New Broadcasting System

Editor’s Note

An engineer in the United States, Nature reports here, has developed a new kind of radio broadcasting system. Radio systems at that time worked by amplitude modulation, which encodes the signal, such as voice, in modulations of the amplitude of the carrier wave. In contrast, the new system developed by Edwin Armstrong encodes information in modulations of the frequency of the carrier wave. That gave a sharp reduction in radio interference, although there was a considerable increase in the receiver’s complexity. Although the basic principles of this scheme of frequency modulation, or FM radio, had long been known, Armstrong brought it to fruition with valves and circuits. The first transmitting station, in Alpine New Jersey, began operating soon after.　　中文

ACCORDING to a recent report by the New York Correspondent of The Times, a new type of wireless transmission and reception will be used in an experimental station now being erected at Columbia University by Major E. H. Armstrong, professor of electrical engineering in the University, and inventor of the now well-known supersonic-heterodyne receiver. The station will use the frequency-modulation system of transmission, as distinct from the amplitude-modulation system at present used by all broadcasting stations. In the former method, the frequency of the emitted carrier wave is varied by the speech and music modulation; whereas in the methods so far employed, the frequency of the carrier wave remains constant and its amplitude is varied by the applied audio-frequencies. The principles of frequency-modulation have been known since the earliest days of radio-telephony, but it has remained for Prof. Armstrong to demonstrate how these may be brought into practical use with modern valves and circuit arrangements. Among the advantages claimed for the new system are that it effects a considerable reduction of interference in radio reception, and that a much larger number of broadcasting channels will become available in any given wave-length band. Against these, however, is the serious disadvantage that special receivers are necessary for frequency-modulated transmissions, and this factor is likely to involve serious delay in the introduction of the new system into modern broadcasting technique. The first transmitting station on the new system will be at Alpine, New Jersey, opposite New York City, and it has a licence to broadcast on a frequency of 40 megacycles per second (wave-length 7.5 metres). It is also understood that suitable receivers are already being manufactured, so that the result of this practical experiment will be awaited with interest.　　中文

(143, 152; 1939)