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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



ities. This means of course that all the functional characteristics of the set 

 must realize this objective. If, for example, extended range of transmission 

 were not accompanied by a corresponding increase in dialing and ringing 

 range, the entire potential value would not be reaHzed. 



A second objective was to reduce the transmission variations now experi- 

 enced between individual users, and between the station most distant and 

 that nearest the central office. A related objective of minimizing the variety 

 of sets needed suggested the desirability of combining in one set, in so far 

 as was economic, the required number of circuit arrangements to satisfy 

 individual, party line, and measured service. 



DIAL 



EQUALIZER 



Fig. 3 — Circuit schematic of 500-set. 



There was, of course, plenty of incentive to incorporate in the design 

 whatever experience had indicated might be done to retain or better the 

 excellent maintenance performance of the current standard combined set. 



With these general objectives in mind somewhat more detailed descrip- 

 tion of the circuit and design is in order. It will perhaps be somewhat clearer 

 to take up each of the main functions in turn and to show for each how the 

 specific objective was approached. It might be stated at this point that the 

 description is based of necessity on the design as it was in the early pro- 

 duction. The usual Bell System process is underway to find more economical 

 and reliable ways to accomplish the objectives. The characteristics described 

 herein will in general apply equally to any such modifications. 

 Transmission 



The general objective called for the maximum usable increase in transmit- 

 ting and receiving volume on long loops. This meant gains in each direction 



