English: Spark-gap radio transmitter circuit used by Guglielmo Marconi in his experiments with radio transmission around 1895. It consists of an induction coil B which causes sparks to jump across a spark gap E, creating oscillating electric currents in the wire monopole antenna which are radiated as radio waves. The vibrating interrupter contact on the coil V broke the primary current from the battery B 30-50 times per second, creating the high voltage output from the coil. The radio operator used the telegraph key M to turn the power to the transmitter on and off rapidly, producing different length pulses of radio waves, to spell out text messages in Morse code. The hot-wire ammeter G measured the RF power radiated; when not in use the switch was closed to cut it out of the circuit. Marconi experimented with early radio links at the Villa in Italy Griffone wireless telegraphy Salvan (Valais) in the Swiss Alps in the summer of 1895.