EFFECT OF SIGNAL DISTORTION IN MORSE TELEGRAPHY 277 



2. Effect of Bias 



A . Positive Bias. — The relationship between the amount of positive 

 bias and the accuracy of reception by operators is given in Fig. 2, 

 in which is plotted the average of the results obtained in three tests. 



It will be seen from an inspection of this curve that the accuracy 

 falls off rapidly between 40 per cent and 50 per cent bias in which 

 region the majority of the operators also called the circuit unsatis- 



96 



R 86 



«. 84 



80 



76 



10 20 30 40 SO 60 70 60 



Per Cent Distortion 



Fig. 2. 



factory. The three most interesting facts, as depicted on this curve, 

 are as follows: The accuracy of reception changed very little up to a 

 bias of about 40 per cent but decreased rapidly above this value. The 

 operators remarked upon the bias when it reached a value of about 

 20 per cent, and considered the circuit unsatisfactory with a bias of 

 about 40 per cent. 



An analysis of the errors made by the operators for values of bias 

 from 35 per cent to 70 per cent showed that most of the errors were 

 due to the omission of letters. This indicates that the effect of positive 

 bias was such as to confuse the operators and cause them to miss 

 characters while trying to interpret some peculiar sounding character 

 which had gone before. There was very little indication of errors due 

 to interpretations of dots as dashes even for a bias greater than 50 per 

 cent. Most of the interpretations were of a miscellaneous nature, 

 although there were a few errors which appeared to be due to a dropping 

 out of spaces between signal elements. 



