Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American engineer and inventor who created FM (frequency modulation) radio and the superheterodyne receiver system. These inventions improved radio communication by reducing interference and increasing signal clarity.

He held 42 patents and received many awards, including the first Medal of Honor from the Institute of Radio Engineers (now IEEE), the French Legion of Honor, the 1941 Franklin Medal, and the 1942 Edison Medal. During World War I, he served as a major in the U.S. Army Signal Corps and was often called "Major Armstrong." He was inducted into the National Inventors Hall of Fame and the International Telecommunication Union’s list of great inventors. He was also added to the Wireless Hall of Fame after his death in 2001. Armstrong studied at Columbia University and taught there for most of his life.

Armstrong faced legal disputes with Lee de Forest and David Sarnoff, two other important figures in early radio development. These long court cases affected his health and finances, leading to the end of his marriage and his death by suicide in 1954. After his death, his wife, Marion, continued his legal cases and won several important court cases and settlements.

Early life

Edwin Howard Armstrong was born on December 18, 1890, in Chelsea, New York City, as the oldest of three children of John Armstrong and Emily Smith. His father worked at the American branch of the Oxford University Press, which published bibles and classical works, and later became vice president. His parents met at the North Presbyterian Church, located at 31st Street and Ninth Avenue. His mother’s family had close connections to Chelsea and helped with church activities. When the church moved north, the Smith and Armstrong families followed. In 1895, the Armstrong family moved from their brownstone row house at 347 West 29th Street to a similar house at 26 West 97th Street on the Upper West Side. The family lived comfortably as middle-class citizens.

At age eight, Armstrong contracted Sydenham’s chorea, a rare but serious nervous system condition caused by rheumatic fever. For the rest of his life, he had a physical habit that worsened when he was excited or stressed. Because of this illness, he stopped attending public school and was taught at home for two years. To improve his health, the Armstrong family moved to a house overlooking the Hudson River at 1032 Warburton Avenue in Yonkers. The Smith family later moved next door. Armstrong’s condition and time away from school made him socially isolated.

From an early age, Armstrong was interested in electrical and mechanical devices, especially trains. He enjoyed heights and built a homemade backyard antenna tower with a special chair for climbing up and down, which worried neighbors. Much of his early research was done in the attic of his family’s home.

In 1909, Armstrong enrolled at Columbia University in New York City. He joined the Epsilon Chapter of the Theta Xi engineering fraternity and studied under Professor Michael Pupin at the Hartley Laboratories, a research unit at Columbia. Another professor, John H. Morecroft, later described Armstrong as very focused on subjects he liked but less interested in other topics. Armstrong questioned common beliefs and often challenged professors and peers. For example, he once tricked a visiting professor from Cornell University who he disliked into receiving a severe electrical shock. He believed practical work was more important than theory, saying progress came from experimenting and thinking, not just math.

Armstrong graduated from Columbia in 1913 with an electrical engineering degree.

During World War I, Armstrong served in the Signal Corps as a captain and later a major.

After college, he received a one-year appointment as a laboratory assistant at Columbia for $600. Later, he worked as a research assistant under Professor Pupin for $1 a year. Unlike most engineers, Armstrong never worked for a company. Instead, he funded his own independent research and development lab at Columbia and owned his patents outright.

In 1934, Armstrong took over a position left vacant by the death of John H. Morecroft, becoming a professor of Electrical Engineering at Columbia. He held this role for the rest of his life.

Early work

Armstrong started working on his first major invention while he was still a student at Columbia University. In late 1906, Lee de Forest created the three-element (triode) "grid Audion" vacuum tube. At that time, scientists did not fully understand how vacuum tubes worked. De Forest's early Audions had poor vacuum quality and produced a blue glow at low voltages. He later improved the vacuum for Federal Telegraph. By 1912, scientists understood how vacuum tubes operated, and circuits using high-vacuum tubes became widely recognized.

As a young man, Armstrong experimented with early Audions, which were unstable and unreliable. Inspired by later discoveries, he became interested in learning how vacuum tubes functioned. With Professor Morecroft, he used an oscillograph to study them. His major discovery was that using positive feedback, also called "regeneration," could amplify signals hundreds of times stronger than before. This made it possible for receivers to use loudspeakers instead of headphones. Further research showed that increasing feedback beyond a certain level caused vacuum tubes to produce continuous waves, which could also be used as radio transmitters.

