Effect of Signal Distortion on Morse Telegraph 

 Transmission Quality 



By J. HERMAN 



In applying telegraph transmission measuring apparatus to the develop- 

 ment and maintenance of telegraph circuits, it is desirable "to correlate 

 quantitative measurements of telegraph signal distortion with quality of 

 telegraph transmission. Accordingly, a series of tests has been carried 

 out in order to determine this relationship for the case of manual opera- 

 tion using the American Morse Code. These tests are described and the 

 results, together with the conclusions reached, are given in summarized 

 form. 



I. Introduction 



WHENEVER telegraph signals are transmitted over a circuit 

 they become more or less distorted depending upon the type 

 of circuit, the adjustment of the apparatus and the speed of trans- 

 mission. An adequate knowledge of the relationship between the 

 possible types of distortion and the satisfactoriness of the telegraph 

 services rendered over various circuits is evidently of considerable 

 importance. This is true both in the design of telegraph circuits to 

 insure the necessary quality of transmission and in the operation and 

 maintenance of these circuits to insure that they are giving the service 

 for which they are designed. 



Considerable data both qualitative and quantitative, bearing on 

 this matter have been collected in the past in connection with develop- 

 ment work and as a result of operating experience in the Bell System. 

 Recently some tests were made to correlate quality of telegraph 

 transmission with quantitative measurements of signal distortion on 

 manual telegraph circuits employing the American Morse code. This 

 paper presents and discusses the results of these tests. 



Commercial telegraph operation over land lines in the United States, 

 is carried on almost exclusively by two well known methods, manual 

 Morse and printing telegraph. In the first method, the signals are 

 sent by hand in accordance with the Morse code and received by ear 

 by listening to the clicking of a sounder. In the second method, the 

 signals are sent mechanically under the control of a typewriter key- 

 board and received so as to cause the selection and printing of the 

 proper character by mechanical means. Although the question of 

 permissible distortion in transmission is of importance for both 

 methods, it is to be expected that the answer will be considerably 

 more involved for the manual Morse case since the human element is 

 so large a factor in this case. 



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