Grimeton Radio Station () in southern Sweden, close to Varberg in Halland, is an early longwave transatlantic wireless telegraphy station built in 1922–1924, that has been preserved as a historical site.
Beginning in the 1920s, it was used for wireless communications to North America and other countries, and during World War II was one of Sweden's few telecommunication links to the rest of the world. It is home to the only remaining example of an early pre-electronic radio transmitter technology called an Alexanderson alternator. 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."
The radio station is also an anchor site for the European Route of Industrial Heritage. The transmitter is still in operational condition, and each year on a day called Alexanderson Day is started up and transmits brief Morse code test transmissions, which can be received all over Europe.
History
Beginning around 1910 industrial countries built networks of powerful transoceanic longwave radiotelegraphy stations to communicate telegraphically with other countries. During the First World War radio became a strategic technology when it was realized that a nation without long-distance radio capability could be isolated from the rest of the world by an enemy cutting its submarine telegraph cables. Sweden's geographical dependence on other countries' underwater cable networks, and the temporary loss of those vital connections during the war, motivated a decision in 1920 by the Swedish Parliament that the Royal Telegraph Agency build a high-power radiotelegraphy station in Sweden to transmit telegram traffic across the Atlantic.
At the time, there were several different technologies used for high-power radio transmission, each owned by a different giant industrial company. 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. The transmitter chosen was the 200 kW version of the Alexanderson alternator, invented by Swedish-American Ernst Alexanderson, manufactured by General Electric and marketed by their subsidiary RCA. This consisted of a huge rotating electromechanical AC generator (alternator) turned by an electric motor at a fast enough speed that it generated radio frequency alternating current, which was applied to the antenna.
It was one of the first transmitters to generate sinusoidal continuous waves, which could communicate at longer range than the damped waves which were used by the earlier spark gap transmitters. The alternator was chosen because it was already used in most other transatlantic radio stations, reducing potential compatibility problems. The fact that it was designed by a Swede may have also played a part.
After careful calculations, the station was located in Grimeton, on the southwest coast of Sweden nearest North America, which allowed good radio wave propagation conditions over the North Atlantic to America, and also Norway, Denmark, and Scotland. The site was purchased in autumn 1922, construction began by the end of the year, and the station was finished in 1924. Two 200 kilowatt Alexanderson alternators were installed, to allow maintenance to be performed on one without interrupting radio traffic.
To achieve daytime communication over such long distances, transoceanic stations took advantage of an earth-ionosphere waveguide mechanism which required them to transmit at frequencies in the very low frequency (VLF) range below 30 kHz. Radio transmitters required extremely large antennas to radiate these long waves efficiently. The Grimeton station was equipped with a huge multiple-tuned flattop antenna 2.2 km (1.3 miles) long consisting of twelve (later reduced to eight) wires supported on six 127 m (417 foot) high steel towers, fed at one end by vertical feeder wires extending up from the transmitter building. The station started operation on 1 December 1924, transmitting radiotelegraphy traffic with the callsign SAQ on a wavelength of about , later changed to , to RCA's receiving station in Riverhead, New York. It immediately took over 95% of the Swedish telegram traffic to the United States.
The Alexanderson alternator technology was becoming obsolete even as it was installed. Vacuum tube electronic oscillator transmitters, which used the triode vacuum tube invented by Lee De Forest in 1907, replaced most pre-electronic transmitters in the early 1920s. 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 wave transmissions, 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.
During the Second World War 1939–1945, the station experienced a heyday, when it was one of Scandinavia's gateways to the outside world. 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. Several new transmitters were therefore added to the station. 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.
Following the war, additional transmitters were installed and the number of destinations increased, reaching a peak in the 1950s when the station operated twelve shortwave transmitters and one electronic longwave transmitter (as well as the original Alexanderson system), maintaining traffic to some twenty countries in Europe, Asia and the Americas. By that point, the telegraphic transmissions had shifted from Morse code to radioteletype and the station also provided radiofax and radiotelephony services. In the early/mid-1950s, experimental FM and TV transmitter installations were made at the site, using the towers as antenna supports.
