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Professional and personal files including Armstrong's correspondence with professional associations, other engineers, and friends, his research notes, circuit diagrams, lectures, articles, legal papers, and other related materials. Of his many inventions and developments, the most important are: 1) the regenerative or feedback circuit, 1912, the first amplified radio reception, 2) the superheterodyne circuit, 1918, the basis of modern radio and radar, 3) superregeneration, 1922, a very simple, high-power receiver now used in emergency mobile service, and 4) frequency modulation - FM, 1933, static-free radio reception of high fidelity. More than half the files concern his many lawsuits, primarily with Radio Corporation of America, over infringement of the Armstrong patents. Litigation continued until 1967. Other files deal with his work in the Marcellus Hartley Research Laboratory at Columbia University, 1913-1935, and with the American Expeditionary Forces in France during World War I, his Air Force contracts for communications development, Army research during World War II, the Radio Club of America, the Institute of Radio Engineers, FM development at his radio station at Alpine, N.J., the use of FM in television, his involvement in Federal Communications Commission hearings and legislation, and his work with the Zenith Radio Corporation. Also, letters to H.J. Round

Correspondence relating to Erskine's various educational, musical and literary interests; manuscripts of his writings; lecture notes for college courses; souvenirs of his army service in World War I and his Columbia University professorship, and student papers from his own school and college days. Also, biographical file, scrapbooks, and articles.

Correspondence, notes, and writings of Sayre, including materials pertaining to his work for various organizations, public and private, concerned with problems in public administration. There is also a subject file containing notes and other materials gathered by Sayre for use in publications and lectures. The correspondence is extensive, and consists of routine business correspondence, occasional letters (uncataloged) from such persons as William Ronan and other city and university officials, and files of correspondence with members of the family of Senator Robert M. La Follette. Catalogued correspondents include Chester Bowles, Dumas Malone, Bennett Cerf, and Fiorello La Guardia.