Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Communications satellite
open-in-new
<p>A communications satellite is an <a href="/facts/Artificial_satellite/PTX8c68t">artificial satellite</a> that relays and amplifies <a href="/facts/Radio/XFr909M2">radio</a> telecommunication signals via a <a href="/facts/Transponder_(satellite_communications)/rsaCNccw">transponder</a>; it creates a <a href="/facts/Communication_channel/MtlxEShV">communication channel</a> between a source <a href="/facts/Transmitter/nFYghtKv">transmitter</a> and a <a href="/facts/Radio_receiver/5olDTxkg">receiver</a> at different locations on <a href="/facts/Earth/HLLmDfj0">Earth</a>. Communications satellites are used for <a href="/facts/Television/X4YG5nT1">television</a>, <a href="/facts/Telephone/P7uEgWQX">telephone</a>, <a href="/facts/Radio/XFr909M2">radio</a>, <a href="/facts/Internet/Xw1rVvJU">internet</a>, and <a href="/facts/Military/kgNmLUnN">military</a> applications. Many communications satellites are in <a href="/facts/Geostationary_orbit/VBq1v5Kr">geostationary orbit</a> 22,236 miles (35,785 km) above the <a href="/facts/Equator/CjaxbVaN">equator</a>, so that the satellite appears stationary at the same point in the sky; therefore the <a href="/facts/Satellite_dish/4MgSzKnC">satellite dish</a> antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form <a href="/facts/Satellite_constellation/mbTpGjbg">satellite constellations</a> in <a href="/facts/Low_Earth_orbit/rq1TwayJ">low Earth orbit</a>, where antennas on the ground have to follow the position of the satellites and switch between satellites frequently. </p><p>The <a href="/facts/Radio_wave/XmB6WPpF">radio waves</a> used for telecommunications links travel by <a href="/facts/Line-of-sight_propagation/w4xfQd2o">line of sight</a> and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points. Communications satellites use a wide range of radio and <a href="/facts/Microwave/HmVSN31Y">microwave</a> <a href="/facts/Frequencies/QUSbPaW8">frequencies</a>. To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference. </p>