Edwin Howard Armstrong
|This article needs additional citations for verification. (May 2013)|
|Edwin H. Armstrong|
Developed and advanced the utility of FM technology.
December 18, 1890|
Chelsea, Manhattan, New York, New York, U.S.
|Died||January 31, 1954
New York, New York, U.S.
|Occupation||Electrical engineer, inventor|
|Known for||Inventor of FM radio|
|Spouse(s)||Marion MacInnis (1922–1954; his death)|
Edwin Howard Armstrong (December 18, 1890 – January 31, 1954) was an American electrical engineer and inventor. He has been called "the most prolific and influential inventor in radio history". He invented the regenerative circuit while he was an undergraduate and patented it in 1914, followed by the super-regenerative circuit in 1922, and the superheterodyne receiver in 1918. Armstrong was also the inventor of modern frequency modulation (FM) radio transmission.
Armstrong was born in New York City, New York, in 1890. He studied at Columbia University where he was a member of the Epsilon Chapter of the Theta Xi Fraternity. He later became a professor at Columbia University. He held 42 patents and received numerous awards, including the first Institute of Radio Engineers now IEEE Medal of Honor, the French Legion of Honor, the 1941 Franklin Medal and the 1942 Edison Medal. He is a member of the National Inventors Hall of Fame and the International Telecommunications Union's roster of great inventors.
Armstrong was born in the Chelsea district of New York City to John and Emily Armstrong. His father was the American representative of the Oxford University Press, which published Bibles and standard classical works. John Armstrong, who was also a native of New York, began working at the Oxford University Press at a young age and eventually reached the position of Vice President of the American branch. Emily Smith first met John Armstrong in the North Presbyterian Church, which was located at 31st Street and Ninth Avenue. Emily Smith had strong family ties to Chelsea, which centered around the church, in which her family took an active role.
When the church moved further North the Smith and Armstrong families followed it. In 1895 the Armstrong family moved from their brownstone row house at 347 West 29th Street to another similar house at 26 West 97th Street in the Upper West Side. At the age of eight Armstrong contracted a disease that was known as St. Vitus' Dance, which left him with a lifelong tic when excited or under stress. Because of the illness Armstrong was withdrawn from school for two years. In order to improve his health the Armstrong family moved in 1902 from the Upper West Side into a house at 1032 Warburton Avenue in Yonkers, which overlooked the Hudson river. The Smith family moved into a house next door.
Armstrong's physical tic and the years he was removed from school led him to become withdrawn. Armstrong showed an interest in electrical and mechanical devices, particularly trains, from an early age.
He loved heights and constructed a makeshift radio antenna tower in his back yard. Swinging on a bosun's chair, he would hoist himself up and down the tower to the concern of his neighbors.
In late 1917, Armstrong was invited to join the U.S. Army Signal Corps with the rank of captain and was sent to Paris to help set up a wireless communication system for the Army. He returned to the United States in the fall of 1919.
During his service in both world wars, Armstrong gave the U.S. military free use of his patents. Use of these was critical to the Allied victories.
Unlike many engineers, Armstrong was never a corporate employee. He performed research and development by himself and owned his patents outright. He did not subscribe to conventional wisdom and was quick to question the opinions of his professors and his peers.
As an undergraduate, and later as a professor at Columbia University, Armstrong worked from his parent's attic in Yonkers, New York to develop the regenerative circuit, the superheterodyne receiver, and the superregenerative circuit. He studied under Professor Mihajlo Pupin at the Hartley Laboratories, a separate research unit at Columbia University. Thirty-one years after graduating from Columbia he became Professor of Electrical Engineering, filling the vacancy left by the death of Professor J. H. Morecroft. He held the position until his death.
Armstrong contributed the most to modern electronics technology. His discoveries revolutionized electronic communications. Regeneration, or amplification via positive feedback is still in use to this day. Also, Armstrong discovered that Lee De Forest's Audion would go into oscillation when feedback was increased. Thus, the Audion could not only detect and amplify radio signals, it could transmit them as well.
While De Forest's addition of a third element to the Audion (the grid) and the subsequent move to modulated (voice) radio is not disputed, De Forest did not put his device to work. Armstrong's research and experimentation with the Audion moved radio reception beyond the crystal set and spark-gap transmitters. Radio signals could be amplified via regeneration to the point of human hearing without a headset. Armstrong later published a paper detailing how the Audion worked, something De Forest could not do. De Forest did not understand the workings of his Audion.
