Submarine Cable Telegraphy: Influence of Interference

The design and operation of long submarine telegraph cables are affected to an important degree by extraneous electrical interference near the ends. The amount of interference in different cases is dependent upon a number of factors, some of which can only be determined by measurements made in the vicinity. The relation is first given between the amount of interference and the operating speed of the cable, assuming the interference to be sinusoidal. This is extended to include actual interference which is not sinusoidal. Since the computations with non-sinusoidal interference are too tedious for general field use, an experimental method is given which provides results which may be used directly in determinations of the effect upon cable operation. Examples are given of the computation of the response of the receiving instrument under the influence of a transient extraneous voltage, the frequency characteristic of the receiving equipment being known. Conversely, examples are given of the computation of the frequency characteristic from the results of an experimental determination of the response of the receiving instrument to a transient impressed voltage.