1228 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



The use of electroplated loading as a substitute for coil loading on toll 

 cables, or on incidental cables in open-wire lines, did not appear to be 

 attractive when the cost estimates and the complex requirements on circuit 

 balance, stability, non-Unear distortion and flexibility were taken into 

 account. 



Summary 



Enough has been told in the preceding pages to support the earlier 

 statements regarding the low importance of continuous loading in the 

 growth of the Bell System, relative to that of coil loading. Obviously, the 

 success attained by the intensive development and in the very extensive 

 use of economical types of coil loading is an important factor in this situa- 

 tion. That these extent-of-use relations are not due to a lack of interest in 

 continuous loading is well demonstrated by the Bell System initiative in 

 developing the permalloy continuous loading that made high-speed telegraphy 

 practicable in long submarine telegraph cables, and by the other develop- 

 ment work summarized in this review. 



PART VII: EXTENT OF USE AND ECONOMIC SIGNIFICANCE 



Introduction 



Up to now, this account of coil loading has been in terms of individual 

 developments and their significance with respect to the prior art and current 

 developments in related fields, with occasional information regarding their 

 importance and extent of use. 



It is now appropriate to supply and analyze some general statistics 

 regarding the total amount of loading which has been used, in a rough 

 appraisal of the importance of coil loading in the growth of the BeU Tele- 

 phone System. Some important qualifications of the statistics are com- 

 mented upon in advance of the presentation of actual figures. 



The statistics here given and discussed are for the most extensive and 

 most important applications of coil loading, namely, for voice-frequency 

 loading over cable circuits. They are grouped in two principal categories: 

 (1) non-phantom type coils used on non-quadded exchange area cables, and 

 to a relatively very small extent on toll cables, and (2) side circuit and 

 associated phantom coils used on quadded long-distance and interurban toll 

 cables, and to a relatively very small extent on entrance cables in open- 

 wire lines and on long quadded exchange cables. 



The figures used are based on production statistics up to the end of 1949. 

 The important significance of the production figures is that they measure 

 at the time of manufacture the current demands for additional loaded 

 facilities required by the growth of the telephone system, and the up-to- 



