WHAT IS
SATELLITE?
A Satellite is a
solid object which revolves around some heavenly body due to the effect of
gravitational forces which are mutual in nature. We can categorize satellites
in two types, namely Passive Satellites and Active satellites. Passive
satellites are not like active satellites. Even a moon can be a passive
satellite. Thus passive satellites are relay stations in space. A passive
satellite can be further subdivided into two types, namely Natural satellites
and artificial satellites. A moon is a natural satellite of earth. But
spherical balloon with metal coated plastic serve as artificial satellites.
Active satellites are complicated structures having a processing equipment
called Transponder which is very vital for functioning of the satellite. These
transponders serve dual purpose i.e. provides amplification of the incoming
signal and performs the frequency translation of the incoming signal to avoid
interference between the two signals.
All ABOUT SATELLITE COMMUNICATION
The
term Satellite communication is very frequently used, but what is satellite
communication? It is simply the communication of the satellite in space with
large number of earth stations on the ground. Users are the ones who generate
base band signals, which is processed at the earth station and then transmitted
to the satellite through dish antennas. Now the user is connected to the earth
station via some telephone switch or some dedicated link. The satellite
receives the uplink frequency and the transponder present inside the satellite
does the processing function and frequency down conversion in order to transmit
the downlink signal at different frequency. The earth station then receives the
signal from the satellite through parabolic dish antenna and processes it to
get back the baseband signal. This baseband signal is then transmitted to the
respective user via dedicated link or other terrestrial system. Previously
satellite communication system used large sized parabolic antennas with
diameters around 30 meters because of the very faint and weak signals received.
But nowadays satellites have become much stronger, bigger and powerful due to
which antennas used have become automatically smaller in size. Thus the earth
station antennas are now not large in size as the antennas used in olden days.
A satellite communication system operates and works in the millimeter and
microwave wave frequency bands from 1 GHz to 50 Ghz. There are various
frequency bands utilized by satellites but the most recognized of them is the
uplink frequency of 6 Ghz and the downlink frequency of 4 Ghz. Actually the
uplink frequency band is 5.725 to 7.075 Ghz and the actual downlink frequency
band is from 3.4 to 4.8 Ghz. The major components of a Satellite Communication
system is spacecraft and one or more earth earths.