Armstrong's service as a signal officer in World War I led to his design of the superheterodyne circuit. The discovery and development of the technology made radio receivers, then the primary communications devices of the time, more sensitive and selective. Before heterodyning, radio signals often overrode and interfered with each other. Heterodyning also made radio receivers much easier to use, rendering obsolete the multitude of tuning controls on radio sets of the time. The superheterodyne technology is still used today. There was a dispute regarding who invented superheterodyne radio. Walter Schottky claimed that he had independently invented super heterodyne radio.
Even as the regenerative-circuit lawsuit continued, Armstrong was working on another momentous invention. Working in the basement laboratory of Columbia's Philosophy Hall, he invented wide-band frequency modulation (FM) radio. Rather than varying ("modulating") the amplitude of a radio wave to encode an audio signal, the new method varied the frequency. FM enabled the transmission and reception of a wider range of audio frequencies, as well as audio free of "static", a common problem in AM radio. (Armstrong received a patent on wide-band FM on December 26, 1933.)
In 1922, John Renshaw Carson of AT&T, inventor of Single-sideband modulation (SSB modulation), had published a paper in the Proceedings of the IRE arguing that FM did not appear to offer any particular advantage. Armstrong managed to demonstrate the advantages of FM radio despite Carson's skepticism in a now-famous paper on FM in the Proceedings of the IRE in 1936, which was reprinted in the August 1984 issue of Proceedings of the IEEE.
Today the consensus regarding FM is that narrow band FM is not so advantageous in terms of noise reduction, but wide band FM can bring great improvement in signal to noise ratio if the signal is stronger than a certain threshold. Hence Carson was not entirely wrong, and the Carson bandwidth rule for FM is still important today. Thus, both Carson and Armstrong ultimately contributed significantly to the science and technology of radio. The threshold concept was discussed by Murray G. Crosby (inventor of Crosby system for FM Stereo) who pointed out that for wide band FM to provide better signal to noise ratio, the signal should be above a certain threshold, according to his paper published in Proceedings of the IRE in 1937. Thus Crosby's work supplemented Armstrong's paper in 1936.
In 1934 Armstrong began working for RCA at the request of the president of RCA, David Sarnoff. Sarnoff and Armstrong first met at a boxing match involving Jack Dempsey in 1920. At the time Sarnoff was a young executive with an interest in new technologies, including radio broadcasting. In the early 1920s Armstrong drove off with Sarnoff's secretary, Marion MacInnes, in a French sports car. Armstrong and MacInnes were married in 1923. While Sarnoff was understandably impressed with Armstrong's FM system, he also understood that it was not compatible with his own AM empire. Sarnoff came to regard FM as a threat and refused to support it any further.
From May 1934 until October 1935, Armstrong conducted the first large scale field tests of his FM radio technology from a laboratory constructed by RCA on the 85th floor of the Empire State Building. An antenna attached to the spire of the building fired radio waves at receivers about 80 miles away. However RCA had its eye on television broadcasting, and chose not to buy the patents for the FM technology. A June 17, 1936, presentation at the Federal Communications Commission (FCC) headquarters made headlines nationwide. He played a jazz record over conventional AM radio, then switched to an FM broadcast. "[I]f the audience of 50 engineers had shut their eyes they would have believed the jazz band was in the same room. There were no extraneous sounds," noted one reporter. He added that several engineers described the invention "as one of the most important radio developments since the first earphone crystal sets were introduced."
In 1937, Armstrong financed construction of the first FM radio station, W2XMN, a 40 kilowatt broadcaster in Alpine, New Jersey. The signal (at 42.8 MHz) could be heard clearly 100 miles (160 km) away, despite the use of less power than an AM radio station.
