GB541438A - Carrier lead-in cable loading systems - Google Patents

Abstract

541,438. Telephone &c. transmission. STANDARD TELEPHONES & CABLES, Ltd. Aug. 23, 1940, No. 13397. Convention date, Dec. 13, 1939. [Class 40 (iv)] [Also in Group XL] A section E for matching the impedance of an open-wire line OL which may have various characteristic impedances to a lead-in cable LC which may have various lengths is applied between the end of the cable LC and the filter 6 and includes an adjustable series inductance L and adjustable condensers CA, CB. In the case of longer cables, a fixed impedance matching section G is added between a cable and the open-wire line. The system is particularly applicable to disc-insulated lead-in cables, which have a relatively high inductance and low capacity, and to a broad-band carrier system in which twelve carrier channels lying between 36 and 142 kc/sec. are separated by a filter 6 from channels lying below 31 kc/sec. It is concerned with impedance-matching designed to reduce cross-talk arising from reflection of the higher frequencies at the ends of the line. The section E is designed for a standard length of 125 ft. of cable LC whose capacity of 585 micromicrofarads forms one shunt arm of this section. For matching shorter lengths of cable a shunt condenser CA and a series air-core variometer L are adjusted to build out the inductance and capacity of the cable. The impedance of the filter is matched by an additional adjustable unit 5 in combination with a further shunt condenser CB for lead-in cables of intermediate length (up to 150 ft.) the condensers CA, CB are set to different values so that the section E is asymmetrical. For long lead-in cables (up to 330 ft.) a fixed section G adapted to the impedance of the open-wire line OL is added between the cable LC and the line OL, and a fixed shunt condenser C'A may be added to the section E. The section E may be provided with calibrated dials.