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Technology In The Home |
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Aligning the dish for Astra 2 & Eurobird at 28.2 degrees east of south |
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Dish elevation in the UK varies from around –2 degrees (minus) in the north of Scotland to around +5 degrees along the south coast of England. Whilst this sounds different to the actual elevation of around +28 degrees is because the dishes have a built in offset angle which compensates for this angle. Depending on the dish manufacturer, a dish has an approximate offset angle of around 23 degrees. |
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The satellites relevant for the reception of satellite TV and radio programmes are positioned in a geostationary orbit in the so-called "Clarke Belt", which can be found at an altitude of 35.803 km directly above the equator. The satellites positioned there are in analogous motion with the earth's own rotation, so that they appear to be stationary above a constant point on the earth's surface. This is the basis that allows us to constantly receive satellite signals by means of a fixed, mounted antenna on the earth surface. Dependant on the satellite's position in this orbit, e.g. ASTRA at 28.2° East, and the position of the satellite antenna relative to the East/West and to the North/South direction, two values can be found which are essential in order to position the antenna correctly for the desired satellite, viz. the "azimuth angle" and the "elevation angle". Azimuth is the angle relating to the horizontal positioning of the dish. The angle is expressed in terms of degrees, with North = 0 degrees, South = 180 degrees. Elevation is the angle above the horizon, and is also expressed in terms of degrees. This is the angle by which the dish must be "tilted" in relation to the theoretical horizon, in order to position it precisely for the desired satellite. |
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As you can clearly see from the illustration on this page, parabolic antennas for satellite reception can also be placed at ground level close to the house (e.g. in the garden, etc.), and only in rare cases is it actually necessary to mount the antenna on the roof. Even in cases where the parabolic antenna cannot be installed in the garden, because there is no straight line of sight to the desired satellite, we recommend that you check whether a wall mount may be used to attach the dish antenna to a house or garage wall. On the one hand, this simplifies the installation, and on the other hand it makes the dish more easily accessible. The illustration below shows how well placed the key satellites, ASTRA and EUTELSAT are for the direct reception of satellite TV signals. The orbital positions of these satellites provide extremely favourable elevation angles for reception in Germany. For example, the elevation angle required to receive the signals from the ASTRA satellite at the 19.2° East position varies between approx. 28° (in the North) and approx. 35° (in the South) within Germany. Therefore, one usually requires only a few metres space (clearance) between an antenna and an obstacle in order to ensure a free line of sight to this satellite (see table below).
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