On the night of September 22, 1912, while working alone in the attic of his boyhood home, Armstrong perfected the process of electronic regeneration. Using an audion tube, Armstrong discovered that he could feed the incoming radio signal back into the tube again and again, as many as 20,000 times, thus greatly amplifying the signal and making the reception of far-off stations practical. The practice of regeneration is still a basic of electronics. Unfortunately, Lee de Forest was able to gain patent rights to the system through a legal technicality. If you wish to learn more about the struggle between de Forest and Armstrong, have a look at Empire of the Air by Tom Lewis or the PBS video of the same name. See: http://www.invent.org/book/book-text/3.html