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Alternator-Transmitter Development (1891-1922)
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Radio signals were originally produced by spark transmitters, which were noisy and inefficient. So experimenters worked to develop "continuous-wave" -- also known as "undamped" -- transmitters, whose signals went out on a single frequency, and which could also transmit full-audio signals. High-speed electrical alternators was one approach used to generate continuous-wave signals, and by 1919 international control of the Alexanderson alternator-transmitter was considered so important that it triggered the formation of the Radio Corporation of America. However, within just a few years alternator-transmitters would become obsolete.
Early Development -- Reginald Fessenden -- George Squier -- Later Development


All early radio work used spark transmitters, which could only transmit the dots-and-dashes of Morse code. But, just as the telegraph had led to the telephone, various experimenters worked to develop radio transmitters which could transmit full audio, although it would take a number of years before cost efficient systems would be developed. In a 1891 lecture, Frederick T. Trouton noted that if an electrical alternator could somehow be run fast enough, it would generate electromagnetic radiation, as reported in
Radiation of Electric Energy--Alternator extract, from the January 22, 1892 The Electrician (London).


However, the main proponent for using high-speed alternators as radio transmitters would be Reginald Fessenden. As early as 1891, Fessenden had investigated transmitting lower-frequency signals along telegraph lines to create a multiplex telegraph system, according to his letter,
Sine Form Curves of Alternating E. M. F., printed in the September 15, 1894 The Electrical World. In 1901, Fessenden, now doing experimental work for the U.S. Agriculture Department, applied for a U.S. patent for a radio transmitter that used a high-speed electrical alternator to produce what became known as "continuous waves". This revolutionary design was the first to employ the same basic principles which AM (mediumwave) radio stations still use today. At this time Fessenden was also busy developing a rotary-spark transmitter for the ill-fated transatlantic service, so it wasn't until late 1906 that the alternator-transmitter was perfected to the point it was ready for public demonstration. Although the transmitter was designed mainly for point-to-point telephone service, AT&T's review of this historic presentation at Brant Rock, Massachusetts, Experiments and Results in Wireless Telephony, by John Grant, The American Telephone Journal, January 26 and February 2, 1907, noted that Fessenden's invention was "admirably adapted to the transmission of news, music, etc." One day in November, 1906, while conducting audio transmission tests at Brant Rock using the new alternator-transmitter, Fessenden received a remarkable letter -- one of his operators at Macrihanish, Scotland, who wasn't even aware of the tests, reported hearing a few sentences spoken by one of Fessenden's assistants. The incident wasn't publicized at the time, and planned follow-up tests were aborted by the collapse of the Macrihanish tower. But 12 years later, Fessenden wrote a letter, The First Transatlantic Telephone Transmission, printed in the September 7, 1918 Scientific American, which detailed what he remembered about the events, while asking if any readers had additional information.


Although radio's unique ability to travel through the air without using any connecting wires immediately caught the public imagination, in many ways radio transmissions were very inefficient, because the signals tended to spread out in all directions. In 1911, George D. Squier of the U.S. Army Signal Corps successfully employed one of the new alternator-transmitters to direct low-power audio radio signals to specific locations, by using wires as wave-guides, as reviewed in
Multiplex Telephony and Telegraphy by Means of Electric Waves Guided by Wires, from the May, 1911 Proceedings of the American Institute of American Engineers and René Bache's Many Talk on One Wire, from the March, 1911 Technical World Magazine. And although Squier's main objective was to show how radio signals could be used to transmit multiple telephone conversations simultaneously along a single wire, this "guided signals" concept would be expanded over the decades into areas as diverse as carrier-current radio stations, cable television, and fiber optics.


In the October, 1916 issue of The Electrical Experimenter,
New System of Radio Telephone reviewed Edward G. Gage's work with the National Electric Signaling Company to develop a radiotelephone system at Hoboken, New Jersey, for use with the railroad. Meanwhile, Ernst Alexanderson, the lead General Electric engineer for the original Fessenden alternator, continued to work on improvements, and eventually developed high-power alternator-transmitters, as The Electrical Experimenter for August, 1916 announced A 100 K.W. Radio Frequency Alternator that had been designed by Alexanderson. During the World War One, Alexanderson constructed a 200-kilowatt station for the U.S. Navy, NFF in New Brunswick, New Jersey, which provided reliable trans-Atlantic radiotelegraph service. In Predicts 12,000 Mile Radio Phone, from the February 10, 1919 New York Sun, Lee DeForest exuberantly reviewed its potential, while an extract from Transoceanic Radio Communication, written by Alexanderson, from the October, 1920 issue of General Electric Review, covered the station's technical information. At the time this paper was published, it appeared that alternator-transmitters would be one of the most important radio technologies for the foreseeable future, and in fact the formation of Radio Corporation of America was largely the result of the fear by the U.S. government that control of alternator-transmitter technology was about to fall into Marconi -- hence British -- hands, as reviewed by the The Navy and the Radio Corporation of America chapter of Linwood S. Howeth's 1963 History of Communications-Electronics in the United States Navy.

RCA began construction of a massive complex, called Radio Central, on Long Island, New York, with plans to install ten 200-kilowatt Alexanderson alternators, to provide international communication on a near worldwide scale, as covered in 1922 by The World's Greatest Radio Station from "The Book of Radio" by Charles William Taussig. As comparatively slow mechanical devices, alternator-transmitters could only generate longwave signals. However, about the time this book was published the tremendous range of low-powered shortwave signals -- which could only be produced by vacuum-tube transmitters -- became known, making the key devices around which RCA had been formed obsolete. Only the initial two Alexanderson alternators were ever installed at Radio Central, with the plans for the additional eight canceled. Although some of the handful of alternator-transmitters already in place would continue in operation through the 1940s, construction of additional units came to an abrupt halt, with most radio international communication handled by far less costly vacuum-tube shortwave transmitters.

"After Steinmetz designed a 10,000-cycle alternator, which Fessenden found adequate but not rapid enough, the fulfillment of Fessenden's order was assigned to a newly arrived Swedish engineer, Ernst F. W. Alexanderson. Years later, Alexanderson recalled how he obtained the assignment: 'The alternator was one of the inventions I had to make in order to hold my job! The request came in from Fessenden for a high frequency alternator. That was passed along to the regular designers. They thought it was a rather fantastic thing, and I was crazy enough to undertake it.'"-- Susan Douglas, Inventing American Broadcasting, 1987.