GB460698A - Improvements in and relating to trunk communication cable installations provided with amplifiers - Google Patents

Abstract

460,698. Multiplex systems. SIEMENS & HALSKE AKT.-GES. July 13, 1936, No. 19443. Convention date, July 20, 1935. [Class 40 (iv)] A multiplex carrier system comprises a number of stations connected by cables containing a few lines, e.g. four, capable of transmitting frequencies up to one or more megacycles, concentric conductors, stranded double or spiral quads being used. The traffic requirements between the various stations are different, the frequency range transmitted over an interstation section increasing with the number of channels to be provided, and owing to increase of attenuation with frequency the number of intermediate amplifiers in a section is determined by the number of channels required. Amplifiers are also provided at the stations. A separate cable containing one or more lines is preferably used for each direction, but if the. cross-talk damping between the lines of the two directions is large, a common cable may be used. The sections preferably have uniform electrical constants such as attenuation and characteristic impedance, but if a part of the network requires only a small number of channels, a different type of cable may be used. The various carrier frequencies are obtained by multiplication from a fundamental frequency supplied to all the stations over a separate line which may be inside the inner conductor of the concentric type of line, or the fundamental may be supplied over parallel connected wires of the twisted double or spiral quad. The lower frequency range is preferably used for long distance traffic, but it may be necessary to change the carrier frequency of any particular message from section to section. Operating potentials for the intermediate amplifiers are supplied from the stations over the transmission lines or separate lines. The system may be used for the transmission of telephony, telegraphy or television. In the example described with reference to Fig. 2, the stations A ... F being approximately 75 km. apart, a single line is used for each direction and the traffic between G and A, B, F requires 35 channels extending up to 200,000 #, no intermediate amplifiers being required. The traffic between C and B, G requires 120 channels extendingup to 800,000 # and one intermediate amplifier is provided in each section, whereas traffic between C, D, E, F requires 250 channels and two intermediate amplifiers are provided in each section. If traffic requirements over a section increase, additional amplifiers are provided. In the case of a section such as B, C, the existing amplifier may be replaced by two spaced amplifiers suitable for the extended frequency range or the existing amplifier may be byepassed for the additional higher frequency channels and two further amplifiers byepassed for the original band and dealing only with such channels are inserted in the section. Or the range of the existing amplifier may be extended and other amplifiers, either of the full range or for the higher frequencies only, are inserted.