English: Drawing of a quenched spark gap, a type of spark gap invented in 1906 by German physicist Max Wein and used in spark gap radio transmitters until the mid 1920s. It consists of a stack of metal disk electrodes separated by thin mica washers (M) to create multiple microscopic spark gaps (S) between their surfaces. The disks' edges are often extended to make a heat radiating fin (F) which is cooled in use by forced air.

The quenched gap was used in inductively coupled spark transmitters. In the inductively coupled transmitter, a capacitor was discharged by the spark gap through a tuned circuit consisting of the primary winding of an air core transformer to create radio frequency oscillating currents. These induced currents in the secondary winding of the transformer, which was connected to an antenna which radiated the energy as radio waves. When an ordinary spark gap was used, the energy repeatedly passed back and forth between the secondary and primary winding, thus dissipating much of the energy in the spark. The purpose of the quenched gap was to terminate ("quench") the spark after the energy had been transferred to the secondary. The wide metal surfaces of the electrodes cooled and absorbed the ions in the spark when the current in the primary circuit momentarily went to zero after the energy transferred to the secondary. This left the energy in the secondary tuned circuit and antenna to oscillate freely, producing long "ringing" waves. Quenched spark transmitters had lower damping and thus narrower bandwidth than ordinary transmitters, allowing them to both transmit further and radiate less W:radio noise which interfered with other transmitters' signals.