COMMERCIAL radio broadcasting in the United States began just fifty years ago, in 1920. By 1925 there were 3 million radios in American homes. By 1940 these had increased to over 45 million, and now there are an estimated 275 million radios in the United States. That is more than one radio per person! Yet, despite their number, most persons understand little about a radio’s operation. Have you ever wondered how it works?