Some Theoretical and Practical Aspects of Noise Induction

E A R L Y in the development of the power and telephone industries, serious problems were encountered because of induction between neighboring power and telephone circuits. In 1885, about 150 representatives of Electric Light Companies assembled in Chicago and discussed 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, crosstalk) 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.