How it began
Valdemar Poulsen, a Danish engineer, invented an arc converter as a generator of continuous-wave radio signals. The IEEE milestone dates it to 1902, and Britannica and Wikipedia to 1903, the year he obtained an English patent for adapting the "singing arc" to radio. From 1904 he used the arc for experimental transmissions from Lyngby to receiving sites in Denmark and Great Britain.
Before it existed
In the early days of wireless, messages were sent as dots and dashes by spark transmitters, which produced damped waves. Carrying voice or music needed a continuous wave. The English engineer William Duddell had shown in 1900 how to make a resonant circuit with a carbon arc lamp, but his "musical arc" worked only at audio frequencies.
How it works
The device uses an electric arc to turn direct current into radio-frequency alternating current, with a tuned circuit connected across the arc. Poulsen made the arc oscillate at radio frequencies by changing the electrodes to a carbon cathode and a water-cooled copper anode, burning the arc in hydrogen or hydrocarbon vapor, and adding a transverse magnetic field.
How it spread
A syndicate formed in Copenhagen in 1903. Rights were acquired in Britain in 1906 and by C. Lorenz AG in Germany in 1907. In 1909 Cyril Elwell formed the Poulsen Wireless Telephone and Telegraph Company in California, which became the Federal Telegraph Company and built a chain of stations. The US Navy ordered a 100 kilowatt arc in 1913.
What lasted
By 1922 the US Bureau of Standards stated that the arc was the most widely used transmitter for high-power, long-distance work. It was used worldwide until the 1920s, when vacuum tube transmitters displaced it. Britannica credits work with the Poulsen arc with making long-wave radio broadcasting possible by 1920. The IEEE dedicated a milestone plaque at Radio Lyngby in May 1994.
