274 



BEI.L SYSTEM TI-.CI INICAL JOIH^NAL 



loading on No. 22-A.w.g. cable is (he preferred construction for 

 trunks from 7.5 to 11.5 miles long, when working to an 11-TU limit. 

 The lower part of Fig. 16 indicates on a cumulative-percentage basis 

 the distribution of direct interollfice trunk lengths in the Bell System. 

 In the design of the exchange area trunk plant, it is, of course, 

 necessary to consider the signaling characteristics of the facilities and 

 associated equipment, as well as the transmission characteristics. 



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TRUNK LENGTH-MILES 



Fig. 16 — Direct interoffice trunks 

 Field of use of different types of loaded and non-loaded facilities, working to 11 to 

 15 TU limits on attenuation loss. Curve in lower part of diagram shows distribu- 

 tion of trunks with respect to trunk length 



After a certain length is reached in a given type of facility, it may 

 become necessary to use relatively expensive signaling equipment 

 for working longer distances. In some cases of this kind, the total 

 facility cost may be reduced by using a more expensi^'e grade of 

 circuit which will allow less expensive signaling equipment. 



In the application of the new standard loading systems, the same 

 standards of over-all attenuation loss are adhered to, as in the older 

 loading systems. In consequence, there is an appreciable improve- 

 ment in the intelligibility of transmission, due to the ability of the 

 new loading systems to transmit efificiently a range of high frequency 

 v.,ice over-tones which are suppressed by the old standard 2,o0()- 

 c\cle cut-off. 



Along with this impro\-cment in ser\ice, the new loading systems 

 substantially reduce the plant cost; partly due to the economies 

 which result from the extension of the transmission range of the new 

 types of tine wire cables, and partly because of the use of materialK' 

 less expensive types of loading coils. 



