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DELL SYSTEM TECHSICAL JOURNAL 



of loll circuits iind in locating and clearing any transmission troubles 

 which occur in service. Tests are made either liy looping two circuits 

 together at the distant terminals and measuring the loop loss or by 

 testing single circuits straight-away between toll centers equipped 

 with measuring instruments of this t\pe. 



In general, transmission testing apparatus (juickly locates kinds of 

 troubles which cannot be readily detected by other routine testing 

 methods. Transmission tests also ser\'e as a means for checking 



geniTal maintiMiancc ((indilions and for injuring that other routine 

 testing work is carried (Ui in an effective ni.iniur. 



As an illustration of the effect of some of the kinds of trouiilo 

 which transmission tests detect, Fig. 28 shows the transmission circuit 

 arrangement for a t\pical toll connection and below transmission 

 level diagrams are given for the normal transmission condition and for 

 conditions where common kinds of troidiles are present. The le\i-l 

 diagrams show how I lie normal overall transmission e(|uivalent is 

 increased when oiU' or a number of transmission troubles are present 

 in the various circuits going to make up the connection between sub- 

 scribers. As indicated some troubles are more severe than others. 



