When did Edwin Howard Armstrong invent the FM radio?
According to a recent book (Early FM Radio, by Frost), modern FM wasn't invented all at once, but evolved with the help of dozens of other people besides Armstrong. But Armstrong was the first to significantly widen the frequency swing. A hand-drawn sketch indicates that he hit on that idea in the summer of 1932. During the following January he filed two patent applications for wide-band FM, one of which has a similar sketch. On December 26, 1933, he was awarded four patents for FM radio (The other two were applied for in 1927 and 1930, but weren't for wide-band). He discovered in early 1934 that his invention was almost free of static.Armstrong took a few more years to give FM high fidelity, but by 1938 or 1939 he had improved FM to the point that it was our FM radio, minus the stereo sound.