Publication: Western Electrician
Chicago, IL, United States
Pupin Telephone Load Coils.
Mention has already been made in these columns of the experiments conducted on telephone circuits near Berlin, Germany, to determine the advantages of applying to the lines the inductance or load coils which have been invented by Professor M. I. Pupin and which are used in this country by the American Telephone and Telegraph Company. The Germany experiments showed that by the application of Pupin's system, an underground cable with a conductor of one millimeter diameter could be rendered equivalent in speaking capacity to an ordinary unequipped overhead wire of two millimeters diameter, or four times the section. The arrangement of the inductance coils was very simple. Each set of 14 coils of annular construction was inserted in an iron box, and the necessary connections to the cable made by means of a special connection box, both being subsequently filled up with compound. Fig. 1 gives a view of such a box with the connections complete.
The coils were inserted in the underground cable at an average