A Twelve-Channel Carrier Telephone System for Open-Wire Lines

A R E wires supported on insulators, stretched between poles, make up the pioneer electrical communication circuit, the openwire line. Although great advances have been made in the application of cable structures, the open-wire lines still hold their own in some sections of the country. This is because, to offset their physical vulnerability, they have several unique virtues. They are flexible and permit adding one pair of wires at a time. They are also comparatively economical where conditions favor their use. Furthermore, they are low-attenuation circuits and for this reason were the first to be used for high-frequency carrier systems. The first carrier systems, beginning in 1918, added three or four channels to the existing voice circuit on a pair. To keep pace with this development, improvements in transposition systems were devised so that many such carrier systems might be operated on the same pole line. Such carrier systems, typified by the three-channel type C 1 system, have seen continuous growth in use in the long distance plant. Now a twelve-channel system, the type J, is being made 1 " C a r r i e r Systems on L o n g Distance Telephone Lines," H. A. Affel, C. S. Demarest and C. W. Green, Bell System Technical Journal, J u l y 1928, a n d A. I. E. E. Transactions, Oct. 1928, pp. 1360-1387. "A New Three-Channel Carrier Telephone S y s t e m , " J. T. O'Leary, E. C. Blessing a n d J. W. Beyer, Bell System Technical Journal, this issue.