It was added to the UNESCO World Heritage List in 2004, with the statement: "Grimeton Radio Station, Varberg is an exceptionally well preserved example of a type of telecommunication centre, representing the technological achievements by the early 1920s, as well as documenting the further development over some three decades."

Bids were requested from Telefunken in Berlin, The Marconi Company in London, Radio Corporation of America (RCA) in New York and Société Française Radio-Electrique in Paris.

However the large capital investment in an alternator transmitter caused owners to keep these huge behemoths in use long after they were technologically obsolete.

By the mid-1930s most transatlantic communication had switched to short waves, and, beginning in 1938, vacuum tube shortwave transmitters were installed in the main building, using dipole and rhombic antennas in a neighbouring field.

The Alexanderson alternator found a second use as a naval transmitter to communicate with submarines, as VLF frequencies can penetrate a short distance into seawater.

Underwater communication cable connections had once again been quickly severed by nations at war and the radiotelegraphy transmissions were a link to the outside world.

As users during the war included the Swedish Ministry for Foreign Affairs and various embassies and legations, the radio station’s transmissions were subject to interception by signals intelligence operations such as the British Y service.

By that point, the telegraphic transmissions had shifted from Morse code to radioteletype and the station also provided radiofax and radiotelephony services.

However, rather than refitting the original station building, a new facility was built in 1966 to house the new transmitters, a move which allowed for the preservation of the older equipment.

Several new antennas were also erected in the mid-to-late 1960s, but these investments were relatively short-lived in their original context as they coincided with the move away from using fixed radio stations for international communications in favour of satellites and new types of cables.

The Grimeton transmitter is the last surviving example of an Alexanderson alternator, the only radio station left from the pre-vacuum tube era, and is still in working condition.

Each year, on a day called Alexanderson Day, either on the last Sunday in June, or on the first Sunday in July, whichever comes closer to 2 July, the site holds an open house during which the transmitter is started up and transmits test messages on 17.2 kHz using its call sign SAQ, which can be received all over Europe.

This is set in rotation by a motor (500 HP, 711.3 rpm) via a gearbox (setup ratio: 2.97) and thus generates a continuous sinusoidal AC voltage (B) of 17.2 kHz or 17,200 Hz.

As known from historical radios, the antenna and the adjacent coils and capacitors form an resonant circuit, which must be tuned to the desired frequency so that the energy is optimally transmitted.

The magnetic amplifier is an arrangement of coils and capacitors whose AC resistance is indirectly influenced by the Morse key and a DC source.

In order to achieve the necessary transmission frequency, the generator of the Alexanderson alternator type [8] [9] must not only rotate quickly, but it also needs a special construction with many magnetic poles.

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 17442 meters.