The L-4 Coaxial System

A new long-haul coaxial cable system, L-4, has been developed to transmit 3600 voice circuits on a pair of %-inch diameter coaxial cables using frequency division multiplexing. A field trial was held in Ohio and completed successfully in early 1967. The system was turned up for commercial service in October 1967 on a route between Miami, Florida, and Washington, D. C. The L-4 system is the latest in a family of long-haul coaxial systems. Each of the earlier systems was considered a large capacity system in its time. 1 , 2 With the rising need for circuits and the advances in technology, each succeeding system has had increased capacity, as shown in Table I. Since system costs are dominated by the cost of the installed coaxial medium, the more efficient use of the line by the later systems effectively reduces the cost per circuit-mile. The increased capacity of the L-4 system, plus the relatively low cost of the solid state transmission equipment, has made it possible to reduce the cost of coaxial circuits by a factor of three compared with the cost of L-3 circuits. In addition to its voice channel capacity, the principal features of the L-4 system are: 821