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VSAT Introduction
VSAT stands for Ve r y Small Aperture Terminal and refers to receive/transmit terminals installed at dispersed sites connecting to a central hub via satellite using small diameter antenna dishes (0.6 to 3.8 meter). Traditionally, the satellite is a radio relay station that receives, amplifies and redirects analog and digital signals contained within a carrier frequency. These signals contain data, voice, and video communications. VSAT systems can be configured for bi-directional or receive-only operation. In bi-directional operation, the dish both sends (uplinks) and receives (downlinks) the information for use in LANs. What is a Satellite? Any object in the Solar system that revolves around another object that is either static or in motion is a satellite to the latter. For e.g. Earth is a satellite to the Sun & the Moon is a satellite to Earth. How are satellites classified? Broadly we can classify satellites into 2 types: a) Natural Satellites: These are satellites that have been existing even before existence of any living organism on earth e.g. Moon. b) Man made satellites: These are satellites that have been placed into space by human being to achieve a specific purpose. These satellites are sophisticated electronic communications relay station orbiting around the equator moving in a fixed orbit at the same speed & direction of the earth. These satellites like all living things has a specific life time e.g. the INSAT series of satellites which have been launched by India. Why do we need man made satellites? Man made satellite is used in a variety of areas like weather forecasting, communication, navigation systems, television broadcasting etc. What are the different kinds of man made satellite? Based on the orbit in which a satellite is placed we can classify man made satellites as: a) LEO LEO stands for Low Earth Orbit satellite. These satellites circle the earth at a distance that varies from 100 to 300 miles. The orbit in which these satellites are placed is called Polar Orbits. Leo's are also known as Polar Orbit satellites, a Polar Orbit satellite travels from North-South direction. Since these satellites are very close to Earth and to avoid getting pulled back into the gravitational pull of the earth, they have to travel at speeds of 29,359 Kms/ hour and they circle the earth once in every


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90 minutes. Hence they have a rather short life span, as the amount of fuel it uses to stay into orbit is very high. Polar Orbit satellites are mostly used for scanning the Earth's surface. Some of the most

popular areas where Polar Obits satellites are used are Weather Satellite & Remote Sensing satellites. Iridium is another example of LEO satellites. LEO Satellites are deployed for Mobile / Satellite Telephony applications. Good example is Iridium and ICO Global kind of networks.

b) MEO MEO stands for Medium Earth Orbit satellite. These satellites circle the earth at a distance that varies between 6,000 to 12,000 miles and would take approximately 5 to 12 hours to circle the earth once. MEO's are most popular in GPS services.

c) GEO GEO stands for Geosyncronous Equatorial Orbit satellite. These satellites circle the earth at a distance of 22,282 miles or 36,000 Kms. These satellites move at the pace of the earth & will rotate at the same speed, as the earth. As the move at the same speed of the Earth they appear to be stationary. A Satellite placed in the GEO Orbit will take about 24 hrs to complete one rotation. These satellites rotate in an equatorial orbit. Since GEO's move along with the earth's rotation they will cover the same area


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all their life. INSAT 2B and 2C are some examples of Geosynchronous satellites. It takes about 3 satellite placed in the Geosyncronous Orbit to completely cover Earth.

What is an orbit? The path, which a satellite takes to circle round its...
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