Modern systems of multi-channel telephony on cables

Following a brief reference to progress in the application of carrier telephony to circuits in cables in this and other countries, an account is given of the carrier system operating between Bristol and Plymouth. This system affords 12 telephone channels per pair in the range 12 to 60 kc. Separate cables are provided for the two directions of transmission, and negative-feedback repeaters are provided at intervals of approximately 20 miles. When fully equipped the system will provide 228 circuits. The account of this system is followed by a description of the 4-tube underground coaxial cable which has been installed between London and Birmingham and of the modulating and repeater equipment that has been developed to operate 320 carrier telephone channels in the range 0.5¿2.1 Mc. Repeaters are provided at intervals of approximately 7 miles, separate tubes being used for the two directions of transmission. Applications to television and the probable line of development of multi-channel and wide-band systems are discussed.