270 



BELL SYSTEM TECHNICAL JOURNAL 



per minute. This resulted from the unintelHgible nature of the text 

 which required a wider and more careful spacing of letters and words 

 than would have been the case with a more intelligible text. 



For measuring telegraph transmission, the methods outlined in the 

 paper referred to previously were used. A distortion measuring device 

 which measured total distortion and the components separately, and 

 which employed test signals known from past experience to be repre- 

 sentative and suitable for obtaining good data on telegraph trans- 

 mission, was provided. A speed of transmission of 15 d.p.s. was 

 chosen for the test signals in order that the data obtained could be 

 directly compared with distortions as measured in development work 

 and in field transmission measurements. Consequently, the results of 

 the tests could be made of immediate practical utility. 



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Fig. 1 — Diagram of Test Circuit. 



2. Test Circuit 



A diagram of the test circuit is shown in Fig. 1. The telegraph 

 circuit consisted of two artificial lines connected by a repeating relay 

 and arranged to transmit in one direction only. 



The sending operator transmitted into a local circuit at the point 

 marked "sending station." This local circuit could also be connected 

 to the source of standard signals which consisted of a distributor oper- 

 ated at a constant speed by means of a "phonic-wheel" motor. 



Signals sent into the local circuit operated a sounder, a polar trans- 



