Armstrong Demonstrates FM Radio Broadcasting Summary

  • Last updated on November 10, 2022

During the early 1930’s, Edwin H. Armstrong invented frequency-modulated radio broadcasting, although he would neither receive credit for it nor see its widespread use in his lifetime.

Summary of Event

Because the original radio broadcasts used amplitude modulation (AM) to transmit their sounds, they were subject to a sizable amount of interference and static. AM radio As amplitude modulation relies on the amount of energy transmitted, energy sources in the atmosphere between the station and the receiver can distort or weaken the original signal. This is particularly irritating when the sound being transmitted is music. Edwin H. Armstrong provided a solution to this technological constraint. A graduate of Columbia University, Armstrong made a significant contribution to the development of radio with his basic inventions for circuits for amplitude-modulated receivers. (Indeed, the money Armstrong made from his earlier inventions financed the development of the frequency modulation, or FM, system.) Armstrong was one among many contributors to AM radio. For FM broadcasting, however, Armstrong must be ranked as the most important inventor. [kw]Armstrong Demonstrates FM Radio Broadcasting (Nov. 5, 1935) [kw]FM Radio Broadcasting, Armstrong Demonstrates (Nov. 5, 1935) [kw]Radio Broadcasting, Armstrong Demonstrates FM (Nov. 5, 1935) [kw]Broadcasting, Armstrong Demonstrates FM Radio (Nov. 5, 1935) Radio;broadcasting development FM radio [g]United States;Nov. 5, 1935: Armstrong Demonstrates FM Radio Broadcasting[09040] [c]Science and technology;Nov. 5, 1935: Armstrong Demonstrates FM Radio Broadcasting[09040] [c]Inventions;Nov. 5, 1935: Armstrong Demonstrates FM Radio Broadcasting[09040] [c]Radio and television;Nov. 5, 1935: Armstrong Demonstrates FM Radio Broadcasting[09040] [c]Communications and media;Nov. 5, 1935: Armstrong Demonstrates FM Radio Broadcasting[09040] Armstrong, Edwin H. Sarnoff, David

During the 1920’s, Armstrong established his own research laboratory in Alpine, New Jersey, across the Hudson River from New York City. With a small staff of dedicated assistants, he carried out research on radio circuitry and systems for nearly three decades. At that time, Armstrong also began to teach electrical engineering at Columbia University.

From 1928 to 1933, Armstrong worked diligently at his private laboratory at Columbia University to construct a working model of a frequency-modulated radio broadcasting system. With the primitive limitations then imposed by the state of vacuum tube technology, a number of Armstrong’s experimental circuits required as many as one hundred tubes. Between July, 1930, and January, 1933, Armstrong filed four basic FM patent applications; all were granted simultaneously on December 26, 1933.

Armstrong sought to perfect FM radio broadcasting, not to offer radio listeners better musical reception but to create an entirely new radio broadcasting system. On November 5, 1935, Armstrong made his first public demonstration of FM radio broadcasting in New York City to an audience of radio engineers. An amateur station owned by Armstrong’s friend, Randolph Runyon, based in suburban Yonkers, New York, transmitted these first signals. The scientific world began to consider the advantages and disadvantages of frequency-modulated radio broadcasting. Other laboratories began to craft their own versions of FM radio broadcasting. At the then-dominant Radio Corporation of America Radio Corporation of America;FM radio (RCA), scientists began to experiment with FM radio broadcasting.

Because Armstrong had no desire to become a manufacturer or broadcaster, he approached David Sarnoff, head of RCA. As owner of the top manufacturer of radio sets and the top radio broadcasting network, Sarnoff was interested in all advances of radio technology. Armstrong first demonstrated FM radio broadcasting for Sarnoff in December, 1933. This was followed by visits from RCA engineers, who were sufficiently impressed to recommend to Sarnoff that the company conduct field tests of the Armstrong system.

Edwin H. Armstrong.

(Smithsonian Institution)

In 1934, Armstrong, with the cooperation of RCA, set up a test transmitter at the top of the Empire State Building, sharing facilities with the then experimental RCA television transmitter. From 1934 through 1935, tests were conducted using the Empire State Building facility, to mixed reactions of RCA’s best engineers. AM radio broadcasting already had a performance record of nearly two decades. The engineers wondered if this new technology could replace something that had worked so well. This less than enthusiastic evaluation fueled the skepticism of RCA lawyers and salespeople. RCA had too much invested in the AM system, both as the leading manufacturer and as the dominant owner of the major radio network of the time, the National Broadcasting Company (NBC). Sarnoff was in no rush to adopt frequency modulation. Changing systems would endanger the millions of dollars RCA was making as the United States emerged from the Great Depression, and Sarnoff believed the risk was too great.

