-
8/3/2019 Sati Communication
1/3
What is sati communication?
In satellite communication, signal transferring between the
sender and receiver is done with
the help of satellite. In this process, the signal which is
basically a beam of modulated
microwaves is sent towards the satellite. Then the satellite
amplifies the signal and sent itback to the receivers antenna
present on the earths surface. So, all the signal transferring
is happening in space. Thus this type of communication is known
as space communication.
Two satellites which are commonly used in satellite
communication are Active and
passivesatellites.
Passive satellites: It is just a plastic balloon having a metal
coated over it. This sphere
reflects the coming microwave signals coming from one part of
the earth to other part. This
is also known as passive sphere. Our earth also has a passive
satellite i.e. moon.
Active satellites: It basically does the work of amplifying the
microwave signals coming. In
active satellites an antenna system, transmitter, power supply
and a receiver is used.
Thesesatellites are also called as transponders. The
transmitters fitted on the earth
generate the microwaves. These rays are received by the
transponders attached to the
satellite. Then after amplifying, these signals are transmitted
back to earth. This sending
can be done at the same time or after some delay. These
amplified signals are stored in the
memory of the satellites, when earth properly faces the
satellite. Then the satellite starts
sending the signals to earth. Some active satellites also have
programming and recording
features. Then these recording can be easily played and watched.
The first
active satellite was launched by Russia in 1957.The signals
coming from the satellite when
reach the earth, are of very low intensity. Their amplification
is done by the receivers
themselves. After amplification these become available for
further use.
-
8/3/2019 Sati Communication
2/3
Microwave communication is possible only if the position of
satellite becomes stationary
with respect to the position of earth. So, these types of
satellites are known
as geostationarysatellites.
What are the requirements for a satellite to be
geostationary?
1. Its revolutionary direction must be same as that of the
earth, i.e. from west to east.
2. The time period of satellites revolution must be same to the
time period of the rotation of
earth along its polar axis, which is equal to 24 hours.
3. The equatorial plane of earth must be coplanar with the
orbital plane of
the satellitesrevolution.
The name given to the orbit of the geo-stationary satellites is
synchronous orbit. Due to this
geo-stationary satellites are also called as geo-synchronous
satellites. Geo-
synchronous orbit is at a height of nearly 36000km from the
surface of earth.
These orbits are capable of giving a successful communication
link between two stations
present on the earth. These satellites can handle communication
up to large distances. But
it is impossible for a single geo-stationary satellite to cover
the whole earth and provide a
communication link. Due to curvature of earth the stations will
be out of sight after covering
some distance. If we want to cover the whole earth then we have
to put three satellites onto
the geosynchronous orbit. These satellites can cover the earth
if all are inclined at an angle
-
8/3/2019 Sati Communication
3/3
of 120oto each other.
The comparison of fiberoptics cable and copper wire is as
follows.
Fiber Optics1. Higher bandwidth than copper.2. Low attenuation,
repeaters are needed after 30 km.
3. Not being affected by power fluctuation, electromagnetic
interference, or power failures.
4. Not affected by acidic chemicals in the air.
5. Installation cost is much lower.
6. Do not leak light and are quite difficult to tap.
Copper Wire1. Can run several km without amplification, but for
every 5 km repeaters are needed.
2. Adequate performance and low cost than fiber optics.
3. No need of skill engineers to install copper wire.
4. Less electrical interfaces cost than fiber interfaces.
