The L5 Coaxial-Carrier Transmission System is a new solid-state broadband system designed to transmit 10,800 long-haul message channels on standard %-inch (9.5-mm) coaxial cable. Alternatively, high-speed digital signals may be transmitted in selected mastergroups. This paper contains an overall system description and describes in detail system design considerations such as the transmission plan, frequency allocation, and 4000-mile noise performance. Also considered are the significant proper ties of the coaxial medium, the ways they affect the hierarchy of equalizers traditionally found in long-haul coaxial systems, and the manner in which the several levels of equalization relate to each other and to the fundamental transmission phenomena within the system.
The equalizing and main station repeaters, together with the L‐4 control center and command looping circuits, provide for the equalization and remote fault location in the L‐4 system. The use of pre‐ and postequalization procedures requires virtually identical circuits at the sending and receiving main station repeaters, while abbreviated versions of the same equipment are placed in up to two line equalizing repeaters per main section. In most cases these equalizing stations occur at approximately every twenty‐fifth repeater in a completed system. The fault‐locating circuits are distributed over the entire system and the control circuits required for their activation are located at the equalizing points.
Repeatered line design for long-haul coaxial systems centers about the equalization of the 4000-mi (6400-km) cable loss. In the L5 system, which provides 10 800 toll grade quality message channels on a pair of 0.375-in (9.5-mm) coaxials, this loss is over 120 000 dB at the highest message frequencies and is compensated with a variety of fixed and adjustable equalizers distributed along the coaxial line. This equalization must be achieved while at the same time providing an adequate signal-to-noise ratio. The significant properties of the coaxial medium and how they affect the "hierarchy" of equalizers traditionally found in long-haul coaxial systems are described. The manner in which the various levels of equalization relate to each other and to the fundamental transmission phenomena within the system is considered at length. The paper begins with a discussion of the evolution of highcapacity systems and the particular role that the L5 system is expected to play in future long-haul system planning.
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