RCA began to lobby for a change in the law or FCC regulations that would prevent FM radios from becoming dominant. By June 1945, the RCA had pushed the FCC hard on the allocation of electromagnetic frequencies for the fledgling television industry. Although they denied wrongdoing, David Sarnoff and RCA managed to get the FCC to move the FM radio spectrum from 42-50 MHz, to 88-108 MHz, while getting new low-powered community television stations allocated to a new Channel 1 in the 44-50 MHz range. In fairness to the FCC, the 42-50 MHz band was plagued by frequent tropospheric and E-layer stratospheric propagation which caused distant high powered stations to interfere with each other. The problem becomes even more severe on a cyclical basis when sunspot levels reach a maximum every 11 years and lower VHF band signals below 50 MHz can travel across the Atlantic Ocean or from coast to coast within North America on occasion. Sunspot levels were near their cyclical peak when the FCC reallocated FM in 1945. The 88-108 MHz range is a technically better location for FM broadcast because it is less susceptible to this kind of frequent interference. (Channel 1 eventually had to be deleted as well, with all TV broadcasts licensed at frequencies 54 MHz or higher, and the band is no longer widely used for emergency first responders either, those services having moved mostly to UHF.)
But the immediate economic impact of the shift, whatever its technical merit, was devastating to early FM broadcasters. This single FCC action would render all Armstrong-era FM receivers useless within a short time as stations were moved to the new band, while it also protected both RCA's AM-radio stronghold and that of the other major competing networks, CBS, ABC and Mutual. Armstrong's radio network did not survive the shift into the high frequencies and was set back by the FCC decision. This change was strongly supported by AT&T, because loss of FM relaying stations forced radio stations to buy wired links from AT&T.
Furthermore, RCA also claimed invention of FM radio and won its own patent on the technology. A patent fight between RCA and Armstrong ensued. RCA's momentous victory in the courts left Armstrong unable to claim royalties on any FM receivers, including televisions, which were sold in the United States. The undermining of the Yankee Network and his costly legal battles brought ruin to Armstrong, by then almost penniless and emotionally distraught. Eventually, after Armstrong's death, many of the lawsuits were decided or settled in his favor, greatly enriching his estate and heirs. But the decisions came too late for Armstrong himself to enjoy his legal vindication.
Armstrong married Sarnoff's secretary, Marion McInnis, in December 1922. He gave Marion the world's first portable radio as a wedding gift. Armstrong bought a Hispano-Suiza motor car before the wedding, which they drove to Palm Beach, Florida for their honeymoon. He kept the car until his death. McInnis, who was born in 1898, was survived by two nephews and a niece after her death in 1979.
Financially broken and mentally beaten after years of legal tussles with RCA and others, Armstrong lashed out at his wife one day with a fireplace poker, striking her on the arm. MacInnis left their apartment to stay with her sister, Marjorie Tuttle, in Granby, Connecticut.
On January 31, 1954 Armstrong removed the air conditioner from the window and jumped to his death from the thirteenth floor of his New York City apartment. His body was found fully clothed, with a hat, overcoat and gloves, the next morning by a River House employee on a third-floor balcony. The New York Times described the contents of his two-page suicide note to his wife: "he was heartbroken at being unable to see her once again, and expressing deep regret at having hurt her, the dearest thing in his life." The note concluded, "God keep you and Lord have mercy on my Soul." After his death, a friend of Armstrong estimated that 90 percent of his time was spent on litigation against RCA. Upon hearing the news, David Sarnoff supposedly remarked, "I did not kill Armstrong."
MacInnis was able to formally establish Armstrong as the inventor of FM following protracted court proceedings over five of his basic FM patents. Until her death in 1979 she participated in the Armstrong Memorial Research Foundation that she founded.
Armstrong invented a large part of the technology of modern radio. A modern biographer has written
Why, then, have so many people never heard of Armstrong? The answer is ironic: Armstrong was all substance and no style. He could not play public relations games and was naive enough to underestimate the power of those whose interests were threatened by his inventions. At the same time, he refused to compromise. In the end, he fell victim to the very stubbornness that made possible his spectacular technical successes.
It took decades following Armstrong's death for FM broadcasting to meet and surpass the saturation of the AM band, and longer still for FM radio to become profitable for broadcasters. Two developments made a difference in the 1960s. One was the development of true stereophonic broadcasting on FM by General Electric, which resulted in the approval of an FM stereo broadcast standard by the FCC in 1961, and the conversion of hundreds of stations to stereo within a few years.
The other was an FCC rulemaking in 1966 that required broadcasters who owned both full-time AM stations and FM properties in the same city to program each of them with separate programming during a majority of the day. This meant FM no longer just simulcast AM with better sound quality, but offered unique program choices expanding what listeners could hear. Programmers took advantage by turning their FM stations into venues for formats from country to progressive rock to jazz and classical music, all with the enhanced quality that stereo sound could bring. For example, some AM stations paused Sunday morning music programming for religious voicetracks by ministers. Sister stations on FM continued the music programming.
