Varberg Radio Station
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VLF transmitter Grimeton
|UNESCO World Heritage Site|
|Location||Grimeton, Varberg Municipality, Sweden|
|Criteria||Cultural: (ii), (iv)|
|Inscription||2004 (28th Session)|
Grimeton Radio Station in southern Sweden, close to Varberg in Halland,built in 1922-1924, is an exceptionally well-preserved monument to early wireless transatlantic communication. It was inscribed on the UNESCO World Heritage List in 2004 by following criteria:
- Grimeton Radio Station, Varberg is an outstanding monument representing the process of development of communication technology in the period following the First World War.
- 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.
Grimeton Radio Station was in 2004 inscribed on the UNESCO World Heritage List. The Swedish-American Ernst Alexanderson had developed a technology for wireless telegraphy which came to be used at the radio station in Grimeton. Today, the long-wave transmitter at Grimeton Radio Station, with its alternator and multiple antenna, is unique as the only surviving radio station from the time before radio tubes for high power.
The station in Grimeton, with the callsign SAQ, first started to operate in 1924, mainly for telegraphy with America. The experiences of broken cable connections during the First World War, lead to the decision in the Swedish Parliament in 1921 to build a radio station in Sweden to send morse telegrams across the Atlantic. The premise was to be independent of other countries cable networks. In the 1920s, the industrial race, peace efforts and emigration spurred technological development onward. Bids were requested from Telefunken in Berlin, The Marconi Company in London, Radio Corporation of America (RCA) in New York and Société Francaise Radio-Electrique in Paris. RCA with its high frequency alternator constructed by the Swedish-American Ernst Alexanderson was chosen. After careful calculations, the Swedish station was placed in Grimeton, from where the radio waves were given free passage to the west sea, and over the Atlantic. During the Second World War 1939-1945, the radio station in Grimeton experienced a heyday, when it was Scandinavia’s gateway to the outside world. Cable connections had once again been quickly destroyed by nations at war and the wireless telegraph was a link to the world. Grimeton Radio Station is now the only station left in the once transatlantic network of nine long wave stations that were built during the years 1918-1924, all equipped with the technology that was constructed by Ernst Alexanderson. Alexanderson’s long-wave technology from the 1920s is still fully operational, and is used on special occasions every year using its call sign SAQ.
The principle used is that of a generator (also called alternator) with an exact large number of poles is driven to an exact speed matching the number of pole changes with the desired output frequency (f = poles/2 * revolutions). The switch on and off of the transmitter with the signalling morse key makes the driver motor to change frequency just a bit, so the frequency is outside the narrow band of the antenna and thus transmitted with much less power. In fact this forms an early and clever form of frequency shift keying (FSK). In the days of construction this was the only way known how to output very high power at radio frequencies. Like turning the dynamo of a bike: a dynamo has for instance four poles and by turning this at 100 revolutions (turns) per second the output will be 200 Hertz. If the number of poles in the dynamo are increased to 80 the same driving speed will give us a 4 kHz signal. Increasing both the number of poles and the turning speed makes higher frequencies possible.
Schematic diagram of principle
Between points a and b there will be a signal of 15 (because of 30 poles) times the number of revolutions. The turning rod with electrical windings creating a coil will undergo a sequence of North and South magnetic poles. This induces an alternating current that presents itself on the points a and b. This presented model has fixed (stator) magnets and a rotating (rotor) coil. The places of the two can be exchanged so the magnets are turning in the centre and the coils are in a ring around it. This makes transfer of the coil signal to the next stages (tuning network and antenna) easier.
The antenna system, consisting of high voltage power lines-like antenna towers with antenna wires, has a very low efficiency due to the fact that the length of the antenna is still relative small compared to the output wavelength.
|Wikimedia Commons has media related to Varberg Radio Station.|
- "ERIH Entry: Varberg World Heritage radio station". European Route of Industrial Heritage. 2014. Retrieved 15 January 2015.
- Official website
- World Heritage profile
- SAQ Grimeton at Structurae
- UHF radio and television tower Grimeton at Structurae
- Receive SAQ with soundcard only
- Grimeton VLF transmitter tower 1, SkyscraperPage
- Grimeton VLF transmitter tower 2, SkyscraperPage
- Grimeton VLF transmitter tower 3, SkyscraperPage
- Grimeton VLF transmitter tower 4, SkyscraperPage
- Grimeton VLF transmitter tower 5, SkyscraperPage
- Grimeton VLF transmitter tower 6, SkyscraperPage
- Grimeton TV mast, ScyscraperPage
- Alexanderson Society official webpage (in Swedish)
- Transmission with christmas greetings