Improvements relating to the reduction of the far-end crosstalk in trunk communication cables

摘要

427,365. Preventing inductive disturbances. SIEMENS & HALSKE AKT.- GES., Siemensstadt, Berlin. April 10, 1934, No. 10803. Convention date, April 10, 1933. [Class 40 (iv)] [See also Group XXXVI] Far-end cross-talk is reduced by making the ratio of the capacitative to the magnetic couplings equal or substantially equal to the ratio of capacity to inductance of the pairs or quads. Either of the quantities in question may be adjusted to bring about desired equality of ratio. The couplings may be varied by additional condensers or magnetic coupling elements as described in Specifications 147,013 and 304,229, [both in Class 40 (iv)], respectively. The actual capacity or inductance of the lines may be adjusted or varied in the construction of the cable or by choice of circuits in the cable. If the distance between a line and a surrounding conductive screen or surrounding lines is made sufficiently large relatively to the distance between the cores of a line, the line capacity is independent of the presence of the screen, and the ratio of capacity to inductance can be given a desired value by varying the distance between the cores. Another method consists in enclosing each core in a closed or meshed screen so that the inductance can be varied independently of the capacity by varying the distance between the cores, the capacity being determined by the thickness of the insulation between a core and its screen. Crossing between cores may also be utilized for this purpose and also to reduce near-end cross-talk. In the cable shown, eight cores individually screened are stranded around a central portion 10 of insulation containing air spaces or comprising a bundle of cores. The eight cores are surrounded by further insulation 12 or a layer of cores, and an outside sheath 13. Different inductance values can be obtained, e.g. by selecting cores 1 and 2 or 1 and 5 for a pair. When diametrically opposite cores are all used as pairs, couplings may be varied by crossings according to a definite plan, and when cores 1, 5, 3, 7 and 2, 6, 4, 8 are used as quads, the two quads as a whole may be crossed at definite intervals or other interchanges in the relative position of the cores may be effected. A number of groups as shown may be stranded together to form a larger cable. The couplings may also be varied by introducing short lengths of magnetic or non-magnetic screens of different thicknesses or materials or by using different kinds of cable, e.g. continuously or lump loaded.