10-04-2017, 08:37 PM
SATELLITE COMMUNICATION
INTRODUCTION
Telecommunication systems have made
it possible to communicate with virtually anyone
at anytime. Early Telegraph & telephone systems used copper wire to carry the signal over Earth s
surface & across oceans. High frequency radio also commonly used called shortwave radio.
Historical Background:
First Communication from an artificial earth satellite took place in October 1957 ,it was Soviet satellite SPUTNIK I, for 21 days.
Followed by U.S s Explorer I, in the year 1958 for 5 months for purpose of telemetry.
WHAT IS SATELLITE?
An object in a specific orbit is called a satellite.
A satellite can be natural, like the moon , or human made satellite can travel around planets or around stars such as sun.
Almost every ship launched from earth can be considered as satellite as it is orbiting either the earth or sun.
MODE OF OPERATION:
Normally the satellite is launched at particular orbit .The circular orbit is the most basic orbit and expressed by polar co-ordinates (r, ).
The movement of satellite is affected by the gravitational pull of Sun and Moon.
BASIC CONCEPT OF SATELLITE COMMUNICATION
In satellite communication various components are connected in earth station and satellite.
The main components are transmitting antenna , receiving antenna , transponder etc.
Satellite rotates around a path known as orbits such as geostationary orbit , inclined orbit , low earth orbit etc.
ORBIT OF SATELLITE
Orbit is a path in which satellite rotates around an object.
The life time of satellite is also depends upon orbit , the higher above the earth the orbit, the life time of satellite is longer.
If the orbit is low, the lifetime of satellite is smaller.
UPLINK AND DOWNLINK FREQUENCIES
The frequency of signal from transmitting station to the satellite is called the Uplink Frequency.
The frequency of signal from the satellite to the receiving station is called the Downlink Frequency.
For satellite communication
Uplink Frequency(6GHZ)>Downlink Frequency(4GHz)
TRANSPONDER
The path of each channel from receive antenna to transmit antenna is called a Transponder.
A communication satellite may be considered as a distant repeater whose function is to receive uplink carrier, process them and retransmit the into on the downlink.
Repeater contains the content like filter, amplifier, frequency translator, switches, multiplexer and hybrid.
LAUNCH VEHICLE
Launch vehicle is generally used for launching satellite in a particular orbit.
Four types of satellite launching vehicle is their such as SLV,ASLV,GSLV AND PSLV.
They have different height such as 22m,24m,49m and PSLV is 42.2m. Payload also different.
SLV has 1,ASLV has 2, GSLV has 3 and PSLV has 4 launching stages.
BASICS: FACTORS IN SATELLITE COMMUNICATION
Elevation Angle:
The angle of the horizontal of the earth surface to the center line of the satellite transmission beam.
Azimuth angle:
Because of earth station ,the center of earth, the satellite and sub satellite point all lie in the same plane. the azimuth angle AZ from the earth station to the satellite is same as the azimuth from the earth station to sub satellite point.
Geostationary Earth Orbit(GEO)
These satellites are in orbit 35,863 km above the earth s surface along the equator.
Launching satellite in particular orbit.