Edwin Armstrong is widely regarded as one of the foremost contributors to the field of radio-electronics and was inducted into the National Inventors Hall of Fame in 1980. Among his principal contributions were regenerative feedback circuits, the superheterodyne radio receiver, and a frequency -modulation radio broadcasting system.

As an independent inventor whose patented inventions served as important pawns in an arena of corporate conflicts over dominance in the radio industry, he devoted much money, time, and energy to efforts to establish his priority both in the legal sense and in the eyes of his peers. The frustrations that he experienced in these efforts caused his final years to unfold like a Shakespearean tragedy.

Armstrong's inventive style was somewhat unusual in that he expressed almost a phobic distrust of mathematical analysis, and his well-crafted technical papers rarely contained an equation. Instead he employed circuit diagrams, oscillograms, and graphical tube characteristics to explain his discoveries. He was like an artist except that his medium was three-dimensional combinations of vacuum tubes, resistors, inductors, and capacitors. He exhibited an intuitive grasp of the effect of changing circuit parameters and could isolate the cause of unexpected phenomena that baffled less perceptive experimenters.

Armstrong graduated with a degree in electrical engineering from Columbia University in 1913 and observed the phenomenon of regenerative feedback in vacuum-tube circuits while still an undergraduate. At Columbia, he came under the influence of the legendary professor-inventor, Michael I. Pupin, who had become wealthy from selling his loading-coil patents to the Bell Telephone Company. Pupin served as a role model for Armstrong and became an effective promoter of the young inventor. In 1915 Armstrong presented an influential paper on regenerative amplifiers and oscillators to the Institute of Radio Engineers (IRE). The paper provoked a dispute with Lee de Forest, who questioned Armstrong's interpretation and his priority in the discovery. Subsequently, regenerative feedback was incorporated into a comprehensive engineering science developed by Harold Black, Harry Nyquist, Hendrik Bode, and others in the period between 1915 and 1940. The methods of analysis and design that they developed proved highly applicable to the related field of servomechanisms during World War II. Bode characterized this convergence of control and communications as having been a "sort of shotgun marriage."

Armstrong conceived the superheterodyne receiver principle in 1918 while serving in the Army Signal Corps in France. As with regenerative feedback, there were other claimants to priority, but he played a key role in the commercialization of the invention during the early 1920's. Armstrong also acquired considerable financial gain through selling the rights to his receiver patents. The Radio Corporation of America (RCA) used his superheterodyne patent to monopolize the market for this type of receiver until 1930. The superheterodyne eventually extended its domain far beyond commercial broadcast receivers and, for example, proved ideal for microwave radar receivers developed during World War II.

In 1933, Armstrong was granted patents on a frequency-modulation system that he promoted as a superior alternative to the established amplitude-modulation broadcasting service. Wideband FM became almost a paradigm of how a generation of engineers may sometimes be so misled by a valid but limited mathematical theory as to overlook a major innovation. Armstrong drew on his own financial resources in a determined effort to establish FM broadcasting until the War intervened. His crusade for FM received additional setbacks in the post-war years from certain regulatory decisions by the Federal Communications Commission. In 1948 he brought suit against RCA for patent infringement, and the litigation process placed great stress on his resources.

The case was not resolved until after his tragic demise early in 1954. His inventive creativity had flourished in an earlier era of radio mania, but he seemed unable to adapt to the new environment of government regulation and protracted litigation after the war. In remarks given at an award ceremony in 1943, he compared patent litigation to "the serpent in the Garden of Eden."

Armstrong was highly esteemed by a generation of radio-electronics engineers and amateur radio enthusiasts. He received the first medal of honor of the IRE in 1918. The importance of his legacy might be appreciated by means of a thought experiment of imagining what the field of telecommunication would be like without regenerative feedback, the superheterodyne receiver, and FM.