Varberg Radio Station

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Varberg Radio Station
UNESCO World Heritage Site
Varberg Radio Station.jpg
VLF transmitter Grimeton
Official name Grimeton Radio Station, Varberg
Location Grimeton, Varberg Municipality, Halland County, Sweden
Criteria Cultural: (ii), (iv)
Reference 1134
Inscription 2004 (28th Session)
Area 109.09 ha (0.4212 sq mi)
Buffer zone 3,854 ha (14.88 sq mi)
Website The Alexander association
Coordinates 57°6′50.4″N 12°24′15.8″E / 57.114000°N 12.404389°E / 57.114000; 12.404389Coordinates: 57°6′50.4″N 12°24′15.8″E / 57.114000°N 12.404389°E / 57.114000; 12.404389
Varberg Radio Station is located in Sweden
Varberg Radio Station
Location of Varberg Radio Station in Sweden.
Alexanderson alternator in the Grimeton VLF transmitter. The drive motor is at the extreme right; the speed-increaser gearbox is just to its left. Note the bronze-colored shaft coupling.

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.

The radiostation is also an anchor site for the European Route of Industrial Heritage.[1]

A history[edit]

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 Française 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, such as Alexanderson Day.

Working principle[edit]

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[edit]

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.

Principle of a multipole generator for creating radio frequencies.

Antenna system[edit]

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.

Technical Details[edit]

The frequency of operation is 17,200Hz and so the wavelength is approximately 17,442 m. Even though the antenna is approximately 2km long, it is short compared with the wavelength and so it is not very efficient. The six antenna masts each have a 46m cross-arm at the top and are 127m high. Today they carry 8 antenna conductors although originally there were 12. The site was chosen because there is an unobstructed line of sight to New York and a large area of North America.

There are 64 windings on the stator of the alternator/generator, and each provides 100V at up to 30A, i.e. approximately 3kW. Thus the peak RF output power is approximately 64 x 3 kW or 200 kW, although these days it is usually limited to about 80kW. The rotor is a steel disc measuring 1.6m in diameter and approximately 7.5cm thick at the periphery. Around its circumference it has 488 brass filled slots. The air gap between the stator and rotor is 1 mm or less. The motor to drive the generator is capable of delivering 500HP (approximately 370 kW). It is supplied by a 2,200V supply from a transformer-derived 2 phase supply, and turns at 711.3 rpm to obtain the specified frequency of operation. The complete transmitter set weighs about 50 tons. Further details can be found here.

Gallery[edit]

See also[edit]

References[edit]

  1. ^ "ERIH Entry: Varberg World Heritage radio station". European Route of Industrial Heritage. 2014. Retrieved 15 January 2015. 

External links[edit]