English: The tuned circuit of a powerful spark-gap radio transmitter in Australia, during the pioneering days of radio in the second decade of the 20th century. From a 1921 book on radio. The source does not identify the radio station. This was a wireless telegraphy transmitter, that transmitted information by Morse code, not audio as modern radio stations do. The narrow vertical glass jars in the background are Leyden jar capacitors. The two cylinders suspended from the ceiling are the inductively-coupled transmitting coils (inductors) attached to the antenna (not shown). The six small horizontal segmented cylinders mounted in front are quenched spark gaps. The capacitor bank is charged to a high voltage (as much as 75,000 V), until a spark between the segments of the spark gap discharges the capacitors rapidly through the coil, creating radio frequency oscillating currents, which are radiated by the antenna as radio waves.