GB853884A - Improvements in or relating to telecommunication systems - Google Patents

Abstract

853,884. Unattended repeaters. GENERAL ELECTRIC CO. Ltd., and INGRAM, D. G. W. Feb. 6, 1959 [Feb. 18, 1958], No. 5204/58. Class 40 (4). The gain of a negative feed-back amplifier at a repeater station is monitored at a terminal station by having a signal characteristic of the repeater and injecting it into the amplifier in such a way that the transmitted amplitude of the characteristic signal increases as the gain of the amplifier falls and increases more rapidly than the gain falls. The invention may be applied to a frequency or time-division multiplex system using radio or cable links. A repeater may have an amplifier, as shown in Fig. 1, comprising three stages of grounded emitter transistors the multiplex path being over the terminals 30, 31 to 32, 33 and a local oscillator (not shown), producing a characteristic frequency of a given amplitude which when connected across terminals 50, 52 in the output circuit produces an output across the terminals 32, 33 of an amplitude comparable with that of the multiplex signals. The frequencies of the characteristic signals are chosen to lie below or above those used for the multiplex transmission. Reduction of gain produced by deterioration of components causes the amplitude of the characteristic frequency appearing at terminals 32, 33 to increase by virtue of the feed-back path which includes resistor 45 and capacitor 48. Separate amplifiers may be used in the go and return paths in which case the same characteristic frequency may be injected into both amplifiers at each repeater station and each terminal station receives gain monitoring signals relating to the incoming path only. If a common amplifier is used for both directions of transmission only one terminal station receives the signals. All characteristic signal frequencies may be filtered out of the transmission path at a terminal station and by mixing with the output of a variable oscillator each frequency in turn may be changed to a fixed frequency which is filtered, rectified, and used to indicate the gain of its amplifier.