English: A Righi spark gap, a type of spark gap invented by Agusto Righi in the 1890s for use in spark gap radio transmitters. This type was used by radio pioneer Guglielmo Marconi in his pioneering experiments in radio communication between 1894 and 1898; Marconi had studied with Prof. Righi. In spark gap radio transmitters, the first type of radio transmitter, used between 1886 and 1916, a high voltage spark between two conductors created radio frequency oscillating currents, which were radiated as radio waves. A spark transmitter's output power depended on the voltage applied to the gap. To reach a higher voltage a wider spark gap had to be used. But at wide gaps the energy lost in the long spark limited the output power.

The Righi gap consisted of 3 spark gaps between 4 metal balls. The 2 outer gaps (visible) served merely to charge the inner metal balls; the gap between the 2 inner balls generated the radio waves. This gap was surrounded by a container filled with an insulating oil or grease. The theory was its presence in the gap allowed a far greater voltage to be applied before the gap arced, without creating a long energy-wasting spark.

Caption: Early Form of Discharger

Alterations to image: Partially removed aliasing artifacts (crosshatched lines) introduced during the scanning of the original halftone photo, using the Gimp FFT filter.