This PPT presentation is based on the topic Satellite Communications
Satellite Communications is very common topic for seminar presentation.
This ppt slide on Satellite Communications is a guidline for students or proffesional preparing for seminar presentation on Satellite Communications.
A satellite is something that goes around and around a larger something, like the earth or another planet.
Some satellites are natural, like the moon, which is a natural satellite
of the earth.Other satellites are made by scientists and technologists to go around the earth and do certain jobs.
Some satellites send and receive television signals. The signal is sent from a station onthe earth’s surface.
The satellite receives the signal and rebroadcasts it to other places
on the earth.
To Avoid number of Repeaters on the earth surface.
Avoiding Line of Sight Propagation.
High coverage area i.e. a single satellite covers 48% earth surface. For this we require 3 satellites to cover the total surface.
To avoid obstacles like building, tree, mountain etc.
The satellite, as a repeater.
receives the uplink signals from the earth stations,
translates them to the down link frequency band
amplifies them, and
transmits back to the earth station.
The up-link and down-link signals are modulated carriers as in terrestrial microwave links.
The satellite as repeater, does not distinguish between the type of modulated used in the carrier.
It can be a frequency modulated carrier.
Orbit is a path traversed by a satellite, orbit may be Equilateral, inclined and Polar.
The parameters of the orbit are defined by three laws of Kepler.
Following figure shows the period of revolution of a satellite as a function of its altitude.
If the revolution of satellite around the earth is equal to rotation of the earth along its axis, then the satellite is called Geostationary satellite.
The satellite orbit is placed at a distance of 36000 km from the centre of the earth.
On the other hand, a satellite which appears to be immobile when seen from the earth, is called geostationary.
Majority of the communication satellites are geostationary for the very practical reason that an earth station antenna can be easily pointed towards its.
Transmission path of a communication link through a satellite is about 72000 km long (36000 km uplink path and 36000 km downlink path).
Electromagnetic waves traveling at 3 x 105 km/sec take about 240 ms. from one end to the other.
Such large propagation delay is at the limit of psychologically tolerable values in telephony.
The propagation delay results in “echo” in a telephony channel.
A special equipment called echo suppressors is incorporated in the earth station to counteract the echo.
The equipment carried about a satellite essentially consists of
Payload refers to the equipment used to provide the service for which the satellite has been launched.
In communication satellites, payload consists of transponders which carry out the repeater function and the transmit and receive antennas.
Support subsystems include altitude and orbit control equipment, power subsystem, telemetry and tele-command subsystem, etc.
Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects.
Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation.
are an artificial satellite stationed in space for the purposes of telecommunications.
Modern communications satellites typically use geosynchronous orbits, Molniya orbits or low Earth orbits.
LOW EARTH ORBIT(LEO):
Low Earth Orbit (LEO)) refers to a satellite which orbits the earth at altitudes between (very roughly) 200 miles and 930 miles.
Medium Earth Orbit (MEO):
Medium Earth Orbit (MEO) refers to a satellite which orbits the earth at an altitude below 22,300 miles (geostationary orbit) and above the altitude of Low Earth Orbit (LEO) satellites.
High Earth Orbit (HEO):
Geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,240 miles).
Geosynchronous Orbit (GEO):
In other words, if a satellite in a geostationary orbit is in a certain place above the earth, it will stay in that same spot above the earth.
Geostationary satellites are commonly used for communications and weather-observation
Advantages of Satellite Communications:
Suitable for both Digital and Analog Transmission
Quick Provision of Services
Mobile and Emergency Communication
In India, satellite communication has been in use for overseas communication by Videsh Sanchar Nigam Ltd. for many years.
This service is provided through INTELSAT satellite.
Two locations in the geostationary orbit were reserved for Indian satellites i.e.74o east and 93.5o west.
Series of four satellites (INSAT–I series) was planned .
By going through the above slides we came to know that satellite is mostly responsible for telecommunication transmission and reception of television signals and wheather forcasting which is very important in our daily life. Satellites are having some disadvantages till now.if they are improved to an extent that the delay will be minimized then I will be a golden achievement of science in our life.