In 1913, Armstrong created detailed demonstrations and wrote papers about his research. That same year, he applied for a patent to protect his regenerative circuit. On October 6, 1914, the U.S. patent 1,113,149 was granted for his discovery. Lee de Forest at first dismissed Armstrong's findings, but in 1915, he filed competing patent applications, claiming he had discovered regeneration first. De Forest cited a notebook entry from August 6, 1912, while working for Federal Telegraph, which was earlier than Armstrong's January 31, 1913, date. This led to a legal hearing at the patent office to determine who had priority. Other inventors, including Irving Langmuir of General Electric and Alexander Meissner of Germany, were also involved. Meissner’s application was seized by the Office of Alien Property Custodian during World War I.

After World War I ended, Armstrong hired a law firm to represent him. To pay for legal costs, he gave non-transferable licenses to use his regenerative patents to small radio companies. By November 1920, 17 companies had been licensed. These companies paid 5% royalties on sales, but only to "amateurs and experimenters." Armstrong also explored selling commercial rights to his work. Although the Radio Corporation of America (RCA) seemed like a good choice, Westinghouse Electric & Manufacturing Company secured an option for $335,000 for both the regenerative and superheterodyne patents, with an additional $200,000 if Armstrong won the patent dispute. Westinghouse exercised this option in November 1920.

Legal cases about the regeneration patent split into two groups. In 1919, Armstrong sued de Forest’s company for patent infringement. A court ruled in Armstrong’s favor in 1921. A second set of cases, based on the patent office hearing, had a different outcome. The interference board supported Armstrong, but he refused to settle for less than full compensation. De Forest continued fighting and appealed the decision. In 1924, a court ruled that de Forest was the inventor of regeneration. Armstrong and many engineers were surprised by this. He appealed the decision, but the U.S. Supreme Court upheld the ruling in 1928 and 1934.

After the Supreme Court decision, Armstrong tried to return his 1917 IRE Medal of Honor, which recognized his work on vacuum tubes. The IRE board refused, stating it strongly supported the original award.

The United States entered World War I in April 1917. Later that year, Armstrong was commissioned as a captain in the U.S. Army Signal Corps and assigned to a laboratory in Paris, France, to develop radio communication for the Allied forces. He returned to the U.S. in 1919 as a major. During both world wars, Armstrong allowed the U.S. military free use of his patents.

During this time, Armstrong’s most important achievement was creating the "supersonic heterodyne" radio receiver, later called the "superheterodyne" circuit. This design made radios more sensitive and selective, and it is still widely used today. The key idea was mixing the incoming radio signal with a locally generated signal of a different frequency, creating a fixed intermediate frequency (I.F.) that was easier to amplify. In 1919, Armstrong applied for a patent for the superheterodyne circuit, which was granted the next year. He later sold this patent to Westinghouse. The patent was challenged, leading to another patent office hearing. Armstrong lost this battle, though it was less controversial than the regeneration dispute.

The challenger was Lucien Lévy of France, who had worked on Allied radio communication during World War I. Lévy had French patents from 1917 and 1918 covering similar ideas. AT&T, interested in radio development for telephone networks, bought the U.S. rights to Lévy’s patent and disputed Armstrong’s claim. Court reviews continued until 1928, when the District of Columbia Court of Appeals ruled that seven of Armstrong’s patent claims belonged to Lévy, with one each to Ernst Alexanderson of General Electric and Burton W. Kendall of Bell Laboratories.

Although early radios often used regeneration, Armstrong approached RCA’s David Sarnoff, whom he had known since 1913, about offering superheterodyne radios to the public. Cross-licensing agreements between RCA, Westinghouse, and AT&T allowed Armstrong to use Lévy’s patent freely. Early superheterodyne designs were complex and expensive, requiring multiple tuning knobs and nine vacuum tubes. With RCA engineers, Armstrong simplified the design. RCA introduced its superheterodyne Radiola sets in 1924, which were immediately successful and greatly increased the company’s profits. These sets were so valuable that RCA refused to license the superheterodyne technology to others.

Wide-band FM radio

"Static" interference – unwanted sounds from sources like thunderstorms and electrical devices – caused problems for early radio communication using amplitude modulation (AM). Many inventors tried to solve this issue but had little success. In the mid-1920s, Edwin Armstrong began researching a solution. He first tried changing how AM signals worked but did not succeed.

One idea was using frequency modulation (FM). Instead of changing the strength of the signal as AM does, FM changes the frequency of the signal to carry sound. In 1922, John Renshaw Carson of AT&T wrote a mathematical study showing that FM did not improve radio quality compared to AM. However, his analysis only covered a type of FM now called "narrow-band" FM, which limited his findings.

