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Instructions | Imagine you are out in space, looking down on the Earth. There are dozens of clusters of satellites encircling the earth in "geostationary orbit". Each cluster contains satellites which are so close to each other (usually less than 100 km apart) that their signals appear to arrive on earth from a single point in space. This point is usually specified by its angular position relative to the prime meridian which passes through Greenwich, UK. For clarity, only three satellite clusters are shown here. Satellite clusters are approximately 3 degrees apart. If they were closer together, it would be difficult to focus on one without receiving an interfering signal from the two adjacent. To receive a useful signal from one satellite cluster, the dish must be aligned to an accuracy of no greater than one degree and preferably less. The larger the dish, the smaller the effective focal angle, and the greater the accuracy which is required. Although it is possible to align a dish without the use of a meter, you could spend a long time fiddling. What is your time worth? FAQ: "I get a strong signal but no picture. What is wrong?" A. Your dish is probably aligned on the wrong satellite. Click HERE. The yellow blobs represent three of the satellite clusters which transmit TV programmes back down to earth. The Hot Bird satellites are 13 degrees east of the Prime Meridian, Astra-1 satellites at 19.2 degrees and Astra-2 satellites at 28.2 degrees (plus Eurobird at 28.5) for Sky Digital and other English language programmes. They are 22300 miles above the African equator. See map below. The numbers refer to the angles measured from the centre of the Earth between a line passing through 0 degrees on the Prime Meridian (off the African coast) and another line from the centre of the Earth and passing through each satellite. Here are the satellites sitting 22300 miles above the equator (on the latitude line of 0 degrees). The azimuth angle is NOT the compass angle, although, as the UK is very close to the Prime Meridian longitude line of 0 degrees, the compass angle is often a reasonable approximation if you are in eastern England. Elsewhere it's not true, as you can see from the map. Look at Vatican City in Italy. Hot Bird (at 13 degrees) is actually directly south of the Vatican so pointing your dish 13 degrees east of south on your compass will miss the satellite by thousands of miles! Read about longitude and latitude here: http://www.nationalatlas.gov/articles/mapping/a_latlong.html and http://www.socialstudiesforkids.com/articles/geography/equatorprimemeridian.htm The elevation angle of a satellite is the angle measured between the horizon as you see it and a line drawn between you and the satellite. Because the Earth is round, the angles in the UK are typically 20 to 26 degrees. In Europe 26 to 36 degrees and, of course, if you are standing on the Equator in Africa, the satellites are almost directly above you at 90 degrees. Use an az/el calculator to determine the satellite location relative to your lat/long position. You can get your lat/longitude by typing in your postcode here: Use it in this elevation calculator for Astra 2A ©2004-2017 SatCure
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