Radio Extension Links to the Telephone System

O the general public, the word radio means broadcasting, and a radio set means a radio receiver for listening thereto. The average man never has any direct contact with a radio transmitter, nor with the radio telegraph which preceded the radio telephone and so utilizes the all inclusive word "radio" for that one part of it which he sees, buys, and uses. The radio engineer is not quite in that class. There is, however, much in radio with which he is unacquainted. The radio field has become so broad and extensive that it is physically impossble for anyone to keep abreast of the whole art. Since the application of radio to telephone links is a specialized field, undoubtedly much of its history and technical developments is known only sketchily or not at all to many engineers. This paper, therefore, is planned to cover this field briefly, show its general development, and describe in principle a number of devices developed for use therein, most of which are seldom if ever used in the field of broadcasting. The radio telephone was not one of those devices that an inventor springs upon an unexpecting world. On the contrary it was expected, and was the object of search and investigation for years before a practical form appeared. Because the wire telephone followed the wire telegraph, technical men expected the radio telephone to follow the radio telegraph as soon as the latter had been practically demonstrated. Telephone men developed an interest in it as soon as it was suggested. Telephony over large bodies of water, over difficult terrain, and to moving conveyances was difficult or impossible for wire telephony, and the telephone man was intrigued by the possibility of providing his circuits without the use of conducting wires.