In 1928, Armstrong started studying FM. He learned about an RCA project testing whether FM shortwave signals were less affected by static than AM. In 1931, RCA engineers built an FM shortwave link that broadcast a fight from California to Hawaii. They noticed that FM signals seemed less disturbed by static. However, the project did not advance much further.

Working in secret in a basement lab at Columbia University, Armstrong developed "wide-band" FM. He discovered that making the carrier frequency change much more than the audio signal improved noise rejection. In 1933, he received five U.S. patents for this system. His main claim was that FM could reduce noise in receivers caused by vacuum tubes.

Armstrong had an agreement with RCA to let them review his patents first. In 1934, he showed his system to RCA president David Sarnoff, who found it too complex. Sarnoff wanted a simple fix for static instead. From May 1934 to October 1935, Armstrong tested FM from an RCA lab on the 85th floor of the Empire State Building. Signals were sent up to 80 miles (130 km) using an antenna on the building’s spire. These tests showed FM’s ability to reduce static and improve sound quality. However, RCA, focused on TV broadcasting, chose not to invest in FM and told Armstrong to remove his equipment.

Without RCA’s support, Armstrong funded his own development and partnered with smaller companies like Zenith and General Electric to promote FM. He believed FM could replace AM radio within five years, helping the struggling radio industry during the Great Depression. In 1936, he published a paper in the Proceedings of the IRE that explained FM’s advantages. A year later, Murray G. Crosby wrote a paper introducing the concept of "threshold," showing that FM works best when signals are strong enough.

In 1936, Armstrong presented his FM system to the U.S. Federal Communications Commission (FCC). He played a jazz record using AM and then FM. Engineers in the audience said FM sounded so clear it felt like the band was in the room. Armstrong predicted that ultra-high frequency bands would eventually dominate broadcasting, though this would require replacing all existing equipment and receivers.

In the late 1930s, the FCC explored ways to improve radio quality and increase the number of stations. In 1937, it introduced the "Apex band," which had AM stations with better sound quality. Armstrong argued that FM was a better option. That year, he funded the first FM station, W2XMN (later KE2XCC), in New Jersey. FCC engineers doubted FM signals could travel far, but the station was clearly heard 100 miles (160 km) away.

FCC studies found Armstrong’s FM system was better than the Apex band. In 1940, the FCC held hearings and announced an FM band starting in 1941, with 40 channels from 42 to 50 MHz. Existing Apex stations had to switch to FM or stop broadcasting.

Interest in FM grew, but World War II restrictions limited its development. After the war, the FCC focused on frequency allocations. RCA proposed moving FM to higher frequencies to avoid interference from tropospheric and Sporadic E propagation. Armstrong opposed this change but lost. In 1945, the FCC finalized its decision, assigning FM to 88–108 MHz and moving the old FM band to other uses. A period allowing stations to broadcast on both old and new bands ended.

FM radar

During World War II, Armstrong focused on studying continuous-wave FM radar using money from government contracts. He believed that the ability of wide-band FM to reduce interference and the use of a narrow receiver setting could help increase the radar's range. Most of the research happened at Armstrong's laboratory in Alpine, New Jersey. A second set of equipment was sent to the U.S. Army's Evans Signal Laboratory. However, the results were unclear, the war ended, and the Army stopped the project.

Later, the Evans team started a project called Project Diana to test sending radar signals to the moon. Calculations showed that regular pulsed radar, like the SCR-271 model, would not work. Instead, they needed higher power, longer transmitter pulses, and very narrow receiver settings. They found that Armstrong's equipment could be changed to meet these needs. The FM modulator in the transmitter was turned off, and the transmitter was adjusted to send short, continuous-wave pulses lasting a quarter of a second. The narrow-band receiver, which tracked the transmitter's frequency, had a special tuning control to handle the possible 300 Hz Doppler shift in the echoes from the moon. On January 10, 1946, they successfully sent a radar signal to the moon and received it back.

Death

Many long patent disputes hurt Armstrong's health, and his behavior became unpredictable. At one point, he believed someone had poisoned his food and demanded that his stomach be pumped. According to They Made America, written by Sir Harold Evans and others, Armstrong did not realize how his struggles affected Marion. Marion spent months in a mental hospital after she tried to jump into the East River.

The legal battles also nearly caused Armstrong to lose all his money. On November 1, 1953, Armstrong told Marion that he had used almost all his financial resources. In better times, money for their retirement was placed in her name, and he asked her to release some of those funds to continue fighting in court. She refused and suggested he accept a settlement. Angry, Armstrong grabbed a fireplace poker and hit her on the arm. Marion left the apartment to stay with her sister and never saw Armstrong again.

