Tag Archives: regenerative circuit

Early Childhood and College Years….

Born in 1890, in the Chelsea district of Manhattan, E. H. Armstrong was the first child of John and Emily Armstrong. He had two younger sisters, Ethel and Edith, and in 1902 the family moved out of New York City to 1032 Warburton Avenue in Yonkers, New York. The house was a large Victorian overlooking the Hudson River.

E. H. Armstrong home at 1032 Warburton Avenue, Yonkers, New York, undated


house at 1032 Warburton Avenue, Yonkers, New York, as seen behind radio pole, undated

During his childhood summers, the family usually left Yonkers and stayed at a farm in upstate New York. John Armstrong was an avid tennis player and set up tennis courts where the young Major quickly honed his talents.

E. H. Armstrong holding a trophy (tennis) with unidentified individual, undated


Edwin’s father gave him a book "The Boys Book of Inventions" which had a huge impact on the young boy. He studied Michael Faraday and Gugliemo Marconi and set out to become an inventor, more specifically, a wireless inventor. He set up wireless apparatus in the attic and soon made friends with numerous boys in and around the neighborhood, all of which had an interest in wireless communications.  His early cohorts, whom he remained friends with for the duration of his life, were Bill Russell, Tom Styles, and Randy Runyon.


E.H. Armstrong with sister’s Edith and Ethel, undated

Armstrong built an antenna mast on his lawn. His youngest sister Edith, or Cricket as Armstrong had nicknamed her, acted as his sole assistant in this project.  


125 foot radio pole at 1032 Warburton Avenue, Yonkers, New York, undated












In 1909, he entered the undergraduate electrical engineering program at Columbia University. He undertook endless experiments, learning from various professors that nothing should be taken for granted. He soon took to Professor Michael Pupin, one of the founders of Columbia’s Department of Electrical Engineering and head of the Marcellus Hartley Research Laboratory.

Pupin had been working on improving wireless transmission, as had Armstrong, up in his attic at 1032 Warburton Avenue. Pupin noticed the young genius in his tireless pursuit of strengthening wireless transmissions. In 1912, Armstrong told his friend and classmate, Herman Burgi, he had discovered a method of amplifying wireless signals. It would not be until 1913, when Armstrong had the money to file for the patent, that he would debut his regenerative circuit.

I came upon many of Armstrong’s undergraduate "labs" for both electrical engineering and mechanical engineering classes. I have included an example of one below.

Armstrong and Burgi undergraduate "lab" for mechanical engineering, 1912, cover page


Armstrong and Burgi undergraduate "lab" for mechanical engineering, 1912, interior page












Armstrong and Burgi undergraduate "lab" for mechanical engineering, 1912, interior page





Armstrong and Burgi undergraduate "lab" for mechanical engineering, 1912, interior page











In addition to a variety of undergraduate "labs", I came upon an early notebook which is unfortunately undated. On the interior of the front cover Armstrong lists himself as the rightful owner and should the notebook get lost, a reward for its return. You will also see some of the interior pages, including the index and his investigation into the audion.

Armstrong Notebook, undated









Armstrong Notebook, interior of cover, undated






Armstrong Notebook, Index, undated


Armstrong Notebook, interior page 51








Armstrong Notebook, page 75


Armstrong Notebook, page 92


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.