In ordinary telephone communication, the voice is converted into electrical impulses which travel over a wire, are transformed into sounds again at the receiving end. In radio-telephonyas between the shore and a ship at sea, for examplethe voice is converted into waves of radiation which travel through the air. But weaves of radiation at radio frequencies can also be guided along a cable, if the stations are fixed arid if the cable can carry a wide enough frequency band. Such an arrange ment enables the cable-carried waves to be fortified by amplifiers...
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