The multiple-tuned antenna used at Grimeton is a pre-WW1 invention by E F W Alexanderson, which uses a number of vertical radiator wires interconnected by the flat-top wires, which serve both as top capacitance and as a high-voltage transmission line. Each vertical wire is terminated in a ground-mounted tuning inductance (or "coil") which serves to tune out the capacitive reactance of the wire, and to establish the proper phase relationship between the currents in the wires. By dividing the total current flowing into the ground or counterpoise system between several connection points, the equivalent ground loss resistance may be substantially reduced compared to the case when all current is fed into a single vertical radiator. This increases the antenna efficiency with about an order of magnitude. Technical details To achieve maximum range, like other transoceanic radiotelegraphy stations of this era it transmitted in the VLF band, at a frequency of 17.2 kilohertz and so the wavelength is approximately 17,442 meters. Even though the antenna is approximately 2 km long, it is short compared with the wavelength and so it is not very efficient. The six antenna masts each have a 46m cross-arm at the top and are 127m high. Today they carry 8 antenna conductors although originally there were 12. There are 64 windings on the stator of the alternator/generator, and each provides 100 V at up to 30 A, i.e. approximately 3 kW. Thus the peak RF output power is approximately 64 x 3 kW or 200 kW, although these days it is usually limited to about 80 kW. The rotor is a steel disc measuring 1.6 m in diameter and approximately 7.5 cm thick at the periphery. Around its circumference it has 488 brass filled slots. The air gap between the stator and rotor is 1 mm or less. The motor to drive the generator is capable of delivering 500 HP (approximately 370 kW). It is supplied by a 2,200V supply from a transformer-derived 2 phase supply, and turns at 711.3 rpm to obtain the specified frequency of operation. The complete transmitter set weighs about 50 tons. Further details can be found here. Gallery See also List of masts List of towers References External links Official website World Heritage profile Explore Grimeton Radio Station in the UNESCO collection on Google Arts and Culture Alexander - Grimeton Veteran Radio's Friends Receive SAQ with soundcard only Grimeton VLF transmitter tower