises a pair of indicators and a faulty repeater can be identified by comparing the readings of these indicators. In a further system, Fig. 9 (not shown), which is otherwise identical with that shown in Fig. 7, only two primary frequencies are employed, additional frequencies being derived from these in the paths between the signal transmission paths at the unattended station by modulation and filtering. Specification 416,867, [Group XL], is referred to.