English: 100 kW longwave quenched spark gap transmitter at Nauen Radiotelegraphy Station, Nauen, Germany, in 1921. Built by AEG/Telefunken in 1906, this was Germany's most powerful radio station, which provided communication with the outside world during World War 1 when Germany's telegraph cables were cut. This transmitter was built in 1913 but was continuously updated with cutting edge technology. It transmitted on various frequencies between 43 and 100 kHz and had a range of up to 9000 km, sending commercial and diplomatic telegram traffic to Europe, North America and Germany's colonies in Africa by radiotelegraphy, using pulses of radio waves which spelled out text messages in high speed Morse code. The book discusses the components labeled in the picture:

(A) Four relays in the primary circuit of the transformer which keyed the transmitter, operated by a telegraph key in the operations room.
(B) Output porcelain bushings of the supply transformer which supplied 75 to 100 kV to power the transmitter. Most of the huge oil filled transformer is in the room below.
(C) Four glass-topped wooden frames containing quenched spark gaps which discharged the capacitors through the coil. These consisted of a stack of 11 metal disks separated by mica rings, creating 10 narrow spark gaps of 0.1 - 0.4 mm width in series. Blowers in the room below provided air to cool the gaps. Each frame contains 8 quenched gaps each consisting of 10 gaps in series. The transmitter used one frame, while the other frames served as backups or were being serviced.
(D) Oil capacitor bank against back wall, which was connected to the tuning coil to make the tuned circuit of the transmitter. These consisted of iron tanks each containing many parallel metal plates suspended in insulating oil.
(E) Wooden cases containing the tuning coil which formed the tuned circuit with the capacitors, and the variometer loading coil to tune the huge wire antenna to resonance with the transmitter.

A separate power room held a backup steam generator and a motor-alternator set which powered the transformer, changing the 50 Hz power line frequency to 500 Hz, to create a spark rate of 1000 sparks per second, which gave the radio signal a musical tone in receiver headphones which cut through interference well.