Pagina 145 - TELE-satellite-1207

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145 —
06-07-08/2012 —
TELE-satellite International —
you connect your receiver to your PC you
will end with a fully-fledged information
centre that leaves nothing to be desired.
Language barriers can easily be over-
come with the help of images and the
Internet as well as TELE-satellite maga-
zine are valuable sources of information
for satellite enthusiasts.
Elevation towards
the south
One of the determining factors for the
successful installation of a polar mount
antenna is the mast which needs to be
inclined as precisely towards the north
from its vertical position as possible. You
may always correct a slight north-south
deviation at a later stage when fine-tuning
the complete system, whereas an impre-
cise east-west alignment can only be
adjusted by moving the antenna mast.
Another underlying condition is know-
ing the precise geographic longitude and
latitude of the antenna location – at least
everything except the decimal places. As
mentioned in the introduction these data
can be obtained from specialists in the
field or from friends owning a handheld
GPS device. The geographic longitude
is of particular importance, as it plays
a crucial role for calculating the correct
elevation and determining the south-
ern direction. A compass should only be
relied on as general guidance for identi-
fying a southern direction, as its use it
too error-prone.
It is much better to look for a satel-
lite that is positioned as closely to the
geographic longitude as possible. This of
course requires a TV or monitor to verify
the result and to avoid pointing the
antenna to the wrong satellite (as sat-
ellites can be positioned rather close to
each other). Fig. 5 indicates the correct
angles which are required for the calcu-
lations that follow.
M = centre of the earth
N = north pole
P = location of the antenna
φ = geographical latitude of the location
R = 6,371 radius of the earth
MS = 42,16 radius of the satellite’s orbit
ε = elevation
Fig. 5
P`S = 42,16 – 6,371.cosφ
ε = µ −φ
This means the elevation ε towards the
south is:
(Note that the radii of the earth and
the satellite’s orbit are shortened in the
Figure 6 shows the angle by which the
rotation axis for the antenna has to be
inclined towards the north so that it is in
parallel to the pole-to-pole axis.
Fig. 6
Inclination towards the north against
the horizontal level is: φ (conforms to
geographical latitude)
Inclination towards the north against
the horizontal level is: γ = 90 - φ
Inclination of the
antenna towards
the satellite
Once the rotating axis is inclined to
the north by the appropriate angle the
antenna has to be rotated downwards
by the angle δ against the right angle
towards the rotating axis, so that it
‘looks’ directly to a satellite that is south
of the location.
Angle δ is defined as declination
reception range
Naturally, a general calculation exam-
ple like the one above cannot take into
account local factors such as buildings,
trees etc. that might influence recep-
tion at the respective location. The only
value that can be calculated is the maxi-
mum angle that is limited by the horizon.
This angle is calculated from the south
towards east and west.
The maximum reception range ω
depends on the geographic latitude of
the location of the antenna, gradually
decreases the further north the loca-