The Grimeton VLF transmitter is a VLF transmission facility at Grimeton close to Varberg, Sweden. It has the only working Alexanderson alternator rotating armature radio transmitter in the world and is classified as a World Heritage Site.
The transmitter was built in 1922 to 1924; to operate at 17.2 kHz, although it is designed on frequencies up to 40 kHz. The radiating element is a wire aerial hung on six 127-metre high freestanding steel pylons, that are grounded.
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.
In 1945 the Grimeton VLF transmitter's twin station Nadawcza Radiostacja Transatlantycka Babice in Babice, Poland was destroyed. 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.
A recent transmission from SAQ on 17.2 kHz took place on July 1, 2012 and the next one is scheduled for October 24, 2012. 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.