Abstract
IN ordinary telephony the sound waves falling on the microphone vary the pressure on the carbon granules through which a current is flowing. The resistance of the circuit thus varies, and so the current varies with the sound wave and in the receiver produces sound waves exactly similar to the original waves. In radio-telephony, in place of the current in the connecting wires, we have a high-frequency current emitted from the transmitter. This is varied (modulated) by the sound waves. These modulated waves falling on a suitable receiver reproduce waves similar to the original sound waves. Better results are obtained by using conducting wires, and in particular submarine cables. The cost of the cable in this case makes it necessary that it should carry pairs of wires providing several channels of communication. The disadvantage of this type of cable is the great difficulty of laying and maintaining it in deep water. For deep sea work a single core cable is used provided with a copper sheath under the armouring to carry the return current. In 1920 the serious single-channel limitation of this type of cable was overcome by the use of carrier wave high frequencies. This enabled telephone cables to be laid and operated between Key West (Florida) and Havana, a distance of 103 nautical miles. In a paper read to the Institution of Electrical Engineers on February 23, Dr. E. W. Smith discusses the electrical requirements for this type of transmission. He also summarises the most recent advances in materials and methods of con struction and indicates probable future developments.
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Submarine Telephone Cables at Carrier Frequencies. Nature 131, 431 (1933). https://doi.org/10.1038/131431c0
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DOI: https://doi.org/10.1038/131431c0