Armstrong's third great discovery - the superregenerative circuit.
RCA, having missed the opportunity to purchase Armstrong's feed-back and superheterodyne patents, and having to later pay Westinghouse dearly for them, would not miss this one. On June 30, 1922, RCA paid Armstrong $200,000.00 plus 60,000 shares of RCA stock (then worth $217,500.00). The deal included giving RCA first right of refusal on any future inventions.
These are several selected pages from his draft of the first public disclosure, read before the IRE on June 7th 1922 and published in the August 1922 Proceedings of the IRE.