Economic factors in the design of single-core submarine cables for carrier telephony

The author lays down the generalisation that the less the distance between any two places of equal size and importance, the greater the amount of telephone facilities required. Multiplicity of channels will be required over short distances, and can be more easily obtained by using submarine cables than radio links. Paper-insulated lead-covered cable cannot stand greater depths of submersion than 100 fathoms, and cables insulated with g.p. or similar material must be used. Of the types used up to the present there are only two suitable for any depth: ( a) single-conductor, continuously-loaded g.p. with concentric earthed return, and ( b) single-conductor, non-loaded g.p. with concentric earthed return. Carrier can only be operated over very short distances. With non-loaded cables the rate of attenuation with frequency is gradual, and there is no inter-modulation as in the case of a loaded cable. By sacrificing half the channels the range of this type of cable can be extended by operating on a 4-wire basis (two-band telephony). The paper proceeds to discuss the determination of the most economical weight of return conductor and the correct proportion of g.p. to copper.