The L3 Coaxial System: System Design

The L3 coaxial carrier system is a new broadband transmission system capable of transmitting either 1,860 telephone message channels or 000 message channels and a 4.2-megacycle broadcast television channel, in each direction, on a pair of coaxials. The system is designed so that signals- transmitted over any of these channels will meet high quality Bell System objectives after 4,000 miles of transmission. The system is composed of auxiliary or line repeaters spaced at approximately four-mile intervals along the cable route and connecting terminal or dropping repeaters where telephone or television signals are translated to or from the L3 frequency band. Equalization equipment, power generating and power transmission equipment, and maintenance equipment are required at 100 to 200-mile intervals. Planning and exploratory development for the system was started late in 1945 with the objective of designing a trunk route system which would provide the maximum channel capacity on the existing coaxial cable consistent with the state of the repeater art. At that time and for the next four years a large amount of new cable employing the G O O channel-three megacycle LI coaxial carrier system was being installed or projected. 1 Since a major field of use of the L3 system was to replace the LI 781