receiving system

Edwin Howard Armstrong


Edwin Howard Armstrong (December 18, 1890January 31, 1954) was an American electrical engineer and inventor. Armstrong was the inventor of frequency modulation (FM) radio.

Birth and education

Edwin Howard Armstrong was born in New York City, New York, in 1890. He studied at Columbia University and later became a professor there. He invented the regenerative circuit while he was an undergraduate and patented it in 1914, the super-regenerative circuit (patented 1922), and the superheterodyne receiver (patented 1918).

Work and patent disputes

Many of Armstrong's inventions were ultimately claimed by others in patent lawsuits. In particular, the regenerative circuit, which Armstrong patented in 1914 as a "wireless receiving system," was subsequently patented by Lee De Forest in 1916; De Forest then sold the rights to his patent to AT&T. Between 1922 and 1934, Armstrong found himself embroiled in a patent war, between himself, RCA, and Westinghouse on one side, and De Forest and AT&T on the other. At the time, this action was the longest patent lawsuit ever litigated, at 12 years. Armstrong won the first round of the lawsuit, lost the second, and stalemated in a third. Before the Supreme Court of the United States, De Forest was granted the regeneration patent in what is today widely believed to be a misunderstanding of the technical facts by the Supreme Court.

FM radio

Even as the regenerative-circuit lawsuit continued, Armstrong was working on another momentous invention. While working in the basement lab of Columbia's Philosophy Hall, he created wide-band frequency modulation radio (FM). Rather than varying the amplitude of a radio wave to create sound, Armstrong's method varied the frequency of the wave instead. FM radio broadcasts delivered a much clearer sound, free of static, than the AM radio dominant at the time. (Armstrong received a patent on wideband FM on December 26, 1933; his just rewards required much litigation at the end of his life, and beyond it.)

In 1922, John Renshaw Carson of AT&T, inventor of Single-sideband modulation (SSB modulation), had published a paper in the Proceedings of the Institute of Radio Engineers (IRE) arguing that FM did not appear to offer any particular advantage . Armstrong managed to demonstrate the advantages of FM radio despite Carson's skepticism in a now-famous paper on FM in the Proceedings of the IRE in 1936 , which was re-printed in the August 1984 issue of Proceedings of the IEEE .

Today the consensus regarding FM is that narrow band FM is not so advantageous in terms of noise reduction, but wide band FM can bring great improvement in signal to noise ratio if the signal is stronger than a certain threshold. Hence Carson was not entirely wrong, and the Carson bandwidth rule for FM is still important today. Thus, both Carson and Armstrong ultimately contributed significantly to the science and technology of radio. The threshold concept was discussed by Murray G. Crosby (inventor of Crosby system for FM Stereo) who pointed out that for wide band FM to provide better signal to noise ratio, the signal should be above a certain threshold, according to his paper published in Proceedings of the IRE in 1937 . Thus Crosby's work supplemented Armstrong's paper in 1936.

Armstrong conducted the first large scale field tests of his FM radio technology on the 85th floor of RCA's (Radio Corporation of America) Empire State Building from May 1934 until October 1935. However RCA had its eye on television broadcasting, and chose not to buy the patents for the FM technology. A June 17, 1936, presentation at the Federal Communications Commission (FCC) headquarters made headlines nationwide. He played a jazz record over conventional AM radio, then switched to an FM broadcast. "[I]f the audience of 50 engineers had shut their eyes they would have believed the jazz band was in the same room. There were no extraneous sounds," noted one reporter. He added that several engineers described the invention "as one of the most important radio developments since the first earphone crystal sets were introduced."

In 1937, Armstrong financed construction of the first FM radio station, W2XMN, a 40 kilowatt broadcaster in Alpine, New Jersey. The signal (at 42.8 MHz) could be heard clearly 100 miles (160 km) away, despite the use of less power than an AM radio station.

RCA began to lobby for a change in the law or FCC regulations that would prevent FM radios from becoming dominant. By June 1945, the RCA had pushed the FCC hard on the allocation of electromagnetic frequencies for the fledgling television industry. Although they denied wrongdoing, David Sarnoff and RCA managed to get the FCC to move the FM radio spectrum from (42-50 MHz), to (88-108 MHz), while getting new television channels allocated in the 40 MHz range.

This single FCC action rendered all Armstrong-era FM sets useless overnight, and protected RCA's AM-radio stronghold. Armstrong's radio network did not survive the frequency shift up into the high frequencies; most experts believe that FM technology was set back decades by the FCC decision. This change was strongly supported by AT&T, because loss of FM relaying stations forced radio stations to buy wired links from AT&T.

Furthermore, RCA also claimed invention of FM radio and won its own patent on the technology. A patent fight between RCA and Armstrong ensued. RCA's momentous victory in the courts left Armstrong unable to claim royalties on any FM radios sold in the United States. The undermining of the Yankee Network and his costly legal battles brought ruin to Armstrong, by then almost penniless and emotionally distraught.


Alone and driven to despair over the FM debacle, Armstrong, dressed in full coat and hat, jumped to his death from the thirteenth floor window of his New York City apartment on January 31, 1954. His suicide note to his wife said: "May God help you and have mercy on my soul". His widow Marion, who had been Sarnoff's secretary before marrying Armstrong, renewed the patent fight against RCA and finally prevailed.


It took decades following Armstrong's death for FM broadcasting to meet and surpass the saturation of the AM band, and longer still for FM radio to become profitable for broadcasters. Armstrong was of the opinion that anyone who had actual contact with the development of radio understood that the radio art was the product of experiment and work based on physical reasoning, rather than on the mathematicians' calculations and formulae (known today as part of "mathematical physics").


In 1917 Armstrong was the first recipient of the IRE's, now IEEE Medal of Honor. For his wartime work on radio the French government gave him the Legion of Honor in 1919. He received in 1942 the AIEEs Edison Medal "For distinguished contributions to the art of electric communication, notably the regenerative circuit, the superheterodyne, and frequency modulation". The ITU added him to its roster of great inventors of electricity in 1955. In 1980 he was inducted into the National Inventors Hall of Fame, and was on a U.S. postage stamp in 1983. The Consumer Electronics Hall of Fame inducted him in 2000, "in recognition of his contributions and pioneering spirit that have laid the foundation for consumer electronics."

Philosophy Hall, the Columbia building where Armstrong developed FM, was declared a National Historic Landmark in 2003 in recognition of that fact. Armstrong's home in Yonkers also received a similar designation, but it was withdrawn when the house was later demolished.

See also

  • Armstrong Tower : tall lattice tower built and used by Edwin Armstrong in 1938.


Armstrong received 42 patents in total; a selection are listed below:

  • : "Electric Dynamo and Motor"
  • : "Wireless Receiving System"
  • : "Electric Wave Transmission" (Note: Co-patentee with Michael I. Pupin)
  • : "Antenna with Distributed Positive Resistance"
  • : "Method of Receiving High Frequency Oscillation"
  • : "Selectively Opposing Impedance to Received Electrical Oscillations" (Note: Co-patentee with M. I. Pupin)
  • : "Signaling System"
  • : "Wireless Receiving System for Continuous Wave"
  • : "Radio Signaling System" (Note: This is one of the patents issued for wideband FM in 1933.)
  • : "Radiosignaling" (Note: This is one of the patents issued for wideband FM in 1933.)
  • : "Radiosignaling" (Note: This is one of the patents issued for wideband FM in 1933.)

References and notes

Further reading

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