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.

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