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 (1.2 mile) 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.
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.
Recent transmissions from SAQ on 17.2 kHz took place on December 24, 2013, June 29, 2014, and December 24, 2014. 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. Next scheduled transmission will be on Alexanderson Day, June 28, 2015, with a CW message being sent at 12:00 UTC. Start-up of the alternator and tests will begin at 11:30 UTC.