Satellite dish installation

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Typical satellite dish installation

A typical home satellite dish installation for receiving geostationary satellite transmissions consists of a satellite dish, a LNB and a receiver/decoder.

[edit] View direction

To receive a transmission from a satellite, a satellite dish must be pointed exactly to the satellite's position in space.

The view direction of a satellite from a location on Earth is determined by two angles: altitude and azimuth. These angles depend on the receiver's latitude, longitude, and the satellite's geostationary longitude.

For satellites that are on a longitude equal to that of the receiver, the altitude can be found with a simple geometric construction:

For different satellite and receiver longitudes, the azimuth can be found by extending the previous figure:

Altitude (A) and azimuth (a) relative to true north can be calculated from latitude (φ), longitude (λ) and satellite longitude (λ_s) with these formulas:

$\Delta\lambda=\lambda - \lambda_s\,\!$

$A\approx\arctan(\frac{6.612\cos(\phi) \cos(\lambda)-1}{6.612\sqrt{1-\cos(\phi)^2 cos(\Delta\lambda)^2}})$

$a=180+\arctan(\frac{\tan(\Delta\lambda)}{\sin(\phi)})$

[edit] Skew

Several satellites transmit with linear polarization, with polarization planes usually parallel to and at right angles to Earth's axis. The dish's polarization must match the signal's polarization, otherwise cross polarization will interfere with signals from the opposite polarization. The requirements for this match are quite narrow and must be accurate to less than one degree.

If receiver and satellite longitudes are different, the skew (rotation) of the receiver must be adjusted.

The skew angle (s) for adjusting the LNB can be calculated with this formula:

$s=-\arctan(\frac{\sin(\Delta\lambda)}{\tan(\phi)})$