Sainte-Assise transmitter
{{Short description|Radio transmitter in France}}
File:A6.Émetteur de Sainte-Assise.crop.jpg]]
The Sainte-Assise transmitter ({{langx|fr|Émetteur de Sainte-Assise}}) is a very low frequency (VLF) radio transmitter and military installation located on the grounds of the {{interlanguage link|Château de Sainte-Assise|fr}} in the communes of Seine-Port, Boissise-la-Bertrand, and Cesson in the Seine-et-Marne department of the Île-de-France region of France. The transmitter's original equipment was inaugurated on 9 January 1921, at the time being the most powerful radio transmitter on Earth. On 26 November 1921 the first French radio program was transmitted from Sainte-Assise. In 1965 the transmitter was used to send VLF signals to FR-1, the first French satellite. Since 1998 the French Navy has used the transmitter to communicate with submerged submarines.
Design
File:Large spiral inductors in radio transmitter - France 1922.jpgs used for the transmitter in 1922]]
The original equipment of the Saint-Assise transmitter included large spiral "pancake" inductors in a high-power longwave{{cite web |last1=Janberg |first1=Nicolas |title=Sainte-Assise Transmission Masts |url=https://structurae.net/en/structures/sainte-assise-transmission-masts |website=Structurae |access-date=31 August 2021 |language=en, fr, de |date=1998–2021}} alternator transmitter which served as a transatlantic wireless telegraphy station.{{cite journal |title=The New French Radio Central |journal=The Wireless Age |date=October 1922 |volume=10 |issue=1 |page=57 |url=https://books.google.com/books?id=vd7mAAAAMAAJ&pg=PA57 |access-date=31 August 2021}} These combinations of inductors and alternator transmitters were called "oscillation transformers." The primary coil was connected to a large rotating radio frequency alternator which produced the radio signal. The secondary coil was connected to the overhead wire aerial system, over {{convert|1|mi|km}} long, supported on sixteen {{convert|850|ft|m|adj=on}} high towers, which radiated the radio waves. The inductance of the secondary coil resonated with the capacitance of the antenna to form the tank circuit of the transmitter in order to control the output frequency. It transmitted on a wavelength of {{convert|14,300|m|ft}}, or 21 kHz. The station had two 500 kW Alexanderson alternator transmitters and two 250 kW alternator transmitters. The station's transmitters were designed to handle telegram traffic at a rate of 100 words per minute, and all six of them had a combined capacity of 36,000 words per hour.
The spiral shape of the coils reduced resistive losses at radio frequency due to proximity effect. The copper conductors are made in the form of wide strips to increase their surface area in order to reduce their resistance at radio frequencies, since radio frequency currents flow along the surface of conductors due to skin effect.
History
The {{interlanguage link|Compagnie Radio France|fr}}, a subsidiary of Compagnie générale de la télégraphie sans fil (CSF), built the Saint-Assise transmitter.{{cite journal |last1=Griset |first1=Pascal |title=La Société Radio-France dans l'entre-deux-guerres |journal=Histoire, économie & société |date=1983 |volume=2 |issue=1 |pages=83–110 |doi=10.3406/hes.1983.1317 |url=https://www.persee.fr/doc/hes_0752-5702_1983_num_2_1_1317 |access-date=31 August 2021 |language=fr}} The first antenna at Saint-Assise was supported by eleven {{convert|250|m|ft|adj=on}} pylons and five {{convert|180|m|ft|adj=on}} masts. When it opened on 9 January 1921, the transmitter was the most powerful on Earth, capable of broadcasting to the entire planet.{{cite web|url=https://archives.seine-et-marne.fr/seine-port-et-l-emetteur-de-saint-assise|title=Seine-Port et l'émetteur de Saint-Assise|website=archives.seine-et-marne.fr|access-date=31 December 2020|archive-date=23 March 2020|archive-url=https://web.archive.org/web/20200323151610/https://archives.seine-et-marne.fr/seine-port-et-l-emetteur-de-saint-assise|url-status=dead |language=fr}}
On 26 November 1921 the first experimental French radio program was transmitted from Sainte-Assise using a 1 kW-long wave transmitter. As part of the broadcast, opera singer Yvonne Brothier performed La Marseillaise, a song from Mireille, and an aria from The Barber of Seville.{{cite web |last1=Simeon |first1=Michel |title=La Radio a Lyon |url=http://pascalsimeon.free.fr/radioly.htm |website=T.S.F. et Radiodiffusion |access-date=31 August 2021 |language=fr}} Subsequently, the site was a center of early French experiments with television.
In 1941, during World War II, the Kriegsmarine requisitioned Sainte-Assise to allow communications between Berlin and U-boats.{{cite book |last1=Kahn |first1=David |title=Seizing the Enigma: The Race to Break the German U-Boat Codes, 1939–1945 |date=2012 |publisher=Naval Institute Press |location=Annapolis, MD |isbn=978-1591148074 |page=229 |edition=Revised}} Despite this, Sainte-Assise was not targeted or damaged by Allied bombing and all of the antennas survived the war.
The Saint-Assise transmitter played a key role in the 1965 launch of FR-1, the first French satellite. FR-1's mission objective was to study the composition and structure of the ionosphere, plasmasphere, and magnetosphere by measuring the propagation of VLF waves and the local electron density of plasma in those atmospheric layers.{{cite web|url=https://history.nasa.gov/AAchronologies/1965.pdf|title=Aeronautics and Astronautics, 1965|publisher=NASA|page=540|access-date=30 November 2020}}{{cite journal |last1=Ducrocq |first1=Albert |title=La course aux deux infinis |journal=Air & Cosmos |date=25 March 1963 |volume=1 |page=10 |language=fr |issn=1240-3113}}{{cite web |title=FR 1:VLF Receiver |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1965-101A-01 |publisher=NASA Space Science Data Coordinated Archive |access-date=30 November 2020}} For the VLF wave experiments, the Sainte-Assise transmitter and another ground station in Balboa, Panama, transmitted signals at 16.8 kHz and 24 kHz, respectively, while the satellite's magnetic and electric sensors orbiting about {{convert|750|km}} away analyzed the magnetic field of the received wave.{{cite journal |last1=Aubry |first1=M. P. |title=Some results of the FR-1 satellite experiment on the VLF wave field in the zone close to the transmitter |journal=Journal of Atmospheric and Terrestrial Physics |date=1968 |volume=30 |issue=6 |pages=1161–1182 |doi=10.1016/S0021-9169(68)80005-4|bibcode=1968JATP...30.1161A }}
In 1991 part of the station was sold by France Télécom to the French Navy, to become the Sainte-Assise Marine Communications Center ({{langx|fr|Centre de transmissions marine}}; CTM). The CTM, inaugurated in 1998, is tasked with communicating with submerged submarines. An entire company of Fusiliers marins patrols the grounds.
In December 2000 three unused 180-meter pylons were dismantled.
Globecast, an Orange S.A. subsidiary, owns and operates the Sainte-Assise teleport (located on a second site near the Saint-Assise transmitter) which supports multiple parabolic satellite dishes measuring between {{convert|4|m}} and {{convert|16|m}} in diameter. This station ensures the transmission of up-link signals to communications satellites, in particular video and audio signals for the direct broadcasting of satellite radio and television.
See also
References
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{{Coord|48|32|41.10|N|2|34|34.10|E|display=title}}
{{DEFAULTSORT:Sainte-Assise transmitter}}
Category:Towers completed in 1921
Category:Radio masts and towers in Europe
Category:Transmitter sites in France
Category:Buildings and structures in Île-de-France