The Invention of the Radio
Radio is a wireless means of communication. Radio is widely used as an information medium and for entertainment. Almost all areas of the United States and Canada have one or more commercial radio stations, many of which broadcast 24 hours a day. Radio stations vary widely in programming. Some broadcast nothing but popular music and short news announcements, while others may schedule discussion programs, sports events, or classical music. Almost all homes in the United States and Canada have one or more radio receivers, and many automobiles are equipped with radios.
In addition to its wide use as an entertainment medium, radio is used for communication where it is expensive or impossible to lay telephone or telegraph cables between two points. Thus, radio is used to communicate between airplanes and airports, ships and ports, police cars and headquarters, and explorers and civilization.
The Development of the Radio
Radio, as with so many developments that have profoundly affected the lives of civilized peoples, began in laboratory experiments remote from the thought of practical applications. Unexplained observations gradually accumulated from 1780 to 1888; work was done on electromagnetic waves by Clerk Maxwell and later by Heinrich Hertz. Guglielmo Marconi (1874-1937) knew of Hertz's laboratory successes from his tutor, Professor Righi, and began his own experiments in 1895. He had obtained contracts for supplying short-distance shipping information to Lloyds and results of the Kingstown Regatta to a Dublin newspaper in 1898. In December 1901 he announced to an incredulous world that he had received signals in Newfoundland from Poldhu in Cornwall. By 1907 he was operating on a limited scale a public transatlantic radio telegraph system.
Early radio transmitters depended on the crude, but controllable, effects following the passage of a powerful spark between electrodes. There were no amplifiers. Sir John Ambrose Fleming, in 1904, produced a thermionic valve which was a very sensitive and stable detector, but was incapable of amplification. The American, Lee de Forest, in 1907, added a third electrode or 'grid' to such a valve, thus obtaining an instrument capable of amplification, but he did not publish his researches until 1913, by which year Meissner, in Germany, had actually used the Lieben-Reiss relay of 1911 as a generator of oscillations and an amplifier. The importance of these developments would be hard to overestimate, since one of the most crippling features in early radio developments was the difficulty of getting reliable signals at long range; the currents received at any distance were so minute without amplification that they could hardly be detected. The First World War stimulated the development of valve (or tube) amplifiers, war requiring rapid communication. The telegraph and telephone had been hailed as great advances in this respect, but the ability to communicate without intervening wires was doubly welcome. Developments in the war period were great, but signalling was almost exclusively in code.
The transmission of speech and music by radio dates back to 1906, when R. A. Fessenden (who claimed to have heard speech, even if poorly articulated, by radio in 1900) used a high-frequency alternator as a power source at Brant Rock, U.S.A. The cost was high, and the quality range very poor, so that regular broadcasting was not at the time in contemplation. The war of 1914-1918, though it advanced radio in other respects, was doubtless responsible for delaying anything so frivolous as transmissions of music. It was in 1921 that a station at Pittsburgh, U.S.A. and another at Writtle, England, began regular transmissions. The power of the Writtle station was only one quarter of a kilowatt, and when the British Broadcasting Corporation was incorporated in December 1922 a chain of eight stations with 1^ kilowatts capacity was erected within a year. There were also eleven relay stations, each of 120 watts - a power that may be compared with that of a domestic 100-watt electric lamp. By 1924 the Daventry station of the B.B.C. was of 25 kilowatts capacity.
The quest for more and more power in broadcasting was by no means an unmixed blessing. The 500-kilowatt station could swamp all its neighbours and blanket reception from afar over a wide area. Dictatorships were quick to seize on these qualities which they hoped to turn to their own advantage. The inevitable outcome was a power race, of which the effects, particularly in Europe, are still to be found in poor quality reception.
The Second World War was as prolific as the First in advances in the art of communication by radio. Outstanding were the developments by Watson-Watt and his colleagues, who began by researches into the reflection of radio waves from the ionized layers of the upper atmosphere discovered by Kennelly and Heaviside in 1902 and at a higher level by Appleton in 1925. It is the multiple reflections from these ionized layers and from the earth's surface that make it possible for short-wave signals to be heard after passing completely round the earth, whereas it had originally been thought that they would leave the earth altogether at the visual distance from the aerial to the horizon. Watson-Watt argued that if such waves could be reflected from an ionized layer they might equally be reflected by a conducting surface such as the wings and fuselage of an aeroplane. Confirmation of this theory was obtained in 1935, but the detection and accurate registration of these minute reflections posed mechanical and electrical problems of what at one time seemed almost insuperable complexity; but in war the support was forthcoming for the prosecution of researches, however costly; and from these came radar, valuable in war and a boon in peace-time navigation.
Another war-time advance was the discovery of the peculiar properties of the rare substance germanium as an amplifier and rectifier. Amplifiers of great efficiency, long life and very small size are made possible by the germanium valve. Radio, in this case, comes to the aid of telephony, since such amplifiers will be sunk at intervals as part of the first transatlantic cable telephone.