Within a few years a majority of households were FM equipped, by the 1980s a majority of cars sold had FM stereo radios and a majority of listening in the U.S. was devoted to FM signals according to the Arbitron rating service. The stereo sound revolution, followed by the programming revolution, accomplished what cleaner and crisper sound alone was unable to achieve, and made FM radio a permanent and important part of the communications landscape.
Armstrong was of the opinion that anyone who had actual contact with the development of radio understood that the radio art was the product of experiment and work based on physical reasoning, rather than on the mathematicians' calculations and formulae (known today as part of "mathematical physics"). His work, as important as it was in its own right, was a part of a continuum of progress in communications and electronics that since his time has brought forward color television, the personal computer, the Internet, cable and satellite radio and TV, personal mobile phones, audio, video and computing, digital stereo radio on both the medium wave and VHF-FM bands, and digital high definition television on VHF, UHF, cable and satellite. Armstrong's FM system was used for communications between NASA and the Apollo program astronauts. He is of no known relation to the well-known Apollo astronaut Neil Armstrong.
After her husband's death, Armstrong’s estate finally won the case against RCA. Dana Raymond of Cravath, Swaine & Moore in New York served as counsel in that litigation. Marion Armstrong became extraordinarily wealthy as a result of FM’s commercial success and acceptance worldwide.
In 1984 Robert Mondlock copyrighted an original screenplay about Armstrong's life titled "High Fidelity".
In 1917 Armstrong was the first recipient of the IRE's, now IEEE Medal of Honor. For his wartime work on radio the French government gave him the Legion of Honor in 1919. He was awarded the 1941 Franklin Medal. He received in 1942 the AIEEs Edison Medal "for distinguished contributions to the art of electric communication, notably the regenerative circuit, the superheterodyne, and frequency modulation". The ITU added him to its roster of great inventors of electricity in 1955. In 1980 he was inducted into the National Inventors Hall of Fame, and was on a U.S. postage stamp in 1983. The Consumer Electronics Hall of Fame inducted him in 2000, "in recognition of his contributions and pioneering spirit that have laid the foundation for consumer electronics."
Philosophy Hall, the Columbia building where Armstrong developed FM, was declared a National Historic Landmark in 2003 in recognition of that fact. Armstrong's home in Yonkers also received designation in both the NHL and the National Register of Historic Places, but both were withdrawn when the house was later demolished.
Armstrong Hall at Columbia is also named in his honor. The building, at the northeast corner of Broadway and 112th Street, was originally an apartment house but was converted to research space after Columbia bought it. It is now home to the Goddard Institute for Space Studies, a research institute jointly operated by Columbia and the National Aeronautics and Space Administration dedicated to atmospheric and climate science. A storefront in the corner of the building houses Tom's Restaurant, a longtime neighborhood fixture that was featured as the fictional diner "Monk's" for establishing shots in the television series "Seinfeld". The same restaurant also inspired Susanne Vega's song "Tom's Diner".
Also, the United States Army Communications and Electronics Life Cycle Management Command (CECOM-LCMC) Headquarters at Aberdeen Proving Ground, Maryland is named Armstrong Hall in his honor.
Armstrong received 42 patents in total; a selection are listed below:
- U.S. Patent 1,113,149 : "Wireless Receiving System"
- U.S. Patent 1,334,165 : "Electric Wave Transmission" (Note: Co-patentee with Mihajlo Pupin)
- U.S. Patent 1,336,378: "Antenna with Distributed Positive Resistance"
- U.S. Patent 1,342,885 : "Method of Receiving High Frequency Oscillation"
- U.S. Patent 1,415,845 : "Selectively Opposing Impedance to Received Electrical Oscillations" (Note: Co-patentee with M. I. Pupin)
- U.S. Patent 1,424,065: "Signaling System"
- U.S. Patent 1,611,848 : "Wireless Receiving System for Continuous Wave"
- U.S. Patent 1,941,066 : "Radio Signaling System" (Note: This is one of the patents issued for wideband FM in 1933.)
- U.S. Patent 1,941,068 : "Radiosignaling" (Note: This is one of the patents issued for wideband FM in 1933.)
- U.S. Patent 1,941,069 : "Radiosignaling" (Note: This is one of the patents issued for wideband FM in 1933.)
