LOADING I-'OR lliLIiPI lOKP. CIRCUITS 



273 



In general, it will be noled from Table X\T thai the facility cost 

 is in re\erse order to the transmission efficiencN'. However, there are 

 exceptions to this general tendency- : for instance, non-loaded No. 19- 

 A.w.g. cable is less efficient ar.d more expensive than No. 22-A.w.g. 



0.40 



500 1000 1500 2000 2500 3000 



FREQUENCY-CYCLES 



Fig. 15 — Attenuation-frequency characteristics of typical exchange area loaded and 



non-loaded cables 



cable with M-88 or H-135 loading. From this it will be apparent 

 that non-loaded No. 19-A.w^g. cable has practically no economical 

 field of ser\-ice on a competitive basis wath loaded No. 22-A.w.g. cable. 



The problem of the plant engineer in laying out trunk cables is to 

 determine for each trunk group the type of facility w'hich will meet the 

 established transmission standards with the lowest cost. The permis- 

 sible loss in a given length of trunk in a particular area depends on 

 the type of service involved; for instance, a larger loss is allowable 

 in a direct interoffice trunk than in other types of trunks forming 

 part of a toll connection. 



The allowable loss for a given length and type of trunk varies 

 widely among different metropolitan areas, due to local conditions. 

 These limits are established by means of "loop-and-trunk" studies 

 which determine for a particular area the most economical allocation 

 of the permissible over-all loss between the subscriber loops and the 

 interoffice trunks. On account of the wide range of local conditions 

 the fields of service of the different types of loaded and non-loaded 

 trunks cannot be sharply defined. An indication of the service uses 

 is given in the upper part of Fig. 16, which illustrates the possible 

 applications of the new standard types of facilities for direct inter- 

 office trunk service, assuming maximum allowable losses of 11 and 

 15 TU, respectively. The diagram shows, for instance, that M-88 



