Effect of Signal Distortion on Morse Telegraph Transmission Quality

W H E N E V E R 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 transmission. 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 development 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 keyboard and received so as to cause the selection and printing of the proper character by mechanical means.