By the 1960s, many of the transmitters were beginning to show their age and were subsequently decommissioned, being replaced by more modern equipment. 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 circuits for international communications in favour of satellites and new types of cables. Instead, focus would eventually shift to long-range maritime radio. Also, modern FM and TV transmitters were installed in the new facility, which has a 260 m high antenna support tower.
The system installed in the new facility in two installments during the mid-60s and early-70s consisted of eight 30 kW Telefunken SV2470 HF transmitters and one 100 kW Telefunken HF transmitter, together with one 40 kW Telefunken LF transmitter. All HF transmitters shared a common antenna park, consisting of rhombic, discone and log-periodic antennas. The HF system was designed for international point-to-point telegraph and telephone circuit, but already in the mid-70s they started to fall out of fashion, with the last remaining being the Shanghai, Tokyo and Buenos Aires HF circuits, which were closed in the late-70s and early-80s.
The transmitter set-up was then mostly used as a contingency back-up and for maritime HF services, air-ground radio and for SSB broadcasting trials. In the 1980s, the maritime radiotelex system MARITEX required more capacity, so several smaller HF and MF transmitters were added, sharing the antennas using diplex and triplexer filter networks. For a brief period in the 1990s the experimental aeronautical HF digital datalink (HFDL) system used the station as one of its transmitter sites. All pre-1980s LF and HF transmitters in the new building have since been decommissioned and scrapped.
The early 1990s saw the corporatisation of Televerket, the Swedish telecom agency, with its successor Telia taking ownership of the site, apart from the new station building which was sectioned off and transferred to Teracom.
Preservation
The changed conditions meant that the future of the old radio station became much more uncertain as Telia was expected to streamline its operations. Various scenarios were considered, including the demolition of the six antenna towers. In stark contrast to this stood the potential preservation of the site as a museum and a historical monument, an idea which had been floated within the Swedish telecom agency already in the early 1970s but had not been realised. The extensive and much-needed restoration efforts this solution would require, and the related costs, were initially a source of hesitancy for the newly-formed Telia.
The potential loss of a landmark did however cause a rise in public interest and by the mid-1990s former employees, locals and other interested parties were working together with Telia and the county administrative board of Halland to ensure the radio station's continued existence. With funds received from the Swedish National Heritage Board, restoration could begin while the station's buildings and antenna towers became listed in 1996.
These efforts laid the groundwork for what would eventually result in the site's inscription on the World Heritage List. Based on its authenticity and integrity as a monument to early wireless communications, the decision to include the property was passed at the 28th session of the World Heritage Committee held in Suzhou in 2004.
In 2003, the ownership of the radio station was handed over to a foundation, Stiftelsen Världsarvet Grimeton, tasked with the management of the site. An association of volunteers, Alexander, contributes to the continued maintenance and operation of the Alexanderson transmitter. Having had a long history of being closed to the general public, the old radio station is nowadays open to visitors. To facilitate this purpose, a visitor center was built in 2005 and expanded ahead of the site's centennial celebrations in 2025.
The property remains a source of radio transmissions with the still operational Alexanderson transmitter being used for the transmission of telegrams on certain occasions, such as Alexanderson Day, United Nations Day and Christmas Eve, using its historical frequency of 17.2 kHz as well as its call sign SAQ. The site is also home to the HAM radio station SK6SAQ.
Commercial operations are also ongoing. The year 2000 saw the decommissioning of MARITEX, freeing up a large number of transmitters and antennas, which were then leased to the Globe Wireless system for maritime HF digital communications. When the Globe Wireless operations ceased in 2012, the HF antenna and feed-line system was re-purposed for air-ground voice HF services, following the decommissioning of and moving from their original Karlsborg transmitter site, which claim to be the only remaining civilian commercial user of the facilities. The Swedish Maritime Administration also leases transmitter and antenna spaces for MF telephony and NAVTEX transmitters at the site. Their NAVTEX antenna is of a special design, using one 127 m high tower as a folded monopole antenna, self-resonant on 518 kHz.