Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from A-E

Armstrong, Edwin Howard (1890-1954)

armstrong’s radio signal modulation

Millions of radio listeners each day tune in their favorite FM (i.e., frequency modulation) stations to hear crystal clear, high-fidelity music and other programming. FM radio offers clarity and a dynamic range that cannot be matched by AM (i.e., amplitude modulation) broadcasting. Many people cannot explain how the signals reach their radios or why the FM stations sound so much better than their AM equivalents. However, if people enjoy the programming that FM stations provide, then they owe a debt of gratitude to the inventor of the technology that made it all possible: Edwin Howard Armstrong.

Armstrong was born on December 18, 1890, in New York City, the first child of Emily and John Armstrong. Young Edwin grew up in a family that was well to do, well educated, and a cornerstone of their Yonkers, New York, community. A quick mind was highly valued in the Armstrong household, as well as a strong body. John Armstrong taught his children the game of tennis, which Edwin would retreat to later in life as a reprieve from his struggles in the laboratory.

Armstrong developed his interest in wireless telephony from books that his father brought back from annual business trips to London. He was fascinated by the tales of inventors such as Guglielmo Marconi and his efforts to send wireless signals across the Atlantic. Soon, with the help of a family friend, Armstrong was building his own wireless apparatus in the attic and communicating with other young boys who were bitten by the wireless “bug.”

The long hours in his attic continued throughout his childhood and through adolescence. Upon graduation from Yonkers High School, Armstrong set out for Columbia University and its prestigious program in electrical engineering; however, the tinkering in the attic never ceased. Armstrong’s professors recognized his brilliant mind, but his dedication to coursework paled in comparison with his love of the laboratory.

In 1912, with the help of Professor John More-croft, Armstrong began investigating the properties of the audion tube, a tri-element vacuum tube invented by Lee De Forest that was used to detect an electromagnetic signal. Even De Forest himself, however, was unclear as to how the audion worked. Armstrong discovered, according to Tom Lewis (1991, p. 70), that “[the] audion was essentially a device that relayed electrons.… Acting on this discovery, Armstrong then thought of feeding the oscillating current from the plate back into the grid circuit to have it amplified over again.” The result, in September 1912, was Armstrong’s first invention: the regenerative circuit.

As was often the case in this era of invention, Armstrong’s invention was challenged in the courts. De Forest claimed to have invented the regenerative circuit in 1912, a year before Armstrong had applied for his patent. After several early convincing victories for Armstrong in the courts, many felt that De Forest was “throwing in the towel” when he requested a license to manufacturer the regenerative circuit. However, convinced that De Forest had attempted to steal his invention, Armstrong blocked the request. While Armstrong’s focus and determination had served him well as an attic inventor, his stubbornness in his dealings with De Forest cost him dearly. De Forest continued his interference application in the U.S. Patent Office, won a few key victories, and finally, in 1934, had his claim as the inventor of the regenerative circuit upheld by the U.S. Supreme Court. Although the courts named De Forest the victor, most of the radio engineering community maintained Armstrong as the true founder of regeneration. At the 1934 meeting of the Institute of Radio Engineers (IRE), Armstrong attempted to give back a Medal of Honor that he had received years earlier from this organization for his work in relation to regeneration. The board of directors of the IRE refused to take back his medal and instead publicly affirmed the spirit of their original citation.

Armstrong’s greatest accomplishment, however, was yet to come. For years, radio engineers had struggled with the static associated with an AM signal. Attempts at solving this problem included increased amplification (increasing noise at the same time) and restricting the frequency range of the signal (resulting in a loss of fidelity). All of these attempts, however, were made with the existing transmission method of amplitude modulation. Armstrong’s approach to this significant problem typified his innovative style. He broke from traditional theory and experimented with an entirely new system of broadcasting: frequency modulation.

In brief, radio signals are piggybacked on a carrier wave, which is an electromagnetic signal that is characterized by consistent wave height (amplitude) and cycles per second (frequency). From the beginning, radio stations were transmitting their information by amplitude modulation, wherein the frequency is kept constant while the height of the wave is adjusted. Armstrong thought that frequency modulation (adjusting the cycles per second rather than the height of the wave) might hold the key to the elimination of static.

Others had experimented with frequency modulation as a transmission method; however, none had attempted to change the whole system, from transmitter to receiver. Some, including noted theoretical mathematician John Carson, thought static would always be a part of radio. Armstrong, with help of assistants Thomas Styles and John Shaughnessy, set about creating this new system by confronting one of the key principles of traditional AM broadcasting: narrow bandwidth.

Bandwidth is the space a signal occupies when it is imposed upon a carrier wave. A wide bandwidth can carry a better signal, but it also is more susceptible to interference. The solution to this interference, in the AM model, was to narrow the bandwidth, thus reducing the noise in the transmission. When early experiments with frequency modulation applied this commonly held principle of narrow bandwidth, static was not reduced. The result was that many scientists abandoned FM as a viable transmission method, but Armstrong believed that widening the bandwidth could dramatically improve the signal-to-noise ratio.

The key component of Armstrong’s system was his ingenious receiver that captured the FM signal, amplified it, strained out amplitude variations, converted the signal to amplitude modulation, and prepared it for conversion to acoustic energy through a loudspeaker. Armstrong received multiple patents for this new system in 1933 and it was publicly demonstrated for the first time at the Institute of Radio Engineers meeting in New York City on November 5, 1935. According to Lawrence Lessing (1956), the demonstration went off without a hitch, transmitting music and other sounds at fidelity not heard before. Not only did the “wide band” FM system offer improved quality, it operated with much less power than a typical AM transmitter. Business reality, however, kept Armstrong’s innovation from being adopted immediately.

In 1935, the Radio Corporation of America (RCA) was heavily invested in the existing AM broadcasting system, owning every major patent. In addition, they were also spending millions of dollars to develop what they believed to be the next great innovation in broadcasting: television. Both FM and television were completely new systems and RCA was reluctant to ask the public and broadcasters to invest in two new technologies at once. Nevertheless, it was not only industry powers that halted the advance of FM. The Federal Communications Commission (FCC) waited until March 1940 before they authorized FM broadcasting. Armstrong was further thwarted by World War II, which delayed the construction of new FM stations until 1946.

The final blow for Armstrong came from his former friend, David Sarnoff, and RCA. In the early 1950s, RCA, in an attempt to circumvent Armstrong’s patents, claimed to have invented an FM broadcasting system superior and markedly different from Armstrong’s. This set in motion litigation that lasted more than a decade and led to the ultimate unraveling of Edwin Armstrong’s life. His fortune, amassed from royalty payments from his previous patents, dwindled during this court battle. His marriage of some thirty years to his wife Marion was crumbling while he obsessed with professional redemption. Finally, after rejecting a settlement proposal from RCA, and with his wife away with her sister in Connecticut, Armstrong committed suicide on January 31, 1954, by jumping from the window of his thirteenth-floor apartment in New York City.

Unfortunately, Armstrong did not live to see the fruits of his greatest invention and his final victory in the courts. FM listenership expanded greatly in the 1960s and 1970s, in large part because of the demand for the high-fidelity stereo sound that only FM broadcasting could deliver. By 1980, the audience for FM stations was larger than the one for AM stations, and by the end of the 1990s, FM stations were attracting more than 80 percent of the radio listeners.

Possibly because of the tragic nature of his death, Armstrong’s fame has never been commensurate with the influence that he had on the communication industry. However, while he may never be a household name, the effect that he had on the radio industry will last forever.

Armstrong, Karan [next] [back] Armstrong, Edwin Howard

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

over 7 years ago