English: A Goldschmidt alternator, a rotating machine developed in 1908 by Rudolph Goldschmidt for use as a radio transmitter. This example has an output power of 12.5 kW and efficiency of 80% at a frequency of 30 kHz, and 8 to 10 kW at a frequency of 60 kHz. It was installed 1910 by C. Lorentz Co. at their Eberswald wireless station. It consists of a DC motor (left) which drives the alternator (right) through a geartrain (center). In order to produce high frequencies the alternator rotor and stator have a large number of poles, usually 200 to 400. The unique advantage of the Goldschmidt machine was that its rotor and stator were connected to tuned circuits - "reflector circuits" (capacitor bank visible on back wall) - which caused the machine to produce its output power at a multiple (harmonic) of its rotational rate, so it could produce high frequencies without the high rotational speed that the Alexanderson alternator required.