Patent GB-492382-A (GB)
Title: Improvements in electric communication cables
IPC: H01B13/02
Filed: 1937-03-20
Abstract: 492,382. Cables. SOUTHERN UNITED TELEPHONE CABLES, Ltd., and JACKSON, C. G. March 20, 1937, No. 8276. [Class 36] [Also in Group XXV] To reduce crosstalk in a highfrequency communication cable comprising a plurality of circuits in the form of twisted pairs or quads, the conductors of each circuit are stranded with a lay which is continuously and repeatedly varied in the length of the cable, the variation being such that when the circuits are combined to form the cable the periods of variation (measured along the circuit) of any two circuits are either unequal at all points along the cable or are only equal at isolated points, the stranding being such that all the circuits have the same mean length of lay. The period of repetition of the cycle of variation may be constant for each circuit but different for the different circuits. Alternatively the period of repetition of the cycle may vary continuously. Fig. 2 shows a machine for stranding the circuits, the conductors being drawn from a bobbin carriage 1, which is rotated by a motor 5, by a capstan 19 which is also rotated by the motor 5 through a variable speed drive. The latter comprises a differential gear 10, 11, 14, 15, the cage-wheel 10 of which is driven through gearing 7, 8, 12, 13. The gear wheel 14 drives a shaft 9 geared to the capstan shaft. The ratio of the differential drive is continuously and repeatedly varied by a donkey crank mechanism 26, 28, 29, the crank disc 26 of which is driven through gearing 21-24 by the capstan shaft. The reciprocating rod 29 of the donkey crank carries a rack 32 which operates the control shaft 16 of the differential drive through a pinion 33 and gearing 30, 31. Reciprocation of the rod 29 varies continuously and repeatedly the speed and direction of rotation of the control shaft 16 thereby varying continuously and repeatedly the speed of rotation of the driving shaft 9 of the capstan. The mean length of lay of stranding may be changed by changing the ratio of the gears 7, 8, whilst the period of variation of the lay may be changed by a change of ratio in the gearing 21, 22. The amplitude of the variation of lay depends on the product of the ratios of the gears 21, 22 and 30, 31. Instead of the crank-disc of the donkey crank being driven by the capstan, it may be driven by the cage-wheel 10 of the differential gear. In a modified form of the machine, Fig. 5, the variable speed drive comprises an expanding pulley 36 driven by the shaft 6, the expanding pulley driving a capstandriving pulley 39 by a flexible band 40. The expansion of the pulley 36 is controlled by levers 41 which are operated by a screwed. shaft 42 driven by the donkey crank mecha,- nism. In the arrangement shown in Fig. 6 a continuous and repeated variation in the period of variation of lay is effected by employing a separate motor 48 to control the ratio of the variable speed drive 46, the motor being fitted with an automatic reversing switch 53 and the motor speed being made to fluctuate between definite limits by variation of a resistance in the field circuit of the motor, such as the resistance 58 which is varied by rotation of the capstan. In a modified form of the apparatus shown in Fig. 2, the donkey crank mechanism is replaced by means for applying a variable braking load to the control shaft of the differential gear. The load may comprise a oil pump delivering oil through a closed circuit containing a valve having a variable orifice, the area of the orifice being periodically altered between fixed limits by a reciprocating device driven by the capstan or the cage-wheel of the differential gear.