Editing Motor–generator (section)

==High-frequency machines==
An [[Alexanderson alternator]] is a motor-driven, high-frequency alternator which provides [[radio frequency]] power. In the early days of radio communication, the high frequency [[carrier wave]] had to be produced mechanically using an [[alternator]] with many poles driven at high speeds. Alexanderson alternators produced RF up to 600&nbsp;kHz, with large units capable of 500&nbsp;kW power output. While electromechanical converters were regularly used for [[long wave]] transmissions in the first three decades of the 20th century, electronic techniques were required at higher frequencies. The Alexanderson alternator was largely replaced by the vacuum tube oscillator in the 1920s.