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BELL SYSTEM TECHNICAL JOURNAL 



on the type and length of the subscriber loop. This is exactly the 

 method used in the volume data where its use followed logically from 

 the mathematics which give the loss of a line at a single frequency. 

 The use of this method with effective data is permissible only because 

 the effects of trunk distortion as well as volume loss can be treated, 

 with a satisfactory degree of approximation, as a linear function. 



The trunk loss per unit length equals the slope of the curves and 

 can be defined, therefore, as the increase in effective loss per mile 

 increase in length of a trunk, which is initially electrically long, when 

 used between the reference loops. In the case of loaded trunks, this 

 increase in length must be accomplished without change in end sec- 

 tion. The trunk loss per unit length, although measured between the 

 reference loops, can be treated as independent of loop. It includes 

 two component losses, the volume loss per unit length, and the effect 

 of the increase in distortion per unit length. 



Effective terminal junction losses are corrections associated with 

 the junction of a loop and trunk which are added in computing the 

 effective equivalent of a circuit employing a trunk other than the 

 reference trunk. For a circuit with two equal loops each loss equals 

 one-half the Y intercept in Fig. 4. It is dependent on the type of set, 

 the type and length of loop and on the type of trunk but is independent 

 of trunk length. It contains a volume reflection correction, the effects 

 of that part of the trunk distortion which is independent of length, 

 and the effects of trunk impedance on sidetone. Fig. 5 is a sample of 

 the form in which these losses are presented. 



2 



3 

 4 



10 15 20 



LOOP LENGTH IN 1000 FEET 



Fig. 5 — Effective terminal junction loss. 



30 



The central office losses present data relative to the loss of central 

 office apparatus and cabling other than that included in the loop 

 losses. They are determined by substituting the apparatus to be 

 rated for the corresponding parts of the working reference system, and 

 equal the effective loss of this condition relative to the working refer- 



