Antennas for satellite television (called the common people – "Satellite dish") There are two types: direct focal and offset.
They differ in shape mirror receiving and oriented electrical and geometrical axes antenna. In direct focal antenna mirror is made in the form of a paraboloid, and antenna axis collinear with the geometric axis of mirror. We offset antennas mirror is performed in the form of an ellipsoid, and the electrical axis of the antenna is different from the geometrical axis of the mirror about 25-30 degrees.
Setting satellite tv has certain features depending on the selected antenna. for example, due to a different location converters (to direct focal antennas He sent down, and to offset - on the contrary, up) the external environment, precipitation, wind, etc., may influence the quality of the received signal. Therefore, sometimes to improve the quality of the received signal and issues, associated with power failure, fed antennas may further be equipped with gas generators for continuous supply of electricity.
Besides, Converter arrangement affects the size of the mirror. So, in antennas direct focus converters obstruct some of the received antenna area (about 5%). The offset dish is no shortage of such. Therefore, the antenna with a diameter smaller mirrors 2 m doing offset, and more - with a direct focus.
To make the best satellite tv, should carefully monitor the integrity of important components of the antenna, especially converter. In direct focal antennas converters can be used with a reduced tightness system or even without it, as they Converter, as discussed above, sent down. The offset antenna to the converter must be, conversely, apply additional protection against ingress of water.
Differences in the structure of the antenna is taken into account when used in the northern regions. for example, offset dish here can not be lowered to the desired small angle of elevation. So, when satellite elevation angle in 5 degrees, antenna must be directed approximately 20 degrees below the horizon. But for antennas with a large diameter mirror (eg, antenna "Supral" with about two meters in diameter) ensure that it is not possible because of the design of the antenna itself. The maximum angle of inclination from them is not more than 12 degrees. In such cases, when installing an antenna for deploying 180 degrees, to achieve the required performance. true, it requires some refinement fasteners.