In 1935, Sarnoff advised Armstrong that RCA would cease any further research and development activity in FM radio broadcasting. (Still, engineers at RCA laboratories continued to work on frequency modulation to protect the corporate patent position.) Sarnoff declared to the press that his company would push the frontiers of broadcasting by concentrating on research and development of radio with pictures—that is, television. As a tangible sign, Sarnoff ordered that Armstrong’s FM radio broadcasting tower be removed from the top of the Empire State Building. Armstrong was outraged. By the mid-1930’s, the development of FM radio broadcasting had grown into a mission for Armstrong. For the remainder of his life, Armstrong devoted his considerable talents to the promotion of FM radio broadcasting. Armstrong was certain that Sarnoff was simply trying to suppress FM radio broadcasting to preserve RCA’s profits.

After the break with Sarnoff, Armstrong proceeded with plans to develop his own FM operation. Allied with two of RCA’s biggest manufacturing competitors—Zenith and General Electric—Armstrong pressed ahead. In June of 1936, at a Federal Communications Commission Federal Communications Commission (FCC) hearing, Armstrong proclaimed that FM broadcasting was the only static-free, noise-free, and uniform system—both day and night—available. He argued, correctly, that AM radio broadcasting had none of these qualities.

An FM radio broadcasting transmission tower was built in Alpine, New Jersey, and in 1938, station W2XMN became the first FM station. Armstrong gained backing from the regional radio network and, in cooperation, a transmitter tower was built atop Mount Asnebumskit in Massachusetts. The radio network would invest a quarter of a million dollars in FM radio stations. The central question turned from the technological to the legal: What part of the spectrum should be allocated for frequency modulation? Space on the very high frequency band was set aside, and, in the days before World War II, preliminary licenses were granted for more than fifty stations. In 1941, the FCC decreed that sound for the new television system it had approved should be telecast by FM principles. (It remains so to the present.)

In December, 1941, the United States became involved in World War II. Innovation of frequency modulation was halted, and the infant industry was maintained at an arrested stage of development. Armstrong gave the military permission to use frequency modulation with no compensation, and his patriotic gesture cost him millions when the military soon became all FM. This did, however, expand interest in FM radio broadcasting. World War II had provided a field test of equipment and use.

Armstrong’s final battle to institute FM radio broadcasting began in 1948 when he filed a lawsuit charging infringement of patents by RCA. This was a struggle for the claim of invention rather than the possible development of an industry. Armstrong would not live to see his invention of FM radio broadcasting come to mainstream use; on January 31, 1954, he committed suicide. The case was settled shortly thereafter. The court sidestepped the basic question of who had invented FM radio broadcasting but ordered RCA to pay the Armstrong estate $1 million for infringement of patents.


It would be three decades before Armstrong’s legacy of FM broadcasting had its full impact. When the FCC granted FM radio broadcasting licenses after World War II, most went to successful AM stations. The AM radio stations acquired the FM licenses to ensure that no serious competitors would threaten their market shares.

During the 1950’s, a handful of independent FM stations labored at the margins of the radio industry, playing ethnic, classical, jazz, and folk musical programming to small audiences. At that time, a radio receiver that could pick up FM radio broadcasts cost much more than a radio that could pick up the far more popular AM radio broadcasting signals. A particular impediment came with the lack of radios in automobiles that could pick up FM signals. As late as 1966, only one car radio in twenty-five was equipped to receive FM radio broadcasting.

The FCC initiated a change in 1966. To encourage greater diversity in programming, the FCC dictated that FM broadcasting licensees needed to provide at least 50 percent original programming on FM stations. That meant that those who owned an AM and FM station in the same market could no longer simulcast their signals. That is, they could no longer transmit the same signal on both outlets simultaneously. Although this meant hiring more staff and thus less profits in the short run, the disgruntled owners complied rather than lose their FM licenses. At first, there was abuse of the regulation. For example, a number of station owners simply ordered that staff members replay earlier tapes of the AM programming on the FM station. The signals were the same, but not simultaneous. Gradually, risk-taking station owners sought to differentiate their products to see if they could see greater profits in the long run. The first change came with alternative rock; then came all-jazz, all-talk, and all-sports FM stations. Listeners loved the fact that radio sounded as good as their stereo record players.

