English: One of the earliest vacuum tube radiotelephone transmitters, built by German scientist Alexander Meissner in 1913. In a historic test in June 1913, Meissner used it to transmit voice 36 km (24 mi) from Berlin to Nauen, Germany. It used a mercury vapor triode vacuum tube (large tube visible) developed beginning in 1906 (approximately at the same time as De Forest's Audion tube) by Austrian engineers Robert von Lieben and Eugen Riesz. The large Lieben-Riesz tube (right) was used in the Meissner oscillator transmitter circuit which he had developed earlier that year, while the receiving circuit used a smaller Fleming valve (left). It transmitted on a wavelength of 600 m (500 kHz) with an output power of 12 W with 440 V on the plate, modulated with a carbon microphone in the antenna lead. H. J. Round noted that when the Leiben tube was used at such power levels, the tube lasted only 10 minutes before the filament burned out due to bombardment by mercury ions.