The Varberg Radio Station at Grimeton is a VLF transmission facility at Grimeton close to Varberg, in Halland, Sweden. It has the only working Alexanderson alternator rotating armature radio transmitter in the world and is classified as a World Heritage Site. It is an anchor site for the European Route of Industrial Heritage.
The transmitter was built in 1922 to 1924, to operate at 17.2 kHz, although it is designed to operate on frequencies up to 40 kHz. The antenna is a 1.9 km flattop wire aerial consisting of eight horizontal wires suspended on six 127-metre high freestanding steel pylons in a line, that function as a capacitive top-load to feed energy to six grounded vertical wire radiating elements.
The Grimeton VLF transmitter location is also used for shortwave transmissions, FM and TV broadcasting. For this purpose, a 260 metre high guyed steel framework mast was built in 1966 next to the building containing the 40 kHz transmitter.
Until the 1950s, the Grimeton VLF transmitter was used for transatlantic radio telegraphy to Radio Central in Long Island, New York, USA. From the 1960s until 1996 it transmitted orders to submarines in the Swedish Navy.
In 1968 a second transmitter was installed which uses the same aerial as the machine transmitter but with transistor and tube technology. The Alexanderson transmitter became obsolete in 1996 and went out of service. However, because it was still in good condition it was declared a national monument and can be visited during the summer.
On July 2, 2004, the Grimeton VLF transmitter was declared a World Cultural Heritage site by UNESCO. It continues to be used on special occasions such as Alexanderson Day to transmit Morse messages on 17.2 kHz. Its call sign is SAQ. The Grimeton/Varberg site is still used by the Swedish Navy, transmitting on 40.4 kHz using call sign SRC using the vacuum tube transmitter. Since the naval transmitter uses the same aerial as the Alexanderson mechanical transmitter, a simultaneous operation of both transmitters, which would require an expensive high power diplexer, is not possible. Therefore the special transmissions from that machine transmitter are very rare.
At least two regular transmissions take place each year, on the first Sunday of July and on Christmas Eve (24 December), plus one or two extra transmissions on special occasions or for testing.