Goldschmidt alternator

The Goldschmidt alternator or reflector alternator, invented in 1908 by German engineer Rudolph Goldschmidt, was a rotating machine which generated radio frequency alternating current and was used as a radio transmitter. Radio alternators like the Goldschmidt were some of the first continuous wave radio transmitters. Like the similar Alexanderson alternator, it was used briefly around World War I in a few high power longwave radio stations to transmit transoceanic radiotelegraphy traffic, until the 1920s when it was made obsolete by vacuum tube transmitters.

Although the device was a radio transmitter, it resembled an electric generator used to produce electric power in a power plant. Like other generators it consisted of a rotor, several feet in diameter, wound with coils of wire, which rotated inside a stationary frame called a stator which had its own coils. The interaction between the magnetic fields of the rotor and stator produced radio frequency currents in the stator windings, which were applied to the antenna.

A radio frequency alternator differed from an ordinary electric generator in that to produce radio frequency current it rotated much faster, and had many more magnetic "poles" on the rotor and stator, usually 300 to 600. The Goldschmidt alternator was turned by a powerful DC electric motor attached to the shaft, through a geartrain which increased the motor's speed to several thousand RPM. The advantage of the Goldschmidt design was that by using external "reflector" capacitor banks that increased the frequency of the current to a multiple (harmonic) of the alternator's rotation speed, it allowed the rotation speed to be kept lower, simplifying the mechanical design. Goldschmidt transmitters operated at longwave (LF and VLF) frequencies of about 20 to 100 kHz.

...
Wikipedia