Recent Developments in the Measurement of 

 Telegraph Transmission 



By R. B. SHANCK, F. A. COWAN and S. I. CORY 



This paper describes the progress which has been made in re- 

 cent years in the development of methods and apparatus for the 

 measurement of telegraph transmission in the Bell System. Such 

 measurements pla^^ an important part in transmission maintenance 

 work in the field and are also necessary in development work. The 

 changes which have occurred in service requirements, particularly 

 the large commercial development of start-stop teletypewriter serv- 

 ice and the effect of these changes on the technique of telegraph 

 transmission measurement, are first discussed; then a description is 

 given of several new measuring devices and their use. 



TN keeping with advances in the telegraph transmission art, note- 

 -'- worthy improvement has been made in measuring devices and 

 methods in the past few years. The faster, more accurate, and 

 generally more dependable telegraph service now available has been 

 made practicable not only by improvements in the telegraph systems 

 but also by the use of improved measuring apparatus and techniques. 



In the early stages of development most transmission-measuring 

 systems were arranged to measure transmission on "looped" circuits, 

 that is, with sending and receiving terminals at the same point, so 

 that a comparison between the sent and received signals could be made. 

 Although such an arrangement is quite useful for laboratory testing, 

 it imposes serious limitations on field testing. Therefore, it is generally 

 desirable to make tests on a straightaway basis. 



For straightaway tests it is necessary to have at the receiving end 

 certain information regarding the sent signals. This requires either 

 the use of signals of certain known characteristics or the determina- 

 tion of the important characteristics of the sent signals and the trans- 

 mission of this knowledge to the receiving end. The latter of these 

 alternatives is not frequently used since it requires another com- 

 munication channel, although in some instances, where tests on 

 working circuits are desired, it represents the only practicable ap- 

 proach. Straightaway measurements of telegraph transmission have 

 for this reason been generally confined to measurements in which the 

 important characteristics of the transmitted signals were known. 



Fortunately, either synchronous or stop-start teletypewriter signals 



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