Line Problems in the Development of the Twelve-Channel Open-Wire Carrier System

A N E W carrier telephone system for open-wire telephone lines has been described recently. 1 This system increases the number of two-way telephone circuits which can be obtained on a single pair of wires from the previous maximum of 4 to a total of 16. T h i s has been achieved by extending the frequency range from a maximum of a b o u t 30 kilocycles to more than 140 kilocycles. T h e exploitation of this new range of frequencies on open wire has involved the solution of a n u m b e r of interesting problems, among which are these: (1) N o t only does the attenuation of an open-wire line under ordinary weather conditions rise substantially with frequency but extremely large increases in attenuation occur at the higher frequencies when ice forms on the wires. 1 -* In spite of these effects a high degree of stability of transmission has been secured on all channels by the provision of a u t o m a t i c control of repeater gain and equalization. (2) New crosstalk problems created by the extension of the frequency range have been solved by t h e development of transposition designs with numbers of transpositions not greatly in excess of those employed for the lower frequency systems. Problems have also arisen in controlling the crosstalk around the repeaters and in reducing the effect of impedance departures between the line circuits and the equipment. FREQUENCY ALLOCATIONS