EFFECT OF SIGNAL DISTORTION IN MORSE TELEGRAPHY 283 



There was also some indication that a circuit which contains an 

 appreciable amount of one type of distortion may be improved by 

 adding a certain amount of some other type of distortion, even though 

 the total distortion is increased thereby. This was brought out in a 

 certain test where 25 per cent negative characteristic distortion by it- 

 self made the circuit unsatisfactory. By adding 15 or 20 per cent 

 positive bias the quality of the signals was improved, as shown by the 

 accuracy of reception and by the opinion of the operators, even though 

 the maximum distortion was increased from 25 per cent to 40 or 45 

 per cent. 



The nature of the errors made by operators for combined distortions 

 in the circuit varied greatly for different combinations of distortion. 

 Positive bias combined with moderate amounts of negative character- 

 istic distortion gave errors similar to those for negative characteristic 

 distortion alone. On the other hand negative bias combined with 

 moderate amounts of negative characteristic distortion gave errors of 

 a miscellaneous nature, such as were obtained with negative bias alone. 

 Combinations of fortuitous distortion with moderate amounts of 

 positive bias gave errors which indicated a consistent lengthening of 

 marks and dropping out of spaces, as for example, interpretations of 

 A as M ; N as T and J as K. Combinations of fortuitous distortion 

 with negative bias, however, gave errors which were chiefly of a 

 miscellaneous nature. In addition to the above there was an ap- 

 preciable number of letters added and omitted for all combinations of 

 distortion. 



A brief summary of the effects of combined distortion upon recep- 

 tion is as follows. The curves of accuracy versus distortion have the 

 same general shape as the curves for the predominating type of dis- 

 tortion taken by itself, and the maximum permissible distortion, as 

 judged either by the accuracy of reception, or by the opinion of the 

 operators, is generally higher than for the various combined distortions 

 taken by themselves. The values of total distortion at which the 

 accuracy of reception began to decrease, ranged from about 55 to 

 100 per cent. The operators considered the circuits unsatisfactory at 

 values of distortion ranging from about 50 to 65 per cent. 



IV. Summary 



There are given below conclusions which have been drawn tentatively 

 from the results of the present tests. Further tests are desirable in 

 order to confirm the results obtained thus far. For the present, 

 however, it is thought that the ideas as to the effect of distortion upon 



