Where can I find historical data on radio towers and radio stations in the United States? For example, the latitude/longitude, tower height, and transmitting power of every tower that existed in 1930, 1940, etc.?
Alternatively, are there datasets of historical coverage of radio stations? As in, for a certain latitude/longitude, all the radio stations that they (may have) received as of a certain date? The historical element is very important here. I'm not looking for recent data or data after 1970.