The parameters for adjusting the focal length of the satellite antenna mainly include the three parameters of azimuth, elevation, and polarization. The azimuth and elevation can be calculated by the latitude and longitude of the receiving location. The polarization angle is set according to the signal polarization mode of the receiving star, so these three parameters are relatively easy to adjust to the best state. There is also a parameter that people can easily ignore, that is, the focal length of the antenna. Generally speaking, if the antenna is produced by a famous manufacturer, as long as it is correctly installed according to the installation instructions, the focal length of the antenna is basically correct. But if it is some miscellaneous antennas, it is difficult to say, especially for small-caliber antennas, how to make the feed port accurately adjusted to the focal position of the antenna theoretical design is the key. There are three situations that cause the feed port to deviate from the focus position:
1. The geometric dimensions of the support rods of the feed tray are inconsistent, the lengths are different, and the fixing holes are biased.
2. The tightening screws of the antenna lobes are different during the installation process, deforming the antenna into a non-standard parabolic antenna.
3. Miscellaneous antennas deviate from their focal length due to design and processing problems.
For example, for a 1.5-meter feed-forward parabolic antenna, its F / D (Focal Diameter Ratio) is usually about 0.4. From this conversion, the design value of the focal length of this antenna is about 0.6M. When installing and debugging the antenna, use a tape measure to measure the focal length to see if it is around 0.6 meters.
The following methods can be used to quickly and accurately adjust the focal length. After tightening most of the screws of the antenna, the three screws that fasten the feed tray are temporarily not fastened, so that they have a certain degree of rotation. Turning the feed tray to the right or left when commissioning the focal length will make the focal length smaller, as shown in the figure. Because the length of the support rod is fixed, the rotation of the feed tray can ensure that the feed port is always on the geometric center axis of the pot. When the support rod is as shown in Figure A, the focal length is the largest. In the two cases of Figures B and C The focal length becomes smaller.
When adjusting the focal length, you can switch from the maximum focal length (Figure A) to the minimum focal length (Figure B, C), and find the best state during the process of right-hand or left-hand feed plate. This can be judged from the received signal quality index. From Figure A to Figure B and C, there must be a point where the signal indicator is the best, and at this point the signal indicator becomes worse at both ends.
Of course, in order to accurately adjust the antenna to the best state, it is also important to fine-tune the azimuth, elevation, and position of the high-frequency head relative to the feed plate. You can advance or remove the high-frequency head. Turn the high-frequency head left and right to find the best position. After all these are carefully adjusted, the antenna is adjusted.
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