English: Inductively coupled spark gap radio transmitter circuit patented by German physicist Karl Ferdinand Braun 3 November 1899. The spark gap transmitter was the first type of radio transmitter. The important feature was that this was one of the first inductively coupled (two circuit) transmitters. The Ruhmkorff coil and spark gap (R), Leyden jar capacitors (a) created an oscillating radio current in the primary winding of the transformer (p), which induced current in the secondary winding (s) which was radiated by the antenna (vertical arrow). The inductively coupled or "two circuit" spark transmitter was the first practical type of transmitter; the first that could transmit long distances without interfering with other transmitters, and it was the dominant type used throughout the "spark era" until 1920. Braun shared the 1909 Nobel Prize in physics with Guglielmo Marconi for this invention.