The L3 Coaxial System: Television Terminals

The main features of the L3 coaxial cable transmission system have been described in a companion paper.1 This paper describes the television transmitting and receiving terminal equipment of the L3 system. The 915 916 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1 9 5 3 transmitting terminal conditions a television signal for carrier transmission over the system simultaneously with a group of 600 telephone messages. The receiving terminal reconverts the carrier signal at each receiving point along the cable route. Primarily, the transmitting terminal is a modulator which translates the composite video picture spectrum of frequencies up to the carrier band of frequencies and the receiving terminal is a detector which retranslates the carrier spectrum back to its original band of frequencies. Particular characteristics of the transmitted television signal, which are intended to aid in achieving optimum transmission quality, have necessitated the departures from past techniques in modulation and demodulation processes that are described in the following. Described also are the methods employed to achieve transmitted picture quality adequate for tandem operation of as many as six pairs of transmitting and receiving terminal equipments in a 4,000-mile television transmission circuit. Operation with several pairs of terminals in tandem occurs when L3 coaxial systems are interconnected with LI coaxial systems or microwave radio systems. L3 television terminal development has been in progress since early in 1948.