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BELL SYSTEM TECHNICAL JOURNAL 



of transmitters and receivers and of variation of sidetone in the station 

 set. In addition to the observations of repetitions, measurements are 

 made of the talking levels on the trunks by means of volume indicators 

 to determine the reaction of the circuit performance on talking levels. 



An illustration of the results of such observation is given in Fig. 1. 

 The curve shows the variation of the repetition rate with change in 

 trunk attenuation for connections having the same kinds of terminal 

 sets and loops at both ends. This then provides a means of expressing 

 different grades of service performance in terms of trunk attenuation in 

 this circuit. 



On this figure is shown also the repetition rate obtained for trunks of 

 two different effective upper cutoff frequencies. The change in trunk 



30 



5 10 15 20 25 



TRUNK EQUIVALENT AT 1000 CYCLES 



Fig. 1— Relation between repetition rate and trunk equi\alent 



attenuation required to produce the same increase in repetition rate as 

 that obtained in going to point C, for example, from the corresponding 

 1,000-cycle attenuation point on Curve A , is taken as the rating in db of 

 the lower cutoff' frequency represented by point C. This rating is 

 about 5 db. The rating of point B with respect to A is obtained in a 

 like manner to be about 1 db and correspondingly the rating of the cut- 

 off frequency of C with respect to B is about 4 db. This illustrates the 

 manner of obtaining effective transmission ratings for any change from 

 the characteristics of the circuit of Curve A. 



It is obviously laborious to cover the ranges of all the transmission 

 characteristics of circuits of this kind. The idea is to establish points 

 which will cover the practical range and to use the results of articulation 



