Patent GB-416865-A (GB)
Title: Improvements in or relating to carrier current signalling systems
IPC: H01B11/20
Filed: 1933-03-23
Abstract: 416,865. Wired wireless signalling. STANDARD TELEPHONES & CABLES, Ltd., Connaught House, Aldwych, London.-(Western Electric Co., Inc. ; 195, Broadway, New York, U.S.A.) March 23, 1933, No. 8777. [Class 40 (v).] A carrier signalling system comprises a cable made up of a plurality of pairs of coaxial conductors and means for transmitting signals in the same frequency range in opposite directions over said conductors. In one such cable, the central layer comprises four coaxial pairs 10, Figs. 4A, 4B, and a second layer comprising ten pairs 11 bound with tape 8 and enclosed in a lead sheath 9, over which may be placed a bedding of jute and armouring material. In another example the central portion only of the space within the sheath is occupied by coaxial conductor pairs 13, Fig. 5, the remainder being filled with twisted pair circuits 12, while in a further example (Fig. 6, not shown) the central region is filled with twisted pairs surrounded by coaxial conductor pairs. The central conductor of each coaxial pair may comprise a number of strands of fine insulated copper wire braided or twisted together, preferably, by twisting three strands together to form a group, then twisting three groups together to form other groups and then three of the latter to form " ropes " and so on, six stranding operations resulting in a cable of 729 strands. A construction may be adopted such that the current density decreases as the centre of the conductor is approached, for example by weaving the strands so that the distance between them increases toward the centre of the conductor or by arranging the strands so that they travel more nearly longitudinally at the outside of the conductor and more nearly circumferentially or radially toward the centre. Alternatively the interior may be hollow or comprise a core of string &c., or the insulation of the strands may be poor, or leakage may be induced by using very long stranding pitches so that a strand is near the centre of the conductor for a considerable distance. The outer conductor may also be braided and both may consist of ribbon wound into a tubular formation. The conductors are spaced apart by spiders, beads, a helically wound ribbon, or threads braided into the conductors. Conductors may be branched off the main cable where required and a system using such a cable is shown in Fig. 8, and comprises circuits for a city A terminating an extensive communication system, suburban points B, a nearby city D and distant cities E. At the terminal A are located several exchanges S1, S2, S3 each comprising outgoing low frequency circuits 21, modulators 23, and bandpass filters 25 and also incoming band-pass filters 26, demodulators 24, and low frequency circuits 22, the stations being connected to the main high frequency cable 36 through subsidiary cables 29, 30, 31 feeding a cable 35, the number of conductor pairs in each cable depending on the number of low frequency channels it is desired to accommodate. Another cable 37 from various suburban points joins cable 36 to form cable 38 leading to the city D. Some of the conductors of cable 37 may branch into cable 36 and make a T-connection with through circuits between points A and D. At D, cables 40, 41 carrying signals in opposite directions are branched off through repeaters 42, 43 to a cable 45 leading to the distant city E, while the remainder of the conductors, in cable 39, are connected through circuits 49, 50 to outgoing and incoming single pairs of coaxial conductors 51, 52 of large diameter and carrying a very wide band of frequencies. The minimizing of cross talk by insulating and specially arranging the individual conductor pairs is discussed.