English: A Bethenod-Latour alternator, a specialized rotating machine that generates radio frequency current, invented during World War 1 by Marius Latour and Joseph Bethenod, which and was used as a high power longwave radio transmitter. It consists of 3 alternators in series, turned by a powerful electric motor. This version produced 225 kW at a frequency of 20 kHz. In order to produce alternating current with high enough frequency for a radio transmitter the alternator had to have many poles and rotate very fast. The advantage of the Bethenod-Latour design was that by combining 3 alternators in series it could produce power at a frequency of 3 times that of each individual alternator, allowing the alternators to rotate slower. Alternator transmitters like this were used from about 1910 to 1930 in superpower transoceanic wireless telegraphy radio stations that exchanged telegraph messages in Morse code with similar stations all over the world.