Many of Armstrong's inventions were ultimately claimed by others in patent lawsuits. In particular, the regenerative circuit, which Armstrong patented in 1914 as a "wireless receiving system," was subsequently patented by Lee De Forest in 1916; De Forest then sold the rights to his patent to AT&T. Between 1922 and 1934, Armstrong found himself embroiled in a patent war, between himself, RCA, and Westinghouse on one side, and De Forest and AT&T on the other. At the time, this action was the longest patent lawsuit ever litigated, at 12 years. Armstrong won the first round of the lawsuit, lost the second, and stalemated in a third. Before the Supreme Court of the United States, De Forest was granted the regeneration patent in what is today widely regarded as a misunderstanding of the technical facts by the Supreme Court justices.
By early 1923, however, Armstrong was a millionaire as a result of licensing his patents to RCA. In 1946 the FCC's decision to use Armstrong's FM system as the standard for NTSC television sound gave Armstrong another chance at royalty payments. However, RCA refused to pay him royalties and encouraged other television makers not to pay them either.
- Armstrong oscillator – basic circuit for reception of AM radio signals
- Armstrong Tower – tall lattice tower built and used by Edwin Armstrong in 1938
- Armstrong Phase Modulator
- Awards named after E. H. Armstrong
- Regenerative circuit
- Tsividis, Yannis (Spring 2002). "Edwin Armstrong: Pioneer of the Airwaves". Columbia Magazine. Living Legacies: Great Moments and Leading Figures in the History of Columbia University. New York: Columbia University. Retrieved December 12, 2010.
- Campbell, Richard; Christopher R. Martin, Bettina Fabos (2011). Media and Culture: An Introduction to Mass Communication, 8th Ed.. MacMillan. p. 124. ISBN 0312644655.
- "The Armstrong Patent". Radio Broadcast (Doubleday, Page, & Co.) 1 (1): 71–72. May 1922.
- "Armstrong, FM Inventor, Dies In Leap From East Side Suite". The New York Times. February 2, 1954. p. 1. ISSN 0362-4331. "Maj. Edwin H. Armstrong, whose inventions provided much of the basis for modern broadcasting, was found dead yesterday morning on a third-floor balcony of River House, 435 East Fifty-second Street. The 63-year-old electrical engineer had plunged from a window of his luxurious thirteenth-floor apartment, apparently late Sunday evening or during the night."
- Lessing 1956, p. 22
- Lessing 1956, p. 23
- Lessing 1956, p. 26
- Lessing 1956, p. 24
- Lessing 1956, p. 27
- Wu 2010, p. 126
- "Major Armstrong Goes to Columbia". The New York Times. August 7, 1934. p. 20. ISSN 0362-4331. "The appointment of Major Edwin Howard Armstrong as Professor of Electrical Engineering at Columbia University yesterday by Dr. Nicholas Murray Butler, president of the university."
- E. H. Armstrong (August 2, 1917). "Operating Features of the Audion". Annals of the New York Academy of Sciences 27 (1): 215–243. doi:10.1111/j.1749-6632.1916.tb55188.x.
- Raymond, Dana M. "Air War: Legal Battles Over FM Radio". Fathom. Columbia University.
- J.R. Carson, Notes on the theory of modulation, Proc. IRE, vol. 10, no. 1 (February 1922),pp. 57-64
- E.H. Armstrong, A method of reducing disturbances in radio signaling by a system of frequency modulation, Proc. IRE, vol. 24, no. 5 (May 1936),pp. 689-740.
- E.H. Armstrong, A method of reducing disturbances in radio signaling by a system of frequency modulation, Proc. IEEE, vol. 72, no. 8 (August 1984),pp. 1042-1062.
- M.G. Crosby, Frequency modulation noise characteristics, Proc. IRE, vol. 25, no. 4 (April 1937), pp. 472-514.
- Wu 2010, p. 125
- Mike Katzdorn. "Beginning of Armstrong's FM station W2XMN at Alpine, NJ (1937)". Retrieved December 19, 2011.
- United Press report, "Radio Set-up Eliminates All Noise," Ogden Standard-Examiner, June 18, 1936, p1
- "Armstrong, Edwin Howard". Current Biography (The H. W. Wilson Company): 23–26. 1940.
