Editing Edwin Howard Armstrong (section)

===Regenerative circuit===
[[File:Armstrong circuit.png|right|thumb|350px|Armstrong's "feed back" circuit drawing, from ''Radio Broadcast'' vol. 1 no. 1 1922.]]

Armstrong began working on his first major invention while still an undergraduate at Columbia. In late 1906, [[Lee de Forest]] had invented the three-element (triode) [[audion|"grid Audion"]] vacuum-tube. How vacuum tubes worked was not understood at the time. De Forest's initial Audions did not have a high vacuum and developed a blue glow at modest plate voltages; De Forest improved the vacuum for Federal Telegraph.<ref>''DeForest Radio Co. v. General Electric Co.'', [https://law.resource.org/pub/us/case/reporter/US/283/283.US.664.630.html 283 U.S. 664] (May 25, 1931). Fleming and Lilenfeld had advocated high vacuum. "Of critical importance in the present controversy is the effect of the presence of gas within the tube."  "In consequence, the low vacuum tube is more sensitive both as a detector and as an amplifier than a tube of high vacuum." "August 20, 1912, the earliest date claimed for Langmuir, was rejected rightly, we think, by the District Court, which held that Langmuir was anticipated by Arnold in November, 1912. But before the earlier date, De Forest sought and obtained a high vacuum in the audions used as amplifiers, and observed that when the vacuum was too low the blue glow effect occurred at from 15 to 20 volts. To secure higher voltages from the audions used as amplifiers and to procure the requisite high vacuum, he had some of the bulbs re-exhausted while superheated. By August 1912, the Telegraph Company used De Forest amplifying audions at 54 volts, and by November, they were used by another at 67.5 volts. This was possible only because the tubes had been exhausted of gas, which would otherwise have ionized with blue glow at from 20 to 30 volts."</ref> By 1912, vacuum tube operation was understood, and regenerative circuits using high-vacuum tubes were appreciated.

While growing up, Armstrong had experimented with the early temperamental, "gassy" Audions. Spurred by the later discoveries, he developed a keen interest in gaining a detailed scientific understanding of how vacuum tubes worked. In conjunction with Professor Morecroft he used an [[oscillograph]] to conduct comprehensive studies.<ref>[https://babel.hathitrust.org/cgi/pt?id=uva.x002212112&view=1up&seq=1175 "Operating Features of the Audion"] by E. H. Armstrong, ''Electrical World'', December 12, 1914, pages 1149-1152.</ref> His breakthrough discovery was determining that employing [[Positive feedback#In electronics|positive feedback]] (also known as [[Regenerative circuit|"regeneration"]]) produced amplification hundreds of times greater than previously attained, with the amplified signals now strong enough so that receivers could use loudspeakers instead of headphones. Further investigation revealed that when the feedback was increased beyond a certain level a vacuum-tube would go into [[Electronic oscillator|oscillation]], thus could also be used as a continuous-wave radio transmitter.

Beginning in 1913 Armstrong prepared a series of comprehensive demonstrations and papers that carefully documented his research,<ref name="Armstrong-audion">{{cite journal |doi = 10.1111/j.1749-6632.1916.tb55188.x |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hwsqz1&view=1up&seq=275 |first=E. H. |last=Armstrong |author-link=Edwin Howard Armstrong |title=Operating Features of the Audion |journal=Annals of the New York Academy of Sciences |volume=27 |issue=1 |pages=215–243 |date=August 2, 1917|s2cid = 85101768}}</ref> and in late 1913 applied for patent protection covering the regenerative circuit. On October 6, 1914, {{US patent|1,113,149}} was issued for his discovery.<ref>Lewis (1991), pages 77, 87.</ref> Although Lee de Forest initially discounted Armstrong's findings, beginning in 1915 de Forest filed a series of competing patent applications that largely copied Armstrong's claims, now stating that he had discovered regeneration first, based on a notebook entry made on August 6, 1912, while working for the Federal Telegraph company, prior to the date recognized for Armstrong of January 31, 1913. The result was an interference hearing at the patent office to determine priority. De Forest was not the only other inventor involved – the four competing claimants included Armstrong, de Forest, General Electric's [[Irving Langmuir|Langmuir]], and [[Alexander Meissner]], who was a German national, which led to his application being seized by the [[Office of Alien Property Custodian]] during World War I.<ref>''Ibid.'', page 192.</ref>

Following the end of WWI Armstrong enlisted representation by the law firm of Pennie, Davis, Martin and Edmonds. To finance his legal expenses he began issuing non-transferable licenses for use of the regenerative patents to a select group of small radio equipment firms, and by November 1920, 17 companies had been licensed.<ref>''Invention and Innovation in the Radio Industry'' by W. Rupert Maclaurin, 1949, page 122.</ref> These licensees paid 5% royalties on their sales which were restricted to only "amateurs and experimenters". Meanwhile, Armstrong explored his options for selling the commercial rights to his work. Although the obvious candidate was the [[Radio Corporation of America]] (RCA), on October 5, 1920, the [[Westinghouse Electric & Manufacturing Company]] took out an option for $335,000 for the commercial rights for both the regenerative and superheterodyne patents, with an additional $200,000 to be paid if Armstrong prevailed in the regenerative patent dispute. Westinghouse exercised this option on November 4, 1920.<ref>''Radio Manufacturers of the 1920s: Volume 3'' by Alan Douglas, 1991, page 3. Organized broadcasting barely existed when the initial amateur and experimental licenses were granted. By 1922 a broadcast boom in the US saw tremendous growth in the sale of radio receivers to the general public. Westinghouse tried to claim that these sales infringed on its rights, as they should be considered "commercial", but the courts disagreed. Thus, the companies that held these "amateur and experimental" license rights found they now had a valuable asset.</ref>

Legal proceedings related to the regeneration patent became separated into two groups of court cases. An initial court action was triggered in 1919 when Armstrong sued de Forest's company in district court, alleging infringement of patent 1,113,149. This court ruled in Armstrong's favor on May 17, 1921. A second line of court cases, the result of the patent office interference hearing, had a different outcome. The interference board had also sided with Armstrong, but he was unwilling to settle with de Forest for less than what he considered full compensation. Thus pressured, de Forest continued his legal defense, and appealed the interference board decision to the District of Columbia district court. On May 8, 1924, that court ruled that it was de Forest who should be considered regeneration's inventor. Armstrong (along with much of the engineering community) was shocked by these events, and his side appealed this decision. Although the legal proceeding twice went before the US Supreme Court, in 1928 and 1934, he was unsuccessful in overturning the decision.<ref>Douglas (1991), pages 193-198, 203.</ref>

In response to the second Supreme Court decision upholding de Forest as the inventor of regeneration, Armstrong attempted to return his 1917 [[Institute of Radio Engineers|IRE]] Medal of Honor, which had been awarded "in recognition of his work and publications dealing with the action of the oscillating and non-oscillating audion". The organization's board refused to allow him, and issued a statement that it "strongly affirms the original award".