After about three months apart, on the night of January 31–February 1, 1954, Armstrong jumped to his death from a window in his 12-room apartment on the 13th floor of River House in Manhattan, New York City. The New York Times reported that his two-page suicide note to his wife said he was heartbroken about not seeing her again and expressed deep regret for hurting her, "the dearest thing in his life." The note ended with, "God keep you and Lord have mercy on my Soul."

David Sarnoff denied any role in Armstrong's death, telling Carl Dreher directly, "I did not kill Armstrong." After his death, a friend estimated Armstrong spent 90% of his time fighting lawsuits against RCA. U.S. Senator Joseph McCarthy (R-Wisconsin) reported that Armstrong had recently met with one of his investigators and was "mortally afraid" that secret radar discoveries by him and other scientists "were being fed to the Communists as fast as they could be developed."

After her husband's death, Marion Armstrong took control of his estate's legal cases. In late December 1954, it was announced that a settlement of "approximately $1,000,000" had been reached with RCA. Dana Raymond of Cravath, Swaine & Moore in New York represented Marion in the case. Through long court battles lasting until 1967, Marion successfully proved Armstrong was the inventor of FM radio and won lawsuits against companies that had copied his five basic FM patents.

Legacy

In the 1960s, FM radio stations in the United States began to compete with AM radio stations. This growth was supported by the invention of FM stereo by General Electric and a rule from the Federal Communications Commission (FCC) called the FM Non-Duplication Rule. This rule limited large-city radio stations that had both AM and FM licenses to broadcast the same content on both frequencies for only half of their daily broadcast time. Edwin Armstrong’s FM system was also used for communication between NASA and astronauts during the Apollo space program.

In 1983, the United States Postal Service released a postage stamp in honor of Armstrong as part of a series celebrating American inventors. Armstrong is often described as "the most productive and influential inventor in radio history." The superheterodyne process, a method Armstrong developed, is still widely used in modern radio equipment.

Eighty years after Armstrong’s invention of FM technology, it began to be replaced in some areas by more efficient digital systems. The introduction of digital television removed the FM audio channel that had been used for analog television broadcasts. HD Radio technology added digital sub-channels to FM stations, and in Europe and parts of Asia, Digital Audio Broadcasting (DAB) systems were created. These systems may eventually replace some FM stations. Despite these changes, FM broadcasting is still used worldwide and remains the primary method for transmitting audio broadcasts.

Personal life

In 1923, Armstrong climbed the WJZ (now WABC) antenna on a 20-story building in New York City. He was reported to have done a handstand while on the antenna. When asked by a witness why he performed such acts, Armstrong said, "I do it because the spirit moves me." Armstrong arranged for photographs to be taken, which he sent to David Sarnoff's secretary, Marion McInnis. Armstrong and McInnis married later that year. Before the wedding, Armstrong purchased a Hispano-Suiza motor car, which he kept until his death. He drove the car to Palm Beach, Florida, for their honeymoon. A publicity photograph was taken of him giving Marion the world's first portable superheterodyne radio as a wedding gift.

Armstrong loved playing tennis until an injury in 1940. He also drank an Old Fashioned with dinner. Politically, he was described by an associate as "a revolutionist only in technology – in politics he was one of the most conservative of men."

In 1955, Marion Armstrong founded the Armstrong Memorial Research Foundation. She worked with the foundation until her death in 1979 at the age of 81. She was survived by two nephews and a niece.

Commemorations

In 1980, Armstrong was added to the National Inventors Hall of Fame. He appeared on a U.S. postage stamp in 1983. In 2000, the Consumer Electronics Hall of Fame honored him for his work and the new ideas he brought to consumer electronics. In 2001, Armstrong was added to the Wireless Hall of Fame after he passed away. Columbia University created the Edwin Howard Armstrong Professorship in the School of Engineering and Applied Science to remember him.

Philosophy Hall, the building at Columbia University where Armstrong developed FM radio, was named a National Historic Landmark. His childhood home in Yonkers, New York, was recognized by the National Historic Landmark program and the National Register of Historic Places. However, this recognition was removed after the house was torn down.

Armstrong Hall at Columbia University was named in his honor. The hall, located at the northeast corner of Broadway and 112th Street, was once an apartment building but was changed into research space after the university bought it. Today, it is home to the Goddard Institute for Space Studies, a research center that studies the atmosphere and climate. A small store in one corner of the building is Tom's Restaurant, a long-time neighborhood favorite. This restaurant inspired a song by Susanne Vega and was used in scenes for the fictional "Monk's diner" in the "Seinfeld" television show.

