The L3 Coaxial System: Quality Control Requirements

Economic solution of the equalization problem in the L3 system required limitation of the excursions of the transmission characteristics from the design center. To implement this, a pattern of distribution requirements for component elements of the system was worked out utilizing basic quality control techniques. An analysis of the several methods employed is presented with particular emphasis on the intent of the choices which were made and the operating characteristics of the resulting procedures. One of the novel features is the three-cell selection method which insures that the product delivered has the kind of distribution that is wanted even while the process is in trouble distribution-wise. 1.0 1.1 R E A S O N FOR R E Q U I R E M E N T S EQUALIZATION PROBLEMS The L3 system is a long distance carrier system designed to transmit either 1,860 telephone channels or 600 telephone channels plus one television channel. The band width is approximately 8 mc. The repeaters are spaced about 4 miles apart and in a 4,000-mile route, counting both line and office amplifiers there will be about 1,200 amplifiers in tandem. There are two equalization problems. The first is equalization proper, i.e., delivery of a satisfactory signal to the customer from the transmission characteristic point of view. The television equalization design objective of the system is to meet a signal-to-echo ratio of 40 db. This corresponds to a uniform sinusoidal ripple of 1/10 db or a complex deviation pattern several times larger in amplitude.