284 BELL SYSTEM TECHNICAL JOURNAL 



manual Morse operation outlined below, can be of material use as a 

 general guide. 



1. The effect of distortion upon accuracy of reception differs in 

 character for different types of distortion. For some types of distor- 

 tion the accuracy decreases rapidly when the distortion exceeds a 

 certain value, which indicates that there is a rather definite limiting 

 value of distortion. For other types of distortion, the accuracy of 

 reception decreases very little nearly up to the point where the circuit 

 actually fails. 



2. The amount of distortion which appears to be tolerable, both from 

 the standpoint of accuracy of reception and from the opinion of opera- 

 tors appears to be larger for combined distortions than for the indi- 

 vidual types of distortion. This would seem to indicate that the 

 maximum distortion by itself, without at least a general idea as to the 

 components making up the distortion, is not sufficient to indicate how 

 satisfactory the circuit will be for handling manual telegraph service. 



3. The effect of distortion upon the operators themselves, as indi- 

 cated by the errors which they made, appears to be such as to cause 

 hesitation and a resulting confusion while interpreting distorted signal 

 combinations. Most of the errors In the case of large distortions con- 

 sisted of miscellaneous interpretations with letters frequently added 

 or omitted. For some types of distortion, especially those for which 

 the accuracy of reception begins to decrease rapidly at a certain value 

 of distortion, consistent misinterpretations were made. These usually 

 occurred after the accuracy of reception had decreased appreciably, 

 and were of a nature such as would be expected from the type of 

 distortion present in the signals. 



4. The opinion of the operators as to the amount of distortion above 

 which a circuit is unsatisfactory for commercial operation, is in reason- 

 able agreement with the effect on their accuracy of reception for some 

 types of distortion ; for other types of distortion there is considerable 

 disagreement. In general, the operators pronounce a circuit un- 

 satisfactory before the point is reached where the accuracy of reception 

 decreases appreciably. 



The agreement which exists between the two criteria Is shown in the 

 following table. The values In the first column of the table are based 

 on the opinion of the operators, while those In the second column are 

 based on their accuracy of reception and are those values at which the 

 accuracy has decreased 2 per cent from the initial value. In every 

 case the value given is the average for all the tests made with a par- 

 ticular type of distortion. 



