Description
Unlike the spark-gap transmitter converter, the arc converter produces undamped or continuous waves (CW). This was an important feature as the use of damped waves resulted in lower transmitter efficiency and communications effectiveness, while covering the RF spectrum with interference. This more refined method for generating continuous-wave radio signals was initially developed by Danish inventor Valdemar Poulsen. The Poulsen arc converter can be likened to a continuous-duty-rated electric arc welder with a tuned circuit connected across the arc. The negative resistance characteristics of an electric arc permits the creation of a relaxation oscillator that converts direct current to radio frequency energy. The arc converter consisted of a water-cooled bronze chamber in which the arc burned in hydrogen gas between a carbon cathode and a water-cooled copper anode. Above and below this chamber there were two series field coils surrounding and energizing the two poles of the magnetic circuit. These poles projected into the chamber, one on each side of the arc to provide a magnetic field. This field helps to stabilize the arc and improve overall conversion efficiency. In today's world one can still find oscillators based on negative resistance devices; the tunnel diode is one of them.
It was most successful when made to operate in the frequency range of a few kilohertz to a few tens of kilohertz. The passive frequency multiplier was relied upon to bring the output frequency up to practical transmission frequencies. The frequency multiplier and antenna tuning had to be selective enough to suppress the high harmonic output of the arc converter.
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