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Calculating satellite dish direction The view-direction of a satellite dish depends on the dish position on the Earth and on the satellite position in the Clarke belt. THe view-direction is determined by two angles: altitude (or elevation) and azimuth. Proper combination of these two angles is required to exactly point the desired satellite, from which the dish will receive the electromagnetic radiation that it will then convert to electric signal sent to a decoder, which will eventually convert it into an audio-video signal and transmit it to a TVset. Image File history File linksMetadata Satellite-dish_cropped. ...
Image File history File linksMetadata Satellite-dish_cropped. ...
Earth is the third planet in the solar system. ...
A satellite is any object that orbits another object (which is known as its primary). ...
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Basic Definition In geography, the elevation of a geographic location is its height above mean sea level (or some other fixed point). ...
Azimuth is the horizontal component of a direction (compass direction), measured around the horizon toward the East, i. ...
Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ...
Radiation has a variety of different meanings. ...
A decoder is a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. ...
See TV (disambiguation) for other uses and Television (band) for the rock band European networks National In much of Europe television broadcasting has historically been state dominated, rather than commercially organised, although commercial stations have grown in number recently. ...
Satellites used to broadcast TV signals are positioned in the Clarke belt, an imaginary "belt" which surrounds the Earth and lies over the equatorial plane; the distance between the belt and the Earth is determined in such a way that any object moving along it will have two main features: Earth is the third planet in the solar system. ...
In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of gigantic radius, concentric with the Earth. ...
- it can remain in its position without requiring any engine to defeat the gravity attraction (apart for minor orbit correction required to compensate atmosphere drag)
- it appears always still in the same position in the sky to an observer located on the Earth surface.
Being the satellite stationary with respect to the Earth ("geo" in Greek language), this kind of satellites are called geostationary, and they can then be "viewed" by a parabolic-dish with fixed heading. Gravity is a force of attraction that acts between bodies that have mass. ...
In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...
Earth is the third planet in the solar system. ...
Graphical explanation of Elevation and Azimuth First picture shows how the Elevation angle is determined:
 Image File history File links Parabola-alt. ...
The Altitude/Elevation angle (ALT) depends on the observer's latitude (LAT), e.g. its angular distance from the equator (the horizontal line in this picture). At a first glance, it could look like, from this figure, that the dish should be pointed down rather than up; actually, the "reference line" is not just the equator, but the horizon line: in this picture, it is represented by the line which "touchs" the Earth exactly in the point where the dish/observer is. So, the Elevation angle is calculated with respect to this line. If the Latitude is greater, the Altitude will be lower, and viceversa. If the dish is positioned exactly on the equator (LAT=0 degrees), its Elevation must be 90 degrees to point the satellite; viceversa, if the dish is at the north pole, its Elevation should be 0 degrees; but actually, a dish positioned at north pole couldn't probably view any geostationary satellite, which would result "shadowed" by horizon line; in theory, a dish at north pole, with elevation = 0, could only see an object in equatorial orbit only if it was located at infinite distance. Latitude, usually denoted symbolically by the Greek letter φ, gives the location of a place on Earth north or south of the Equator. ...
The equator is an imaginary circle drawn around a planet (or other astronomical object) at a distance halfway between the poles. ...
Horizon The horizon is the line that separates earth from sky. ...
A degree (in full, a degree of arc, arc degree, or arcdegree), usually symbolized °, is a measurement of plane angle, representing 1ï¼360 of a full rotation. ...
A degree (in full, a degree of arc, arc degree, or arcdegree), usually symbolized °, is a measurement of plane angle, representing 1ï¼360 of a full rotation. ...
Infinity is a word carrying a number of different meanings in mathematics, philosophy, theology and everyday life. ...
Next picture shows how the Azimuth angle is determined:
 Image File history File links Orientamento-parabola-long. ...
If the observer longitude (LONG) and the satellite longitude (SATLON) are the same, they will lie on the same meridian, thus the dish must be pointed exactly to the south (azimuth=180 degrees) to see the satellite. If the longitudes are different, instead, as shown in the picture, the required azimuth will differ from 180 degree, as much as longitudes differ. Longitude, sometimes denoted by the Greek letter λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. ...
Meridian is: Meridian (astronomy): an imaginary circle perpendicular to the horizon. ...
A compass rose with South highlighted South is most commonly a noun, adjective, or adverb indicating direction or geography. ...
A degree (in full, a degree of arc, arc degree, or arcdegree), usually symbolized °, is a measurement of plane angle, representing 1ï¼360 of a full rotation. ...
Besides, Altitude and Elevation of the dish depends one on the other, so the final formulas needed to determine them are slightly complex:
v1 = 6.612 * cos(LAT)*cos(LONG-SATLONG)-1 v2 = 6.612 * sqrt( 1-(cos(LAT)^2) * (cos(LONG-SATLONG))^2 ) ELEVATION = atan(v1/v2) AZIMUTH = 180 + atan( tan(LONG-SATLONG) / sin(LAT) ) POLARIZATION = -atan( sin(LONG-SATLONG)/tan(LAT) ); - LONG = dish longitude;
- SATLONG = satellite longitude;
- LAT = dish latitude.
- sqrt means Square Root
Graphical explanation of dish polarization or skew In case the satellite longitude is very different from dish longitude, it maybe necessary to adjust its skew too; this adjustment is usually very slight and it's due to polarization plane of the dish being rotated when changing azimuth and elevation of the dish itself, as shown in this picture: In electrodynamics, polarization (also spelled polarisation) is a property of waves, such as light and other electromagnetic radiation. ...
 Image File history File links Dish-skew. ...
The satellite polarization plane is indeed parallel to Earth axis, and so must be the dish polarization to allow proper signal reception.
This picture shows in detail how the dish should be moved to fix skew:
 Image File history File links Skew1. ...
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