JOINT DEVELOPMENT AND NOISE FREQUENCY INDUCTION 185 



frequency and low-frequency problems brought about by the close 

 proximity of the two types of service when occupying the same poles. 



The Joint Subcommittee on Development and Research has sub- 

 divided its work among ele\en project committees and assigned to 

 each the actual carrying on of specific research work. Certain of the 

 project committees are engaged on the problems described in this 

 paper, while the remainder are concerned with the development and 

 research problems of the companion papers, Parts III and IV of the 

 Symposium. The names of these project committees, together with 

 a statement of the phase of the problem considered by each, is given in 

 Volume I of "Engineering Reports of the Joint Subcommittee on 

 Development and Research." ^ 



Naturally the first steps taken by the Joint Subcommittee were the 

 review and appraisal of existing information and the exchange of data 

 between the two interests represented. This paper includes a state- 

 ment of the problem, with some review of the factors involved, the 

 results accomplished by the subcommittee and the work projected in 

 connection with each factor. 



Classification of Factors Contributing to Induction 



There are certain characteristics of a power circuit with its associated 

 apparatus that determine the character and intensity of the electric or 

 magnetic field which is set up in the surrounding medium. These 

 characteristics are termed "Influence Factors." - 



Likewise, there are certain characteristics of a communication cir- 

 cuit with its associated apparatus which determine its responsiveness 

 to external electric or magnetic fields. These characteristics are 

 termed its " Susceptiveness Factors." - 



There is a third group of factors which refer to the interrelation of 

 neighboring power and communication lines by electric or magnetic 

 induction or both. These are termed "Coupling Factors."'^ 



Inductive interference is thus the manifestation in the telephone 

 circuit of a combination of influence, susceptiveness and coupling; and 

 inductive coordination consists in the control of factors in all three of 

 these classes to the degree required for satisfactory operation of both 

 services. 



Methods of Control 



Physical Separation . — The first method which comes to mind for the 

 control of inductive eft'ects is that of physical separation obtained by 

 placing the power and telephone lines on separate routes. A separation 



> For references see bibliography. 



