Thrane&Thrane sailor 90, Installation Manual

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1
Chapter 1
System Units
General information
Satellite TV reception, general information, footprints
Satellite orbits
All TV-satellites move in so called geostationary orbit 36.000 km above the
Earth's equator. At this specific altitude their angular velocity matches the
Earth's exactly and make them appear motionless in the sky.
When viewed from the northern hemisphere the satellites appear along an arch
with the satellite due south at the top.
The necessary separation between satellites depends on the frequency and the
size of the antennas and is usually 3°. A large number of satellites can be co-
located in the same position as long as
they transmit on different frequencies.
Co-located satellites are allowed to
deviate 0,1 degrees within their position,
which equals to a cube with a side of 73
km. At position 19.2 deg East (Astra 1) for
instance, there are actually 5 satellites
within the same position.
The satellites get their signals from an
uplink station. The satellite that
receives the signal shifts the
frequency down to about 10-
12 GHz, amplifies it and
transmits it back towards
earth by what is called
transponders. The satellites
electrical power comes from solar
panels, and the satellite is kept in
position by small jet-motors mastered
by ground-control. The actual life-span
of a satellite mainly depends on fuel
left for positioning jets.