Tag Archives: Institute of Radio Engineers

The Superheterodyne

When the United States entered World War I, Armstrong enlisted in the Signal Corps. In 1917 he was posted to France, placed in charge of the Radio Group of the Research Section of the Division of Research and Inspection. This Division had been created in order to examine any existing equipment manufactured by the Europeans for the American Expeditionary Forces.                                              

Round, Henry Joseph, 1960

The Major set off to France but en route he was delayed in England due to heavy fog. While there, he ventured to London, stopping by the Marconi offices. The letter seen here (below), dated 1917 October 28, from Armstrong to his mother, details his visit and recounts his introduction with Henry Joseph Round.

EHA letter to Mother, 1917 October 28, first 2 pages



EHA letter to Mother, 1917 October 28, last 2 pages



Round was an engineer with Marconi who, at the time, was in charge of the Admiralty’s wireless direction-finding stations. It was here that Armstrong was introduced to Round’s short-wave equipment. Round had created these amplifiers by designing his own vacuum tube (V24). These tubes were not, and would never be, available to the French and the Americans, as these tubes were not appropriate for the task. Armstrong’s attention was captured as this was a problem that required further research. 

 Armstrong had studied heterodyne circuitry for quite a while and understood it well. This meeting with Round pushed him further and he continued to examine the problem of receiving weak high frequency signals. As the Major recounts some years later upon receiving the Edison Medal in 1943:

"The third link came months later as I happened to be watching a night bombing raid and wondered at the ineffectiveness of the antiaircraft fire. I may say that night bombing was not very dangerous in those days, either for the man on the ground or the man in the airplane. Thinking of some way of improving the methods of locating the position of airplanes, I conceived the idea that perhaps very short waves sent out from them by the motor ignition systems might be used. The unique nature of the problem, involving the amplification of waves shorter than any ever contemplated and quite insoluble by any conventional means of reception, demanded a radical solution. All three links of the chain suddenly joined up and the superheterodyne method of amplification was practically forced into existence. Not one link in the chain could have been dispensed with. This, I think is the only completely synthetic invention I have ever made." 1

The bombing raid and third link, to which Armstrong refers above, occurred in Paris, March 1918. He had thus sorted out how to use the heterodyne principle to bring short-wave frequencies down to the range of his long-wave amplifier. He worked out the necessary experiments needed to prove his forthcoming invention, writing down the proposed method in June 1918 with Major Buckley signing off as witness (proposal seen here in 3 pages).

Method of Reception, Disclosed to Major O.E. Buckley, 1918 May-June, page 1


Method of Reception, Disclosed to Major O.E. Buckley, 1918 May-June, page 2










Method of Reception, Disclosed to Major O.E. Buckley, 1918 May-June, page 3

Following Armstrong’s proposed methodology to Major Buckley, experiments would need to be conducted. Armstrong needed assistance to stage these experiments and create the necessary apparatus. With war work taking precedence and his fellow officers tied up in other pressing projects, his work was delayed. The first model was not ready until November. Armstrong first applied for patent in France in December 1918 and for United States patent in February 1919.

When Armstrong returned from the war he presented his paper, "A New System of Short Wave Amplification," to the Institute of Radio Engineers in December of 1919, delineating his new receiver.

In 1920, Westinghouse purchased Armstrong’s regeneration and superheterodyne patents. Also, around this time, AT & T purchased Lucien Levy’s patent for essentially, the same invention. Originally Levy’s patent covered a different purpose than did Armstrong’s resulting in the US Patent Office not catching the conflict. Someone eventually noticed this apparent conflict and priority needed to be resolved.

The Court of Appeals in the District of Columbia ruled in Levy’s favor and his patent was issued on November 5, 1929, with a priority date of August 4, 1917 (he had filed 6 months prior to Armstrong). While Levy, by law, is considered the inventor of the superheterodyne method, Armstrong is recognized as bringing about its commercialization through the single tuning knob superhet receiver.



1-Armstrong, Edwin H. "Vagaries and Elusiveness of Invention," Electrical Engineering 62 (April 1943).

Additional Information regarding superheterodyne patent:

Schottky, Walter  "On the Origin of the Super-Heterodyne Method," Proceedings if the IRE, Vol. 14, No. 5, 695-698 (October 1926)

Armstrong, Edwin H. "A New System of Short Wave Amplification," Proceedings of the IRE, Vol. 9, No. 1, 3-27 (February 1921)

Douglas, Alan S. "Who Invented the Superheterodyne?," Proceedings of the Radio Club of America, Inc., Vol. 64, No. 3, 123-142 (November 1990)

The Regenerative Circuit

Listening to the radio now, as I do quite often, I never would have imagined the difficulties that plagued it in the past. Although not yet around to experience early radio listening first hand, I have read enough to understand just how close one would have had to have been to the speaker. In fact, headphones were generally required. It was here at Columbia University during his undergraduate study that Armstrong made his first momentous discovery, the regenerative circuit, eliminating the need for headphones and providing the foundation of many radio receivers that followed.


Improved Audion Receiver, 1914 January 14

Improved Audion Receiver, 1914 January 14
In 1906, Lee de Forest created the "audion," an early vacuum tube. He had added a third element, the grid, to the Edison-Fleming diode. Subsequently, in 1912, he accidentally connected the output circuit of one audion to its own input circuit and obtained a loud howling sound,which he later identified as regeneration. But instead of attempting to understand this hissing or howling sound, he tried to abolish it.  A modern day example of this phenomenon results when a microphone is placed too close to its accompanying speaker, resulting in an uncomfortable noise (feedback).
When Armstrong began experimenting with the audion, he took numerous measurements in order to figure out how this tube functioned, eventually devising a circuit that would operate as a powerful amplifier of  incoming radio waves (E. H. Armstrong drawing above on left). He figured out that if part of the plates output current was fed back to the grid in a controlled manner, the incoming signals were remarkably strengthened . In addition, he discovered that when feedback was increased sufficiently the circuit could be used as a transmitter by generating high frequency oscillations, a required element for radio communications (E. H. Armstrong drawing below).

Circuits for Using the Audion as a Generator of High Frequency Oscillations, 1914 March 13

Circuits for Using the Audion as a Generator of High Frequency Oscillation, 1914 March 13
Armstrong’s invention led to a nearly twenty-year legal battle over patent rights. Between 1914 and 1934, he and de Forest fought in court both individually and through the corporations (Westinghouse Electric and American Telephone and Telegraph, respectively) who had purchased rights to their patents. Long and complicated, the battle began when de Forest sat in the audience listening to one of Armstrong’s lectures on the transmitting and receiving properties of his regenerative circuit. Although de Forest had given lectures in 1913 on the qualities of his audion invention, he never claimed it retained any of the capacities that Armstrong had discovered.  de Forest went on to submit a claim to the same invention in 1914, but the courts upheld Armstrong as the patent owner for the next ten years. It ended in 1934 when the Supreme Court decided in de Forest’s favor.
Regardless of the Supreme Court’s decision, the engineering community still recognizes Armstrong as the rightful inventor and has given him multiple awards for it. In 1917, the Institute of Radio Engineers (IRE) awarded him their Medal of Honor and in 1942, the American Institute of Electrical Engineers (AIEE) awarded him the Edison Medal, the highest award of the Institute (In 1963, the IRE and the AIEE merged to form the IEEE (Institute of Electrical and Electronics Engineers). These prestigious awards still stand today.
The original early drawings seen here, along with extensive litigation files, can be found within the Edwin H. Armstrong collection.