English: Spark gap radio transmitter of long distance wireless telegraphy radio station built by Gesellshaft fur Drahtlose Telegraphie (Telefunken) at Nauen, Germany in 1907. Designed by German radio pioneer Georg von Arco, this was Germany's first high power radio station and (using a more powerful transmitter) served as Germany's main communication channel with other nations during World War 1. The bank of narrow Leyden jar capacitors are visible in the background. The 360 jars have a total capacitance of 400 microfarads. The tuning coil (oscillation transformer), a spiral of silver-plated tubing, which with the capacitors make up the tuned circuit, is partially visible between the banks of jars. On the right are the spark gaps that excite oscillations in the tuned circuit. Four are used in parallel, with two held as spares which can be switched into the circuit if one of the four fails. On the extreme right along the floor are two choke coils which protect the high voltage supply transformer (located in another room) from the oscillating radio frequency current in the tuned circuit. The technician is measuring the output frequency with an absorption wavemeter. Since mains power was not yet available the station was powered by an oil engine turning a 35 horsepower (26 kilowatts) alternator. The transmitter's radiated power was about 10 kW in the very low frequency band using a 300 ft. high wire umbrella antenna, and it could be received at a range of about 3,500 kilometres (2,200 miles).