Radio broadcast .. (1922-30)

John Bull's World-Wide Radio Interesting Facts from the Technical Report of the Imperial Wireless Telegraphy Commission By J. CONRAD FLEMMING IF JOHN BULL did not have a world-wide radio scheme on his mind, he would not rank among the leading nations of the world. Uncle Sam has his own extensive radio system pretty well under way, with the partial completion of the Radio Central at Rocky Point, Long Island, while France is rushing the work on the huge Sainte Assise station, which will be the largest in existence. Germany has, or rather had, an ambitious world-wide radio system, with the powerful Nauen and Eilvese stations as the starting point. But we are primarily interested in John Bull's world-wide radio scheme in this case, because of a report of the Wireless Telegraphy Commission which, in accordance with the suggestion of the Imperial Wireless Telegraphy Committee, was appointed in 1920 to make recommendations regarding the sites and apparatus for the stations of the Imperial Wireless Chain. The Commission comprises such eminent men as Lord Milner, Dr. W. H. Eccles, the well-known authority on radio communication, L. B. Turner, E. H. Shaughnessy, and Lt. Col. C. G. Crawley. So the report, as might well be expected, is replete with interesting facts concerning long-distance radio communication, incorporating, as it does, the best existing practice as well as the revelations of the radio laboratory. The report starts out by pointing to the fact that the Imperial Wireless Telegraphy Committee recommended that the vacuum tube transmitters should be capable of delivering at least 120 kilowatts to the aerial and that double this power may be within the range of possibility in the near future. Mention is made of the excellent results obtained with large silica vacuum tube?. To-day, four or five 2^-kilowatt vacuum tubes of the silica type are being produced every week for the British Admiralty. It is estimated that twentyfour large tubes would be required to deliver 120 kilowatts to the aerial. If a vacuum tube transmitter were operated 24 hours per day, without rest, it would require between 36 and 1 08 tubes per year for renewals. If glass tubes were employed instead of silica, then about four times as many would be required for equipment and for renewals. So for the present the problem is to key up the vacuum tube industry in order to turn out the requisite number of tubes. The Report goes into a discussion of costs for vacuum tubes and replacements. It is claimed that the filaments of burnt-out tubes can be 'renewed, thus reducing replacement costs materially. It is hoped to realize a filament life of 2,000 to even 6,000 hours, eventually. That vacuum tubes are not altogether an experiment in long-distance communication is evident from the report's mention of the Marconi Company's experiments with this type of transmitter. Commercial traffic has been established across the Atlantic by means of vacuum tubes, so we are told, using less than 30-kilowatt input at Clifden, Ireland. The German Telefunken Company has also had good results with vacuum tubes. The Commission visited the Carnavon station and witnessed the trials with the largest vacuum tube set yet constructed. Forty-eight glass vacuum tubes were assembled, with an input of about loo kilowatts. By overloading the tubes it was possible to employ an input of 1 50 kilowatts. The signals were intercepted in India and Australia. The matter of wavelengths is an important one. Extensive experiments have been conducted by the Wireless Telegraphy Commission between the Admiralty station at Horsea and Egypt. The conclusion is that the best signals are those obtained at night by the use of relatively short waves, while the best day signals are those using long waves. Then there is the question of transmitting aerials and masts and towers. In connection with vacuum tube transmitters, it is held that the high aerial with relatively small area is preferable to the low aerial with a large area.