Alexanderson Alternator

An Alexanderson alternator is a rotating machine invented by Ernst Alexanderson in 1904 for the generation of high frequency alternating current up to 100 kHz, for use as a radio transmitter. It was one of the first devices capable of generating the continuous radio waves needed for transmission of amplitude modulation (sound) by radio, and was used for a short period through the 1920s in the first AM radio transmitters, until it was replaced by vacuum tube transmitters. It is on the list of IEEE Milestones as a key achievement in electrical engineering.