GB510830A - Cross talk reduction - Google Patents

Abstract

510,830. Preventing inductive disturbance. STANDARD TELEPHONES & CABLES, Ltd. Sept. 2, 1938, No. 25741. Convention date, Sept. 22, 1937. [Class 40 (iv)] [Also in Croup XXXVI] In order to reduce cross-talk in a highfrequency cable comprising a number of pairs or two-pair quads, each repeater section is divided into two halves and the far-end crosstalk is measured in magnitude and phase at a selected frequency between the various pairs in both half-sections, after which the pairs are spliced together so that the unbalances in one half-section compensate as far as possible those in the other half-section. In the case of quads, the quads may be split, that is, the pairs of a quad in one half-section may be connected to .pairs in different quads in the other halfsection, but preferably the quads are spliced together without splitting in accordance with the within-quad cross-talk values in the halfsections. As shown, the cross-talk between two pairs 1, 2 is measured by means of a capacity bridge 3 and a resistance bridge 4 with corresponding arms in shunt. The test frequency is applied at one end of pair 1, and the far end of pair 2 is connected to the bridges 3, 4, the output of which feeds a telephone receiver 7 through an amplifier 5 and filter 6, and the bridges are adjusted to give zero output. The resistance bridge measures the inductance unbalance component which is at right angles to the capacity unbalance and usually predominates. An inductance bridge may be used instead of the resistance bridge. Although the cable is used for high frequencies, it is found that a test frequency of 1000 cycles gives satisfactory results. Any residual cross-talk may be reduced by the use of balancing units of the kind described in Specification 468,735. According to the Specification as open to inspection under Sect. 91, the splicings may be made in accordance with the inductance unbalance values only. This subject-matter does not appear in the Specification as accepted.