Sydney-Melbourne type J carrier telephone system

This system, already described [Abstract 1939B01196], provides 12 channels on a single pair of wires in addition to 3 already derived from a type C system and the normal voice-frequency circuit. After a reacutesumeacute of the features of the J system, the authors deal with its application in Australia. One system was initially installed using existing offices as repeater stations, the longest repeater section being 78 mi. and the shortest 33 mi. Line attenuation is considered, and the results of measurements up to 140 kc./s., the highest frequency transmitted, are given. Dry and wet weather losses are included. Cross-talk considerations were not acute, as only 1 pair was used, but were complicated by near-end cross-talk between the "in" and "out" pairs from the main route to the stations. Means of dealing with this problem are described. The lead-in cables were disc-spaced, air-dielectric star quads, the low-capacitance pairs being readily matched by loading to the impedance of the open-wire line. Diagrams of overall transmission levels and loss/frequency characteristics and an account of testing and maintenance routine are included.