A pioneer in radio technology, Edwin H. Armstrong invented wide-band frequency modulation (known popularly as "FM") of radio waves. Even before developing FM, Armstrong developed the feedback circuit in 1912. Feedback, or regenerative, circuitry permitted the development of amplifiers. Work on that circuit placed him at odds with Lee De Forest, which resulted in a 12-year legal suit. De Forest prevailed and Armstrong later donated $50,000 to Columbia University for study on how the courts are able to decide complex technical questions. In 1918, he developed the superheterodyne circuit, which is the basis of contemporary amplitude modulation (AM) radio receivers. He also invented the multiplexing system, which permits broadcasting more than one program on the same frequency.