The result in the 1970’s was tremendous growth in FM radio broadcasting. By 1972, one in three radio listeners tuned in an FM station at some time during the day. Advertisers began to use FM radio stations to reach the young and affluent audiences that were turning to FM stations in greater numbers. The advertisers were attracted also by the low rates. Gross revenues soared from about $10 million for 1962 to nearly $85 million a decade later.

By the late 1970’s, FM stations were surging past AM radio broadcasts. In 1976, the average FM station began to show a profit. By 1980, nearly half of radio listeners tuned in to FM stations on a regular basis. A decade later, FM radio listening accounted for more than two-thirds of audience time, and regulators and station owners were seeking ways to boost the fortunes of AM radio broadcasting, but FM radio listening dominance persisted into the twenty-first century. Armstrong’s predictions that listeners would prefer the clear, static-free sounds offered by FM radio broadcasting had been proven correct by the mid-1980’s, nearly fifty years after Armstrong commenced his struggle to make FM broadcasting a part of commercial radio. Radio;broadcasting development FM radio

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Barnouw, Erik. A History of Broadcasting in the United States. 3 vols. New York: Oxford University Press, 1966-1970. The standard history of broadcasting in the United States. The development of FM radio broadcasting is covered in the first two of the three volumes.
  • citation-type="booksimple"

    xlink:type="simple">Bilby, Kenneth. The General: David Sarnoff and the Rise of the Communications Industry. New York: Harper & Row, 1986. Presents a detailed history of the activities of RCA and its founder, Sarnoff, in the invention and innovation of FM radio.
  • citation-type="booksimple"

    xlink:type="simple">Erickson, Don V. Armstrong’s Fight for FM Broadcasting: One Man Versus Big Business and Bureaucracy. Tuscaloosa: University of Alabama Press, 1973. Attempts to reclaim Armstrong’s role in the history of broadcasting by exposing the collaboration between the FCC and the entrenched broadcasting lobby to protect then-dominant AM radio.
  • citation-type="booksimple"

    xlink:type="simple">Head, Sydney W., Thomas Spann, and Michael A. McGregor. Broadcasting in America: A Survey of Electronic Media. 9th ed. Boston: Houghton Mifflin, 2000. The standard introduction to radio and television in the United States. Includes an analysis of the invention of FM radio broadcasting and Armstrong’s role.
  • citation-type="booksimple"

    xlink:type="simple">Inglis, Andrew F. Behind the Tube: A History of Broadcasting Technology and Business. Boston: Focal Press, 1990. Offers a contemporary examination of the technological history of the mass media. Chapter 3 provides a fine overview of the history of FM radio, including Armstrong’s contributions.
  • citation-type="booksimple"

    xlink:type="simple">Lessing, Lawrence. Man of High Fidelity: Edwin Howard Armstrong. New York: J. B. Lippincott, 1956. Paints a portrait of Armstrong as a great man who, against the odds, was able to convince a nation to adopt FM radio broadcasting.
  • citation-type="booksimple"

    xlink:type="simple">Lichty, Lawrence W., and Malachi C. Topping, comps. American Broadcasting: A Source Book on the History of Radio and Television. New York: Hastings House, 1975. Collection of articles and documents concerning the history of radio and television. Treats the invention and innovation of FM radio transmission in some detail.
  • citation-type="booksimple"

    xlink:type="simple">Sterling, Christopher H., and John Michael Kittross. Stay Tuned: A History of American Broadcasting. 3d ed. Mahwah, N.J.: Lawrence Erlbaum, 2001. The standard one-volume history of radio and television in the United States. Provides particularly strong coverage of the history of FM radio broadcasting.
  • citation-type="booksimple"

    xlink:type="simple">Whetmore, Edward Jay. The Magic Medium: An Introduction to Radio in America. Belmont, Calif.: Wadsworth, 1981. Fine textbook covers all phases of radio, including Armstrong’s invention and attempted innovation of FM radio. Places Armstrong’s role in the history without the “wronged man” rhetoric found in other accounts.

Radio Develops as a Mass Broadcast Medium

Radio Broadcasting Begins

National Broadcasting Company Is Founded

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