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Who was Edwin Armstrong and what was his contribution to the radio?

Radio's premier inventor, Edwin H. Armstrong was responsible for the Regenerative Circuit (1912), the Superheterodyne Circuit (1918), the Superregenerative Circuit (1922) and the complete FM System (1933). His inventions and developments form the backbone of Radio Communications as we know it.

Edwin Armstrong patented the regenerative circuit in 1913 that fed a radio signal through an audion tube 20,000 times per second to caused stronger oscillations in the tube that generated radio waves. He made long-distance voice transmissions 1914, developed superheterodyne circuit during World War I that combined high and low frequency waves, was promoted to Major in the Signal Corps, sold patents to RCA 1920, discovered FM transmission 1933 but rejected by Sarnoff at RCA who was trying to develop television.

For more detailed information please keep reading from this article that was Originally published in Dictionary of American Biography, Supplement Five, pp. 21 - 23; Charles Scribner Sons, New York.

ARMSTRONG, EDWIN HOWARD (Dec. 18, 1890 -- Jan. 31, 1954), electrical engineer and inventor of three of the basic electronic circuits underlying all modern radio, radar, and television, was born in New York City, the first child of John and Emily Smith Armstrong, both native New Yorkers. His mother had been a teacher in the public schools and his father was vice president of the United States branch of the Oxford University Press. The family soon moved to the suburban town of Yonkers, N.Y., where they lived in a house on a bluff overlooking the Hudson River.

Armstrong decided to become an inventor when he was fourteen and began filling his bedroom with a clutter of homemade wireless gear. His imagination was fired by the Boy's Book of Inventions and by Guglielmo Marconi, who a few years before had sent the first wireless signals across the Atlantic. But wireless telegraphy was still in a primitive state. Its crude spark-gap transmitters produced electromagnetic wave signals so weak that sunlight washed them out through most daytime hours, while its iron-filing or magnetic receivers were cruder still, requiring tight earphones and quiet rooms to catch the faint Morse code signals that were all the early wireless was capable of transmitting. As a student at Yonkers High School (1905-1910), Armstrong built an antenna mast, 125 feet tall, on the family lawn to study wireless in all its aspects. He worked with every new device that came along, among them the so-called audion tube invented in 1906 by Lee deForest. But none of the instruments were able to amplify weak signals at the receiver, nor yet to provide stronger, more reliable power at the transmitter. On graduating from high school, Armstrong began to commute by motorcycle to Columbia University's school of engineering to pursue his studies further.

While a junior at Columbia, Armstrong made his first major invention. Long analysis of the action within the audion tube suggested to him that it might be used to greater effect. The tube was based upon Thomas Edison's 1883 discovery in his early lamp of a tiny anomalous electric current that flowed across a gap from the filament to a metal plate. In 1904 an English inventor, John Ambrose Fleming, had shown that this effect could be used as a wireless receiver, two years later deForest had added a vital element, a wire grid between the filament and plate. But in the usual receiver circuit the tube did no more than detect weak signals. In the summer of 1912 Armstrong devised a new regenerative circuit in which part of the current at the plate was fed back to the grid to strengthen incoming signals. Testing this concept in his turret room in Yonkers, he began getting distant stations so loudly that they could be heard without earphones. He later found that when feedback was pushed to a high level the tube produced rapid oscillations acting as a transmitter and putting out electromagnetic waves. Thus this single circuit yielded not only the first radio amplifier but also the key to the continuous-wave transmitter that is still at the heart of all radio operations.

Armstrong received his engineering degree in 1913, filed for a patent, and returned to Columbia as an instructor and as assistant to the professor and inventor, Michael Pupin. Before his new circuit could gain wide use, however, awaiting improvements in the vacuum tube, the United States was plunged into World War I and Armstrong was commissioned as an officer in the U.S. Army Signal Corps and sent to Paris. He was assigned to detect possibly inaudible shortwave enemy communications and thereby created his second major invention. Adapting a technique called heterodyning found in early wireless, but little used, he designed a complex eight-tube receiver that in tests from the Eiffel Tower amplified weak signals to a degree previously unknown. He called this the superheterodyne circuit, and although it detected no secret enemy transmissions, it is today the basic circuit used in 98 percent of all radio and television receivers.

Armstrong returned to Columbia with the rank of major and the ribbon of France's Legion of Honor. By then, wireless was ready to erupt into radio broadcasting. In 1920, on a bid from Westinghouse Electric and Manufacturing Company, he sold rights to his two major circuits for $335,000.00. Later he sold a lesser invention, the superregenerative circuit, to the newly organized Radio Corporation of America (RCA) for a large block of stock. Upon the success of early radio broadcasting, he became a millionaire, but he continued at Columbia University as a professor and eventual successor to Pupin. After a celebratory trip to Paris, he returned to court Marion MacInnes, secretary to the president of RCA, David Sarnoff. On Dec. 1, 1923 they were married.

As the 1920's wore on, Armstrong found himself enmeshed in a corporate war to control radio patents. His basic feedback patent had been issued on Oct. 6, 1914. Nearly a year later deForest filed for a patent on the same invention, which he sold with all audion rights to the American Telephone and Telegraph Company (AT & T). As radio began to boom, AT & T mounted a broad attack to overturn Armstrong's patent in favor of deForest's. The battle went through a dozen courts between 1922 and 1934. Armstrong, backed by Westinghouse and RCA, won the first round, lost a second, was stalemated in a third, and finally, in a last-ditch stand before the Supreme Court