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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



the improved loading. A brief general discussion of this particular advantage 

 is given in subdivision 20.3. 



The field of use of the new loading systems on exchange area trunks in- 

 volves a number of factors, the most important being the cable length and 

 gauge, the subscriber-loop limits, and the transmission equivalent desired. 



The B spaced loading is required principally on long toll connecting 

 trunks and tandem office facilities and has some use on the longest direct 

 inter-office trunks. For plant simplicity and fiexibiUty reasons, both types 

 of B spaced loading are seldom used extensively in the same exchange 



Table XII 

 Improved Loading Systems Standardized in 1932 



Table XIII 

 Attenuation Data— Loading Systems of Table XII 



area. B135 loading is more likely to be used in large metropoUtan areas, and 

 B88 loading in smaller multi-office areas. 



The H88 loading is used in all multi-office areas that have direct trunks 

 long enough to require loading. In such use it supersedes the former standard 

 M88 loading in new plant, and partly supersedes the former standard heav- 

 ier-weight loading systems, H135 and H175. 



It was of great practical importance that the coil inductances used by the 

 improved loading systems should be those of available standard coils and 

 of extensively used former standard coils, so as to faciUtate the rearrange- 

 ment and conversion of the old loaded plant to meet the new transmission 

 standards. In this general connection, the exchange cable trunk plant must 

 be more or less continuously fluid for several important reasons, including 

 the following: (1) to accommodate the traffic growth along existing routes 



