A Magneto-Elastic Source of Noise in Steel Telephone Wires

' I ^HERE probably are few persons who have not had the experience of standing near some telephone or telegraph line out in the open and hearing the singing of the wires resulting from the wind blowing over them. Perhaps in childhood it was a source of wonderment why these sounds could not be heard at the telephones, and later, upon learning that telephone transmission was accomplished electrically and that these vibrations were mechanical only, tolerant amusement was felt at this earlier ingenuousness. Apparently it has remained until a very recent date for the discovery unmistakably to be made that it is possible under certain conditions for the mechanical vibration of a telephone wire to generate electromotive forces of sufficient magnitude to become objectionably audible in the telephone circuit. It was in April, 1935 that Mr. G. G. Jones of the Long Lines Department of the American Telephone and Telegraph Company mentioned to one of the writers the experience his Company had had a short time before in tracing down a supposed case of inductive noise to the action of the wind upon a 1200-foot steel-wire river-crossing span near Topeka, Kansas. This particular case had been cleared promptly by the application of suitable vibration damping devices generally recommended for situations where vibration might cause trouble. Special investigations then were made of long steel-wire spans at several locations in the Southwestern Bell Telephone Company territory, and it was revealed that some slight noise derived from this source actually was present in every case--and in one particular instance, where the wind velocity and direction happened to become very favorable to the production of wire vibration during the time of the inspection, the noise arose to a serious magnitude.