Abstract
THE working of telephones is often seriously impaired by the noise due to induction from neighbouring power or railway lines. This problem has been closely studied by electrical engineers for the last thirty years. In a paper communicated to the Institution of Electrical Engineers on November 23, Mr. W. G. Radley and Dr. S. Whitehead show that rapid progress has been made in the solution of the problem during the last few years. The amount of the interference in any given case can now be determined quite definitely by mathematics. It is due both to electromagnetic and electrostatic induction and also in some cases to radio effects. The loss in the ‘articulation’ of a telephone depends on the frequency of the disturbing voltage. For example, to produce the same loss in articulation by means of a note having a frequency of 150 as a note having a frequency of 1050, at which the maximum disturbance occurs, the induced voltage would have to be increased 158 times (22 decibels). The Post Office has now made a ‘noise’ meter which gives at one reading the magnitude of the interference factor produced by all the induced harmonics. It is a great step in helping the electrical industry to know that interference with existing telephone systems by any projected power or railway scheme can now be predetermined in advance. If it is too great, it can be decreased by a suitable choice of generators, the use of power cables or telephone cables instead of overhead circuits, etc. When there is a short circuit on the power line, and there are large transitory earth currents, there is risk both of electric and acoustic shocks. These may be partly mitigated by protective devices.
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Inductive Interference with Telephone Lines. Nature 132, 925 (1933). https://doi.org/10.1038/132925c0
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DOI: https://doi.org/10.1038/132925c0