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BELL SYSTEM TECHNICAL JOURNAL 



unchanged up to a distortion of about 75 per cent and decreased 

 slowly for distortions above this value. The operators first remarked 

 upon the distortion at a value of about 35 per cent and considered the 

 circuit unsatisfactory at about 50 per cent. 



100 



96 



o 9i 



68 



64 



80 



'0 20 30 40 50 60 70 80 



Per Cent Oistorbion 



Fig. 6. 



5. Effect of Combined Distortions 



A large number of tests were made with various combinations of 

 distortions, the results of which were also plotted in the form of curves. 

 These curves are not included here because of lack of space but the 

 results obtained are discussed below. 



The maximum permissible distortion is generally much higher when 

 the distortion occurs in combinations of various kinds than when it 

 occurs singly. This is true when judged either from the standpoint of 

 accuracy of reception or opinion of operators. Moreover, it appears 

 that the shape of the distortion versus accuracy curve is determined 

 largely by the predominating type of distortion. 



It would seem from the above that a measurement of maximum 

 distortion only, is not sufficient to determine the condition of a tele- 

 graph circuit. For example, a circuit may have a maximum distortion 

 of about 50 per cent. If this is made up of 35 per cent negative char- 

 acteristic distortion and 15 per cent fortuitous distortion the circuit 

 would be considered very poor by the operators. If, however, it were 

 made up of 15 per cent negative characteristic distortion and 35 per 

 cent fortuitous distortion, the circuit would be considered fairly good. 

 Similar deductions can be drawn from other combinations of distortion. 



