The L3 Coaxial System 



Quality Control Requirements 



By H. F. DODGE, B. J. KINSBURG and M. K. KRUGER 



(Manuscript received May 5, 1953) 



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 Reason for Requirements 



1.1 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 tele- 

 vision channel. The band mdth 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 transmis- 

 sion 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. The telephone equal- 

 ization objective is more lenient and allows deviations as large as 1 to 

 2.5 db, depending on length of circuit and number of links in tandem. 

 Though care was exercised to make basic design decisions which would 

 tend to ease the equalization problem, still the reduction of the accumu- 



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