Some Theoretical and Practical Aspects of Noise Induction* 



By R. F. DAVIS and H. R. HUNTLEY 



This article discusses the physical processes of induction between neigh- 

 boring power and telephone lines and describes means by which certain phe- 

 nomena of interest in this connection have been qualitatively demonstrated 

 to power and telephone employees. 



Introduction 



T? ARLY in the development of the power and telephone industries, 

 •L' serious problems were encountered because of induction between 

 neighboring power and telephone circuits. In 1885, about 150 repre- 

 sentatives of Electric Light Companies assembled in Chicago and dis- 

 cussed the many problems of interference with telephone service due 

 to induction which were even then coming up. This meeting resulted 

 in the formation of the National Electric Light Association. 



Prior to this time all telephone circuits were grounded, that is, they 

 used a single wire with ground return, and so were very susceptive to 

 inductive disturbances. There was also a great deal of interference 

 between different telephone circuits on the same line (that is, cross- 

 talk) so that conversations on one circuit could be overheard on others. 

 General John J. Carty, then working in Boston, had been doing a great 

 deal of work on this subject and by about the end of 1885 had not only 

 developed the metallic telephone circuit, which employs two wires and 

 does not use the earth as part of the circuit, but also had worked out 

 methods of applying transpositions. These developments afforded 

 such a large reduction in the susceptiveness of the circuits to external 

 influences that the problems of coordination existing at that time were 

 largely solved. 



However, with the expansion and development of the power and 



telephone industries, new problems of coordination arose, and the 



nature and control of the phenomena involved have been the subject of 



continuous study by both industries. While a great deal has been 



learned about the technical phases of the problem and the best methods 



of handling it, the coordination of the plants of power and telephone 



companies in such a way that safety and service are promoted with 



minimum expense still involves important problems. These problems 



not only concern the engineers who are responsible for plant design and 



for technical advice, but also enter into the work of the field forces who 



* This paper appeared in somewhat different form in Amer. Railway Assoc. Proc, 

 June, 1932, under the title "Demonstration and Talk on Noise Induction" by 

 H. R. Huntley. 



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