A number of satellites have been launched into orbit around the earth. They sit in a circle above the equator at a distance of 36,000km. This position allows them to remain in the same relative position in the sky.
To a viewer on Earth, they do not appear to move.
Each satellite has the ability to receive signals transmitted from Earth and to re-transmit them back to Earth over a wide area. The satellite on-board equipment which does this is called a Transponder. A satellite can have several transponders - typically 16. On the ground, large transmitting dishes are used to "uplink" the programmes to each satellite. Each transponder of each satellite beams the programme back down so that it reaches an area designated the "footprint". This is the area where the signal is strongest. The signal becomes weaker towards the edges of the footprint.
To receive a signal you need a dish. This acts as a curved mirror and focuses the weak signal at a point in front of the dish where an
"LNB" sits
