EFFECT OF SIGNAL DISTORTION IN MORSE TELEGRAPHY 275 



III. Discussion of Results 

 1 . General Effect of Distortion 



A. Effect Upon Accuracy of Reception. — ^The effect of distortion 

 upon accuracy of reception, as shown by the results of the tests, differs 

 in character for different types of distortion. In accordance with the 

 effects produced, the various types of distortion may be divided into 

 two general classes. The first class consists of types of distortion which 

 produce only a small change in the accuracy of reception nearly up to 

 the point where the circuit actually fails. The second class consists 

 of types of distortion which produce a rapid decrease in accuracy of 

 reception when the distortion is increased beyond a certain moderate 

 value. Of the various types of distortion encountered on telegraph 

 circuits, negative bias and fortuitous distortion fall into the first class 

 while positive bias and positive and negative characteristic distortion 

 fall into the second class. 



Combinations of various types of distortion in which one type of 

 distortion predominates appear generally to fall into the same class 

 as the predominating type of distortion in the combination. There is, 

 however, a marked tendency for many combinations of distortion to 

 fall into the first class, especially, when the various distortions in a 

 combination are about equal in magnitude. 



The accuracy of reception for a particular circuit condition differed 

 considerably with operators. For the case of zero distortion in a 

 circuit, most of the operators consistently reached accuracies between 

 98 and 100 per cent while other operators failed to reach accuracies 

 higher than 88 per cent. This difference is due partly to the fact that 

 some of the receiving operators were more experienced than others and 

 partly to poor sending by some of the sending operators. It is of 

 interest, however, that the general shape of the distortion versus 

 accuracy curve for a given condition is unaffected by this difference. 



B. Effect Upon Opinion of Operators. — ^In general, the various 

 operators were in fair agreement as to the point at which a circuit 

 became unsatisfactory for commercial operation. This point corre- 

 sponded closely with the decrease in accuracy of reception for some 

 types of distortion but differed widely from it for other types of distor- 

 tion. In those cases for which the opinion of operators disagreed with 

 their accuracy of reception, the operators usually pronounced the 

 circuit unsatisfactory at values of distortion considerably lower than 

 those required to cause an appreciable decrease in their accuracy of 

 reception. The reason given for condemning such a circuit at the low 

 value of distortion was the peculiar sound of the signals. This, they 



