THE BELL SYSTEM 



TECHNICAL JOURNAL 



VOLUME XXXII JULY 1953 numbbr4 



Copyright, 1953, American Telephone and Telegraph Company 



The L3 Coaxial System 



Foreword 



The articles in this issue are devoted to different phases of the develop- 

 ment of a new system for the transmission and utilization of broader fre- 

 quency bands on existing or new coaxial cables. This new system, which 

 is called the L3 carrier system, represents the latest phase of develop- 

 ment activities begun in the late twenties. It permits far more intensive 

 exploitation of the cable medium than its predecessor, affording the op- 

 tion of providing, in each direction on a pair of coaxial tubes, either 1860 

 telephone channels or 600 telephone channels and a 4.2 megacycle 

 broadcast television channel. 



These results have been attained through wide extension of previous 

 art. New electron tubes, transformers, inductors, and other circuit 

 elements have been designed for extreme precision in respect to stability 

 and other performance factors. Statistical quality control techniques 

 are being applied to obtain the benefits of closely controlled distribution 

 of the performance of circuit elements and system units. Fundamental 

 to the program has been the devising of techniques for achieving hitherto 

 unobtainable accuracies in the measurement of impedance, loss, phase 

 and other transmission properties. To provide precise attenuation and 

 delay characteristics over the wide frequency band, new techniques of 

 network synthesis have been developed. 



Refined system analysis and circuit design have derived maximum 

 performance from component capabilities. The highest standards of 



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