A Satellite phone is also called by various names like satellite telephone or satphone. It is a telephone that transmits and receives from satellites that provide coverage around the world. It is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions. Iridium was the first satellite phone company.
Satphones use Low Earth Orbiting satellites. When a sat phone is switched on, a signal goes up to any number of satellites of a group the phone is registered with. When a person makes a call from the phone, a signal goes to the nearest orbiting satellite. The satellite connects to the gateway or ground station. Then the gateway takes the call to the destination.
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More recent satellite phones are similar in size to a regular mobile phone while some prototype satellite phones have no distinguishable difference from an ordinary smart phone. Satphones are popular on expeditions into remote areas where terrestrial cellular service is unavailable. These phones have connectors for external antennas that are often installed in vehicles and buildings. Some systems also allow for the use of repeaters, much like terrestrial mobile phone systems. Their signals will usually bypass local telecoms systems, hindering censorship and wiretapping attempts.
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Some satellite phones use satellites in geosynchronous orbit, which are meant to remain in a fixed position in the sky at all times. These systems can maintain near-continuous global coverage with only three or four satellites, reducing the launch costs. However the satellites used for these systems are very heavy (approx. 5000 kg) and therefore very expensive to build and launch.
Another disadvantage of geostationary satellite systems is that in many areasâ€â€even where a large amount of open sky is presentâ€â€the line-of-sight between the phone and the satellite is broken by obstacles such as steep hills and forest. The user will need to find an area with line-of-sight before being able to use the phone.
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