|
 |
Communication
Satellite
as a relay station, is out in space. |
|
 |
Revolves at the same (angular)
speed as the Earths rotation (geostationary), 35,840 KM above the equator
(in the Clarke Orbit) |
|
 |
The satellite receives signal from
a station on Earth (Uplink)
and
Send the signal back to Earth
(Downlink)
with
A very wide coverage area (Foot
Print)
|
|
 |
Example :
Signal broadcast to Earth (Downlink) from the
satellite Palapa C2, with coverage area (Foot Print) from China to New Zealand
|
|
| A Satellite consists of:
Tens of Transponders made up of antennae and
computers
Solar energy Power Source (solar cell) and
battery
Small Booster Rockets and so on
|
 |
|
| Classification
of Downlink Frequency:
L band (950 - 2150MHz)
S band (2.5 - 2.6GHz)
C band (3.7 - 4.2GHz)
KU band (10.95 -12.75GHz)
KA band (18.3 – 22.2GHz)
For Television, C and KU band
frequencies are the most popular |
 |
|
| To
save on frequency usage
Signals are polarized
into
vertical and horizontal
waves (Linear polarization)
|
 |
|
| Or
into Right
hand (clockwise) and Left
hand (anti-clockwise) circular rotation (Circular polarization).
Most of French and Russian satellites use
circular polarization
|
 |
|
 |
Television broadcast reception
from satellite is called
TVRO System
(Television Receive Only)
|
|
| 2 characteristics of satellite
signal worth noting:
Signal transmission relatively weak because:
Signal transmitted from far in space
Very limited power source
Signal is of micro-wavelength (giga Hertz
frequency), whose characteristics are similar to those of light waves.
|
Generally,
the way to receive weak satellite signal is:
To use a reflector plate in the
shape of a parabolic curve
And then focus the signal so
that it is strong enough to be processed.
|
|
