| 摘要 |
669,334. Telephone &c. transmission systems. LIGNES TELEGRAPHIQUES ET TELEPHONIQUES. Feb. 3, 1949 [Feb. 25, 1948; June 14, 1948], Nos. 3059/49 and 3060/49. Class 40 (iv). In a coaxial line telecommunication system wherein power is supplied to unattended repeater stations over the transmission line, at least two coaxial lines are used, one for each direction of transmission, and a dual amplifier is provided at each station for each direction of transmission, each half of each dual amplifier being fed from a separate power source to enhance operational reliability. The power supply system is normally balanced so that only a very small resultant current flows in the outer line conductors and in the event of a fault the increased supply current flow is utilized to signal the fault. As shown, Fig. 1, signal transmission is effected from a main station 1 over a high-pass filter 7 and coaxial transmission line 3 to a repeater station 2 where the signal is passed by a high-pass filter 10 to a dual amplifier comprising two portions 11, 12 in parallel and then through a further high-pass filter 15 to the transmission line 16 leading to the next station. Transmission in the opposite direction is from line 17 by way of high-pass filter 18, dual amplifier 19, 20, filter 23 to line 4. Independent power sources S, S<SP>1</SP>, at the main station 1 feed the repeater station 2 over low-pass filters 5, 6 and the respective transmission lines 3, 4 where the respective power supplies are fed over low-pass filters 24, 28 to power supply devices 25, 29 and, if necessary, over lines 26, 30, low-pass filters 27, 31 and the lines 16, 17 to the next repeater station. The power supply device 25 feeds the amplifier portions 12, 20 and the device 29 feeds the amplifier portions 11, 19 so that each half of each amplifier is fed from a separate power device and should one power supply fail the transmission system will still function. A constant current type of power supply system may be used in lieu of the constant voltage system shown. In cases where an emergency power source is switched in manually or automatically upon occurrence of fault in the normal supply, the two sources according to the invention may be derived from a single source, Figs. 3, 4 (not shown). Fig. 5 shows such a single power source S at the main station 1 which develops the two supplies through transformer 36 having a centre-tapped secondary. At the repeater station 2, each power supply after separation by its respective low-pass filter 24, 28 is applied through a transformer 37, 38 to its associated power supply device 25, 29. The outer conductors of the lines 3, 4 which form the common return for the two power supplies are connected together at the ends of each section so that the resultant power supply current therein is very small. Any increase therein caused, e.g. by a fault in one of the power supply devices such as 25, 29, will be indicated on an ammeter A in the common return and may actuate an alarm. The transformer 36 may be replaced by two separate transformers, Fig. 6 (not shown), and a resistor or impedance network, Figs. 7, 8 (not shown), may be series connected in the circuit feeding the power supply transformer so that when a fault occurs on one of the power supply lines its effect is counteracted in the other supply circuit by the decrease in the potential drop across the impedance. |
