THE FIRST DJ: Reginald A. Fessenden

To me, the first DJ is the first person to broadcast voice and music over the radio and for more than one person to hear it —a true radio broadcast. It has been reported that he developed this while working for the national Weather Service But that's only if you believe one of the founding myths of radio. [More here]

If you beleive it, in an epic moment in 1900 on Christmas Eve, Fessenden transmitted the first radio broadcast in history from Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing the song "O Holy Night" on the violin and then reading a passage from the Bible. That happened at Cobb Island in Maryland in December of 1900. His job there was to set up telegraph connections for collecting remote weather observations. Like a true geek he instead used the time and effort to explore and actually produce voice over radio. But only one person received these test signals, his unnamed assistant. This was not a broadcast. This was more analogous to the Marconi experiments of 1901. 

In 1906, Fessenden repeated the experiential voice transmission by radio between Scotland and Massachusetts. The New York Times reported on this event and it remains his earliest verifiable broadcast. Like many geniuses the potential for his inventions was not recognized early on and even his own investors weren't interested. He claimed distances of over 200 miles were possible. His work with the National Electric Signaling Company (NESCO) seems to have been rocky. He was fired in 1911. He claimed to be owed money. A lengthy lawsuit followed.

Did I mention he discovered the Heterodyne principle? By fixing the beat frequency between the incoming carrier and the local oscillator to a fixed intermediate frequency (IF), most of a radio receiver can be constructed so that it can be used by any incoming radio signal. Only the local oscillator is tuned to produce a beat frequency equal to the fixed IF frequency. Before this development, a radio could only be used on ONE FREQUENCY in sending or receiving.