Another Armstrong Hall, also named for the inventor, is located at the United States Army Communications and Electronics Life Cycle Management Command (CECOM-LCMC) Headquarters in Aberdeen Proving Ground, Maryland.

In 2005, Armstrong's regenerative feedback circuit, superheterodyne circuit, and FM circuits were added to the TECnology Hall of Fame. This honor was given to "products and innovations that have had an enduring impact on the development of audio technology."

Patents

• Frequency Modulation Multiplex System, U.S. patent 2,630,497 ;
• Radio Signaling, U.S. patent 2,602,885 ;
• Frequency-Modulated Carrier Signal Receiver, U.S. patent 2,540,643 ;
• Frequency Modulation Signaling System, U.S. patent 2,323,698 ;
• Means for Receiving Radio Signals, U.S. patent 2,318,137 ;
• Method and Means for Transmitting Frequency Modulated Signals, U.S. patent 2,315,308 ;
• Current Limiting Device, U.S. patent 2,295,323 ;
• Frequency Modulation System, U.S. patent 2,290,159 ;
• Radio Rebroadcasting System, U.S. patent 2,276,008 ;
• Means and Method for Relaying Frequency Modulated Signals, U.S. patent 2,275,486 ;
• Means and Method for Relaying Frequency Modulated Signals, U.S. patent 2,264,608 ;
• Frequency Modulation Signaling System, U.S. patent 2,215,284 ;
• Radio Transmitting System, U.S. patent 2,203,712 ;
• Radio Transmitting System, U.S. patent 2,169,212 ;
• Radio Transmitting System, U.S. patent 2,130,172 ;
• Frequency Changing System, U.S. patent 2,122,401 ;
• Radio Receiving System, U.S. patent 2,116,502 ;
• Radio Receiving System, U.S. patent 2,116,501 ;
• Multiplex Radio Signaling System, U.S. patent 2,104,012 ;
• Radio Signaling System, U.S. patent 2,104,011 ;
• Radio Transmitting System, U.S. patent 2,098,698 ;
• Phase Control System, U.S. patent 2,085,940 ;
• Radio Signaling System, U.S. patent 2,082,935 ;
• Radio Transmitting System, U.S. patent 2,063,074 ;
• Radio Signaling System, U.S. patent 2,024,138 ;
• Radio Telephone Signaling, U.S. patent 1,941,447 ;
• Radiosignaling, U.S. patent 1,941,069 ;
• Radiosignaling, U.S. patent 1,941,068 ;
• Radio Broadcasting and Receiving System, U.S. patent 1,941,067 ;
• Radio Signaling System, U.S. patent 1,941,066 ;
• Wave Signaling System, U.S. patent 1,716,573 ;
• Wave Signaling System, U.S. patent 1,675,323 ;
• Wireless Receiving System for Continuous Wave, U.S. patent 1,611,848 ;
• Wave Signaling System, U.S. patent 1,545,724 ;
• Wave Signaling System, U.S. patent 1,541,780 ;
• Wave Signaling System, U.S. patent 1,539,822 ;
• Wave Signaling System, U.S. patent 1,539,821 ;
• Wave Signaling System, U.S. patent 1,539,820 ;
• Signaling System, U.S. patent 1,424,065 ;
• Radioreceiving System Having High Selectivity, U.S. patent 1,416,061 ;
• Selectively Opposing Impedance to Received Electrical Oscillations, U.S. patent 1,415,845 ;
• Multiple Antenna for Electrical Wave Transmission, U.S. patent 1,388,441 ;
• Method of Receiving High Frequency Oscillation, U.S. patent 1,342,885 ;
• Antenna with Distributed Positive Resistance, U.S. patent 1,336,378 ;
• Electric Wave Transmission (Co-patentee with Mihajlo Pupin ), U.S. patent 1,334,165 ;
• Wireless Receiving System, U.S. patent 1,113,149 ;
• Radio detection and ranging systems, 1956, U.S. patent 2,738,502 (awarded posthumously);
• Multiplex frequency modulation transmitter, 1956, U.S. patent 2,773,125 (awarded posthumously);
• Linear detector for subcarrier frequency modulated waves, 1958, U.S. patent 2,835,803 (awarded posthumously);
• Noise reduction in phase shift modulation, 1959, U.S. patent 2,871,292 (awarded posthumously);
• Stabilized multiple frequency modulation receiver, 1959, U.S. patent 2,879,335 (awarded posthumously).