The Alexanderson alternator, a "near perfect" system of W/T transmission

In 1903, Steinmetz built a 1 kW 10 kHz alternator which was used by Fessenden in experiments with wireless telephony, and in 1904 he placed an order with the General Electric Company (USA) to design and build an alternator capable of operating at a frequency of 100 kHz. General Electric handed the order to Alexanderson to design. Alexanderson tested special Swedish iron strips 1.5 mills thick in strong magnetic fields, and found the iron capable of satisfactory operation at 100 kHz, so he designed the alternator with an iron core. However Fessenden rejected the design and insisted on the use of a wooden core as he was sure that iron would melt in a strong magnetic field at 100 kHz. By 1915 a 50 kW, 50 kHz experimental alternator was being tested and Dr. Alexanderson was able to modulate it with voice, using a Deforest Audion valve to control a magnetic amplifier.