Grimeton Radio Station
UNESCO World Heritage Site | |
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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 |
Grimeton Radio Station (Swedish pronunciation:
History
Beginning around 1910 industrial countries built networks of powerful transoceanic
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
After careful calculations, the station was located in Grimeton, on the southwest coast of Sweden nearest North America, which allowed good
The Alexanderson alternator technology was becoming obsolete even as it was installed.
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. One of the alternator transmitters was scrapped in the 1960s. The alternator continued to be used for naval transmissions until the mid-1990s, when a modern solid-state LF transmitter replaced it.
Grimeton Radio Station is now the only station left in the transatlantic network of nine long wave stations that were built during the years 1918–1924, all equipped with Alexanderson alternators. In 2004 it was added to the UNESCO World Heritage List. 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.
Technical description
The electromechanical transmitter in Grimeton transmitted at a frequency of 17.2 kHz, i.e. in the VLF range, and was thus able to reach America.
In principle, an electric generator (A) is used for this purpose. 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. [6]
For comparison, generators of the public electricity networks produce an alternating voltage of 50 or 60 Hz, depending on the country. To produce such high frequencies with a generator, a fast-rotating generator (2115 revolutions per minute) with a special design is necessary.
In Grimeton, mainly Morse signals were transmitted. To send information with the generated alternating voltage, the texts to be sent are translated into a sequence of short and long pulses according to the Morse code by means of a Morse key (D). The switchgear (C) uses these pulses to control the transmission of the AC voltage to the antenna (F). When the key is pressed, the AC voltage is passed on to the antenna and transmitted from there. If the key is not pressed, the AC voltage is suppressed by the switchgear and no signal is transmitted. Thus, for example, as shown in (E), the letter A can be transmitted by a short and a long wave packet and detected at the receiver.
The AC voltage generated has a voltage of 2000 volts [7] and a power of 200 kW [6] (although these days it is usually limited to about 80 kW). Such strong signals cannot be switched on and off by a simple switch, it would cause considerable sparking. In Grimeton, a different effect was used for this purpose.
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. In Grimeton, the tuning of this oscillating circuit is now disturbed in the switchgear (C) when the Morse key is not pressed, thus suppressing transmission. Thus it is possible to influence an AC power of 200kW with a small power (3 kW DC).
The antenna resonant circuit essentially consists of the antenna (I), a transformer (D) and a magnetic amplifier (G).[6][8]
As usual in electric generators, an alternating voltage is generated in adjacent coils (B) in the generator (A) by means of rotating magnetic fields. In Grimeton, these coils are mounted on the stator, divided into 2x32 sectors, on both sides to the rotor. The individual windings of a sector are connected to corresponding primary windings (C) of the transformer (D). When the primary voltages are transmitted to the secondary winding (E) of the transformer, these voltages are superimposed to form a strong, sinusoidal output signal which is output to the antenna and transmitted.
The control winding (F) and the magnetic amplifier (G) are responsible for controlling the transmission process by the Morse key (H). The magnetic amplifier is an arrangement of coils and capacitors whose AC resistance is indirectly influenced by the Morse key and a DC source. When the Morse key is open, the solenoid amplifier short-circuits the control winding (F), to put it simply. The short-circuiting of (F) disturbs the transmitting oscillating circuit, so that finally no more than 9 % of the normal antenna current flows [2, page 53]. The situation described above (full transmit or no transmit at all) can therefore only be achieved approximately, but this is sufficient in practice.
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. For this purpose, the steel, and thus magnetizable rotor disk (A) is provided at the edge with 488 slots (B), which are filled with a non-magnetic material.[7] By means of the coils (D), a continuous magnetic field (E) is generated in the stator by means of direct current, in which the coils (C) are also located. Due to the rotating rotor disk, this magnetic field between the coils (C) is alternately reinforced by the steel disk and the non-magnetic slots are damped. This cyclically changing magnetic field induces a sinusoidal voltage in the coils (C).
The above sketch is not to scale, the air gap between rotor and stator frame is only 1mm wide.[8] The rotor is a steel disc measuring 1.6 m in diameter and approximately 7.5 cm thick at the periphery.
Antenna system
To achieve maximum range, like other transoceanic radiotelegraphy stations of this era it transmitted in the
The antenna system consists of antenna wires supported by masts, such as those used for high-voltage power lines. 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 multiple-tuned antenna used at Grimeton is a pre-WW1 invention by E F W Alexanderson, which uses a number of vertical radiator wires interconnected by the flat-top wires, which serve both as top capacitance and as a high-voltage transmission line.
Each vertical wire is terminated in a ground-mounted tuning inductance (or "coil") which serves to tune out the capacitive reactance of the wire, and to establish the proper phase relationship between the currents in the wires.
By dividing the total current flowing into the ground or counterpoise system between several connection points, the equivalent ground loss resistance may be substantially reduced compared to the case when all current is fed into a single vertical radiator.
This increases the antenna efficiency with about an order of magnitude.
Gallery
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1900 meter (1.2 mile) flattop antenna
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Interior of Grimeton radio station
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Log-periodic shortwave antenna beside the transmitter building
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Interior of transmitter hall showing control panel for alternator
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Interior of transmitter hall showing Alexanderson alternator
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Grimeton World Heritage entrance hall
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A warning sign at the entrance
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Grimeton VLF masts.
See also
- List of masts
- List of towers
References
- ^ Jöran Sahlgren; Gösta Bergman (1979). Svenska ortnamn med uttalsuppgifter (in Swedish). p. 9.
- ^ "ERIH Entry: Varberg World Heritage radio station". European Route of Industrial Heritage. 2014. Retrieved 15 January 2015.
- ^ a b c d e f g "History". Grimeton Radio Station World Heritage Site. World Heritage Grimeton. Retrieved 22 April 2023.
- ^ a b "A Great Swedish Station". Experimental Wireless & The Wireless Engineer. 2 (16). London: Iliffe & Sons: 224. January 1925. Retrieved 7 February 2023.
- .
- ^ a b c "The Alexanderson transmitter – The Alexander association". Retrieved 2023-10-31.
- ^ a b "CW or MCW? – Föreningen Alexander". Friends of Grimeton Veteran Radio. Retrieved 2023-10-31.
- ^ a b c Bucher, Elmer E. (1920). "Technical description of the Alexanderson system for radio telegraph and radio telephone transmission". HathiTrust. Retrieved 2023-10-31.
- ^ Mayes, Thorn L. "The Alexanderson 200 KW High Frequency Alternator Transmitters" (PDF). Society of Wireless Pioneers -Historical Papers. Retrieved 2023-10-31.
External links
- Official website
- World Heritage profile
- Explore Grimeton Radio Station in the UNESCO collection on Google Arts and Culture
- Alexander - Grimeton Veteran Radio's Friends
- SAQ Grimeton at Structurae
- UHF radio and television tower Grimeton at Structurae
- Receive SAQ with soundcard only Archived 2015-11-21 at the Wayback Machine
- 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