Edwin Howard Armstrong, the “Radio Boy,” and the Creation of FM

January 28, 2023 by Chantelle Dubois

With a lifelong passion for radio, Edwin H. Armstrong is credited with creating frequency modulation (FM), the standard for radio broadcast today.

Edwin Howard Armstrong was the so-called Radio Boy, an American engineer who spent his childhood building antenna towers in his backyard and conducting experiments in his attic. 

Armstrong was born just before the turn of the century in 1890 in Chelsea, New York City, and grew up comfortably in a middle-class household. He was inspired by Guglielmo Marconi, who sent the first wireless message across the Atlantic Ocean, and his early readings of Marconi’s exploits instilled a great appreciation of radio in the impressionable young Armstrong.


Edwin Howard Armstrong

Focusing on his brilliance and contribution to radio, here is a spotlight on historical engineer Edwin Howard Armstrong. Image used courtesy of Columbia University


The rest of his life would be a combination of triumphs and tragedies. Armstrong made many significant contributions to radio with 42 patents, including for Frequency Modulation (FM). While he ultimately became wealthy enough to fund his own research, he spent a non-trivial part of his time fighting legal battles and lobbies against his technologies. His legal and later financial and marriage troubles would accumulate to Armstrong taking his own life at the age of 63 in 1954.

Unfortunately, Armstrong didn't live to see his FM technology go on to become the de facto standard for radio broadcast. 


Improving Lee de Forest's Audion

Armstrong was admitted to Columbia University’s department of electrical engineering in 1909 and became a mentee of Professor Michael Pupin, a founding member of the National Aeronautics and Space Administration. 

During Armstrong’s early years in his studies, he became interested in the audion, a triode vacuum tube invented by American engineer Lee de Forest in 1906. At the time of its invention, the audion was seen as not much more than a slight improvement on the Fleming valve. The audion could receive and amplify weak signals but did so only marginally and was not otherwise particularly groundbreaking.

Armstrong fixated on understanding how the audion worked and performed various calculations and measurements to figure out how to make it useful. Before Armstrong’s senior year, he determined it was possible to amplify weak signals by creating a positive feedback loop. This suddenly made the audion very useful as a radio receiver; it could now amplify radio signals to make them audible to an entire room.


An audion tube

An audion tube. Image used courtesy of Paul Thompson


Armstrong moved quickly to patent what he called a “regenerative receiver” in 1913 and provided a demonstration at a conference organized by the Institute of Radio Engineers (IRE) at Columbia. It turned out de Forest was in the audience, and not long after, de Forest claimed that he was, in fact, the inventor of regeneration using the audion. Lee de Forest then filed a patent that would interfere with Armstrong’s. This offset Armstrong’s first brush with legal woes against de Forest that would last decades. 

Armstrong received recognition for the regenerative receiver, including an IRE Medal of Honor, the Franklin Medal, and the Edison Medal. He would ultimately lose his legal fight with de Forest due to legal technicalities, although it was broadly understood and accepted by the technical community that Armstrong was the true inventor. When Armstrong tried to return his IRE Medal of Honor at a convention, it was refused. 


World War I and the Superheterodyne Receiver

After completing his degree in electrical engineering in 1913, Armstrong accepted a position as an assistant at Columbia University. Then not long later, he would be sent to Paris during World War I as part of the U.S. Army Signal Corps to work on radio communication.

One of Armstrong’s projects was to improve the interception of enemy short-wave communication. During his efforts, he invented what would become known as the superheterodyne radio receiver. The receiver enabled a radio set to mix incoming radio signals with an internally-generated signal to create a more manageable intermediary frequency that could be filtered. 


Armstrong’s prototype of the superheterodyne receiver

Armstrong’s prototype of the superheterodyne receiver. Image used courtesy of Radio Amateur News


This invention made Armstrong a millionaire by selling the patent to Westinghouse. Once again, there would be legal disputes about Armstrong’s patent, although to a lesser degree than he experienced with the regenerative receiver. 

When Armstrong returned to the U.S., he rejoined Columbia—this time, without accepting a salary. Instead, he funded his own research to avoid administrative and teaching work. After his mentor Pupin retired, Armstrong took over his professorship at the university.


Frequency Modulation

Some of Armstrong’s work with Pupin focused on a problem with static in Amplitude Modulation (AM) radio broadcasts. At the time, AM was the standard method of radio transition that involved modulating the amplitude of a signal to transmit information. However, because AM is sensitive to distortion and interference, the weather or other atmospheric conditions could have a significant impact on the clarity of radio broadcasts.

Frequency modulation appeared to be a more robust option since the frequency is changed instead of the amplitude. Although Armstrong was not the first to theorize this point, he made the first attempt to develop hardware to demonstrate its capability. There was not much competition to advance FM since it was not considered advantageous over AM.


The difference between AM and FM frequency

The difference between AM and FM frequency. Image used courtesy of Science ABC


One of Armstrong’s specific achievements was the use of wide-band FM; before that, it was believed that FM was only practical as narrow-band FM. Armstrong invested his own money to build a wide-band FM transmitter and receiver. Once again, at an IRE conference, he gave a demonstration where he had a friend in Yonkers, New York, transmit audio to Armstrong’s receiver at the conference. There, he demonstrated a radio broadcast free of static, with high-fidelity audio of various sounds, including tearing paper and water being poured. 

Despite this demonstration, FM was being buried as quickly as possible. There was resistance to the technology due to the already existing AM infrastructure and both radio and television broadcasting industries not having an interest in making the transition. 

Armstrong was resolute in his belief in the advantages of FM and continued to pour his money and time into the technology. He was denied opportunities to advance FM at every corner, including when the Federal Communications Commission refused to grant him an experimental license for an FM station. At the same time, his legal battles over patents continued, and his marriage was experiencing trouble.  

Armstrong’s life had some incredible highs but ended with an incredible low, leaving behind his wife and daughter. His wife continued his legal fights on his behalf and would win some and settle others.