Passionate radio hobbyist, at age 17 Armstrong built his first radio. In 1909 he entered Columbia University, where he graduated in engineering in 1913. That same year he created the heterodyne circuit and the valve oscillator with a jet circuit, which improved the sensitivity of radio receivers.
In 1918 he patented the superheterodyne circuit, which had already been made previously by Lucien Levy, so he lost, as a result of a long legal dispute, the authorship of the invention.
In 1919, he returned to his homeland from France (where he had participated in the War in the telecommunications service of the US Army) and became involved in a lawsuit with Lee De Forest (another great radio pioneer) with Regarding the priority of the invention of the feedback loop: after 12 years of litigation, the priority of the invention was attributed to De Forest.
Another source of patent litigation filed by Armstrong was the frequency modulation technique. During the 1930s, the only generalized modulation technique was amplitude modulation: all the equipment of the large communication companies was in danger of becoming obsolete; for this reason, there was an initial distrust of the new alternative proposed by Armstrong. The FCC, the commission in charge of assigning a band to the newly created FM technique, chose the one currently in use (87.5 – 108 MHz), although Armstrong showed the real convenience of a different frequency distribution, with in order to resize the ‘influence.
During World War II, he participated in the development of long-range frequency modulation and continuous wave radar.
Shortly before the legal terms of his patents expired, he was forced to agree to a financial agreement with the RCA to cover the high costs. He fell into a depression and committed suicide on January 31, 1954, jumping from the 13th floor of his New York home wearing a coat and hat. In the note he left to his wife, he wrote: “May God help us and have mercy on my soul. “His widow, Marion, who before marrying him was secretary to the then president of the RCA, David Sarnoff, returned to court on the patent issue, succeeding in making her position prevail towards the end of the 1970s.