TELE-satellite International — The World‘s Largest Digital TV Trade Magazine
1 -12/2012
TELE-satellite HISTORY
TELE-satellite in 2002
Discussions regarding „out-of-
footprint“ reception are almost as
old as satellite transmission itself.
However, there has never been a
reasonable explanation for the fact
that ASTRA can be received in some
parts of South America or that TELE-
satellite reader K. Schumacher in
southern Brazil can receive the
analog signals of ASTRA and EUTEL-
SAT almost noise free with his self-
assembled 8 m antenna. The digital
signals, on the other hand, seem
to be unreachable with his equip-
ment. TELE-satellite International
contributor Vladimir T. Lemos is an
engineer for spaceship antennas in
Washington, D.C. and has addressed
this question.
Out-of-footprint reception is due in
part to the overspill of electromag-
netic energy radiated from the satel-
lite antenna onto a region beyond that
of the intended service area. On a day
with a clear sky, there is higher over-
spill because more power reaches the
ground antenna. Since most satellites
are designed to provide, under bad
weather conditions, a minimum power
flux density at the edge of the coverage
area, there is excess power available for
reception when the weather is good.
The electromagnetic energy is also
spread outside the service area when
there is spillover from the feed in a dual
reflector antenna system. In a single
reflector antenna, the feed spillover is
directed towards outer space. Note the
distinction between overspill and feed
spillover. Figure 1 shows feed spillover
in the PLANK satellite dual reflector
antenna system: in a Gregorian con-
figuration, the feed points towards the
small secondary antenna and the large
primary 1.5 meter reflector is directed
towards the Earth.
Overspill suggests that large ground
paraboloidal antennas could receive
weaker signals because they would
provide higher gain at communication
satellite frequencies. However, even a
large antenna would not guarantee you
could get unintended satellite service
in your backyard. Overspill accounts
in part for the out-of-footprint recep-
tion reports, but mostly for the cases
where the ground antenna is located
near the boundaries of a coverage area.
Someone in central Africa with an over-
sized Ku-band antenna could pick up
signals from EUTELSAT Atlantic Bird 2
European coverage area. If there is too
much overspill, the signals of adjacent
service areas with the same frequency
and sense of polarization interfere with
other. At lower frequencies, the prob-
lem is worse because the radio waves
are spread over a broader area. Figure
shows spillover interference in radio
astronomy band: overspill from a wire-
less service operating in an adjacent
service area adds noise to the system.
In order to provide service over an
irregular geographical region that is
What’s behind
out-of-footprint reception?
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
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