English: American electrical engineer and inventor Edwin H. Armstrong in 1922. Armstrong is one of the most prolific inventors in the history of radio. He invented the regenerative circuit (vacuum tube feedback oscillator), the superregenerative receiver, the superheterodyne receiver, and frequency modulation (FM) radio transmission. This was probably taken at the June 28, 1922 meeting of the Radio Club of America in room 306, Havemeyer Hall, Columbia University, New York, at which Armstrong demonstrated the superregenerative receiver. his prototype is partially visible on the right.