- "Esther Armstrong, 81, the Wife Of Inventor of FM Radio System". The New York Times. August 10, 1979. p. A13. ISSN 0362-4331. "Esther Marion Armstrong, the wife of the late Maj. Edwin Howard Armstrong, a leading American inventor, died Wednesday at the Exeter (N.H.) Hospital, after a brief illness. She was 81 years old and lived in Rye Beach, N.H."
- Ken Burns' documentary film, "Empire of the Air"
- Stashower, Daniel (2002), The Boy Genius and the Mogul: the untold story of television, New York: Broadway Books, ISBN 0767907590, "His health began to suffer and his behavior grew erratic. On one occasion he came to believe that someone had poisoned his food and insisted on having his stomach pumped. On another, his wife fled the house as Armstrong lashed out with a fireplace poker."
- Waldemar Kaempffert (December 9, 1956). "Stubborn genus". The New York Times. p. 297. Retrieved February 4, 2012. "After he penned the last sentence, "God keep you and the Lord have mercy on my soul," he put on his overcoat, hat and gloves and stepped out of a window thirteen stories above the ground."
- "Armstrong Suit Over FM Settled". The New York Times. December 31, 1954. p. 20. ISSN 0362-4331. "The Radio Corporation of America and the National Broadcasting Company have settled for "approximately $1,000,000" claims against them by the estate of the late Maj. Edwin H. Armstrong."
- John Griffith (January 1, 2001). "Edwin Howard Armstrong". Find A Grave. Retrieved December 20, 2011.
- "IEEE Medal of Honor". IEEE Global History Network. IEEE. June 27, 2011. Retrieved July 7, 2011.
- Sheire, James (July 1975). "National Register of Historic Places Inventory/Nomination: Edwin H. Armstrong House". Retrieved January 25, 2008. (includes 1 photo)
- "Withdrawal of National Historic Landmark Designation: Edwin H. Armstrong House". National Historic Landmark summary listing. National Park Service. Retrieved January 25, 2008.
- Lewis 1991
- Lessing, Lawrence (1956), Man of High Fidelity: Edwin Howard Armstrong, a biography, Philadelphia: Lippincott
- Wu, Tim (2010), The Master Switch, New York: Alfred A. Knopf, ISBN 978-0-307-26993-5
- Lewis, Tom (1991), Empire of the air: the men who made radio, New York: Edward Burlingame Books, ISBN 0-06-098119-9
- Erickson, Don V. (1973), Armstrong's fight for FM broadcasting: one man vs big business and bureaucracy, University of Alabama Press, ISBN 0-8173-4818-2
- Ira Brodsky. The History of Wireless: How Creative Minds Produced Technology for the Masses. St. Louis: Telescope Books, 2008.
- Ken Burns. Empire of the Air. Documentary that first aired on PBS in 1992.
- Gary L. Frost. Early FM Radio: Incremental Technology in Twentieth-Century America. Baltimore: Johns Hopkins University Press, 2010. ISBN 0-8018-9440-9, ISBN 978-0-8018-9440-4.
- Süsskind, Charles (1970). "Armstrong, Edwin Howard". Dictionary of Scientific Biography. New York. pp. 287–288 Charles Scribner's Sons. ISBN 0-684-10114-9.
|Wikimedia Commons has media related to Edwin Howard Armstrong.|
|Wikiquote has a collection of quotations related to: Edwin Howard Armstrong|
- Armstrong Memorial Research Foundation - The Armstrong Foundation disseminates knowledge of Armstrong's research and achievements
- Houck Collection - A collection of images and documents that belonged to Armstrong's assistant, Harry W. Houck, which have been annotated by Mike Katzdorn.
- Rare Book & Manuscript Library Collections - A collection of images and documents at Columbia University
- The Broadcast Archive - A brief biography by Donna Halper
- Ammon, Richard T., "The Rolls Royce Of Reception : Super Heterodynes - 1918 to 1930".
- IEEE History Center's Edwin H. Armstrong : Excerpt from "The Legacy of Edwin Howard Armstrong," by J. E. Brittain Proceedings of the IEEE, vol. 79, no. 2, February 1991
- Hong, Sungook, "A History of the Regeneration Circuit: From Invention to Patent Litigation" University, Seoul, Korea (PDF)
- Who Invented the Superhetrodyne? The history of the invention of the superhetrodyne receiver and related patent disputes
- Yannis Tsividis, "Edwin Armstrong: Pioneer of the Airwaves", 2002. A profile on the web site of Columbia University, Armstrong's alma mater