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Some satellite phones use satellites in geostationary orbit. These systems can maintain near-continuous global coverage with only three or four satellites, reducing the launch costs. The major satellite systems in civilian use are Inmarsat and Thuraya.
The disadvantage of geostationary satellite systems is that because the satellite is so far away (approx. 22,000 miles), a comparatively large antenna system is required for signal transmission and reception. The physical phone system must therefore be quite large compared to current terrestrial mobile phones. They are similar in size to terrestrial mobile phones of the past.
One serious disadvantage of satellite phones is that the handheld units need a clear view of the sky. Thus they will not work inside buildings, cars or boats. External antennas are required for these uses.
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