Patent GB-728417-A (GB)
Title: Improvements in and relating to the supervision, distant control, or fault-location of transmission systems
IPC: H04J1/10
Filed: 1953-04-29
Abstract: 728,417. Two-way transmission. FELTEN & GUILLEAUME CARLSWERK AKT.-GES. April 29, 1953 [May 23, 1952; March 10, 1953], No. 11813/53. Class 40 (4). A signal which is periodically transmitted from one end of a twoway transmission system for controlling, supervising, or fault testing intermediate unattended amplifying stations is returned to the transmitting end by each intermediate station in turn, the forward progress of the signal from one station to the next being blocked and the return signal path completed only while a polarized relay responsive to the arrival of the signal frequency at the station is in its released position. This relay pulls up as soon as the signal frequency is received so that the return signal occurs only during its response time. If necessary, the return signal may be prolonged by initially transmitting a low-level signal and subsequently increasing the level sufficiently to pull up the relay. Alternatively, the signal may comprise two pulses, the first pulse being of insufficient duration to operate the relay which responds only to the second pulse. For identification purposes the length of the first pulse may be varied. In the embodiments described, different frequency bands 24-216 kc/s. and 264- 456 kc/s. are transmitted in the A-B and B-A directions respectively; and the condition of the system in each direction is constantly indicated by continuous pilot signals fp1 and fp2 of 220 kc/s. and 256 kc/s. Four-wire transmission, Fig. 1. Each intermediate station comprises amplifiers V1A, V1B for the A-B and B-A directions respectively. A 20 kc/s. controlling &c. signal fs1 is periodically transmitted in the A-B direction and at the first intermediate station is applied to a polarized relay PR over a relay contact pr1, band-pass filter BP20 and a rectifier GL1, the forward transmission path being blocked to the signal frequency by a band stop filter BSp20. Prior to the relay response, the 20 kc/s. signal is frequency doubled at VD and at modulator M1 is modulated by the 220 kc/s. pilot signal fp1 which is selected by a band-pass filter BP220. The side-band frequency 260 kc/s. of the modulated output is selected by a band-pass filter BP260 and constitutes the return signal. When relay PR operates, the return signal is terminated and BSp20 is shorted by contact pr1 so that the signal fs1 passes to the next station. When the signal reaches the end of the system, a signal fs2 of 480 kc/s. is sent in the opposite direction to restore relays PR and contacts pr1, pr2 to their original position. This signal passes from station to station in the same manner as fs1 and the combined pilot and signal frequencies fp2, fs2 produce a 224 kc/s. return signal. Apart from the omission of frequency doublers and the different contact positions, the circuit arrangements in the two directions are identical. Two-wire transmission, Fig. 2. The A-B and B-A frequency bands are directed through a common amplifier V by low-pass and high-pass filters TP1, TP2 and HP1, HP2 respectively. The two signal frequencies fs1, fs2 are blocked by series-connected band-pass filters BSp20 and BSp480, only the latter filter being initially short-circuited. The circuit arrangement is otherwise similar to the arrangement used for four-wire transmission.