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Concept
VSAT
Résumé
A very-small-aperture terminal (VSAT) is a two-way satellite ground station with a dish antenna that is smaller than 3.8 meters. The majority of VSAT antennas range from 75 cm to 1.2 m. Bit rates, in most cases, range from 4 kbit/s up to 16 Mbit/s. VSATs access satellites in geosynchronous orbit or geostationary orbit to relay data from small remote Earth stations (terminals) to other terminals (in mesh topology) or master Earth station "hubs" (in star topology).
VSATs are used to transmit narrowband data (e.g., point-of-sale transactions using credit cards, polling or RFID data, or SCADA), or broadband data (for the provision of satellite Internet access to remote locations, VoIP or video). VSATs are also used for transportable, on-the-move (utilising phased array antennas) or mobile maritime communications.
The concept of the geostationary orbit was originated by Russian theorist Konstantin Tsiolkovsky, who wrote articles on space travel around the beginning of the 20th century. In the 1920s, Hermann Oberth and Herman Potocnik, also known as Herman Noordung, described an orbit at an altitude of whose period exactly matched the Earth's rotational period, making it appear to hover over a fixed point on the Earth's equator.
Arthur C. Clarke's October 1945 Wireless World article (called "Extra-Terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?") discussed the necessary orbital characteristics for a geostationary orbit and the frequencies and power needed for communication.
Live satellite communication was developed in the 1960s by NASA, which launched Syncom 1–3 satellites. Syncom 3 transmitted live coverage of the 1964 Olympics in Japan to viewers in the United States and Europe. On April 6, 1965, the first commercial satellite was launched into space, Intelsat I, nicknamed Early Bird.
The first commercial VSATs were C band (6 GHz) receive-only systems by Equatorial Communications using spread spectrum technology. More than 30,000 60 cm antenna systems were sold in the early 1980s.
Source officielle
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