As the window of satellite TV, the satellite antenna system occupies a very important position in the cable TV system. The quality of the satellite antenna and the focus of its feed source play a vital role in the quality of satellite programs.
Seen in the actual problems of the antenna feed system, this article wants to talk about my views and suggestions on the focusing of the satellite antenna and its feed. In practice, satellite antennas generally use rotating parabolic antennas. Rotating parabolic antennas have two very important characteristics:
(1) The electromagnetic wave emitted by the focal point is reflected by the parabolic surface, and the propagation direction is parallel to the axis; on the contrary, the electromagnetic wave parallel to the axis is reflected by the parabolic surface and converges at the focal point.
(2) When the electromagnetic wave emitted by the focal point is reflected by the parabolic surface and reaches the parabolic antenna aperture plane and any of its parallel surfaces, all ray travels are equal, that is, the spherical wave emitted by the focal point is converted into a plane wave after being reflected by the parabolic surface, and vice versa. The electromagnetic wave transmitted by a synchronous satellite located about 3600km above the earth to a certain point on the ground can be regarded as a parallel ray (plane wave). When the parabolic antenna is aimed at the satellite, or the axis of the rotating paraboloid is adjusted to coincide with the direction of the electromagnetic wave (the angle is 0 °), all electromagnetic waves reflected by the paraboloid will converge on the focal point. This shows that to accurately and effectively receive satellite TV signals, the first two tasks are satellite antenna alignment and focusing. In practice, people often only focus on the satellite antenna alignment and neglect the focus. In fact, the antenna focus is equal to or even more important than the satellite alignment. When the feed port deviates slightly from the focus position, the feed signal will be greatly reduced. Small, this is conceivable. Therefore, it is necessary to pay attention to the focusing work of the satellite antenna, that is, to accurately adjust the feed port to the focal position of the parabolic antenna. ?
The method of calculating the focal position of the parabolic antenna is as follows: suppose the diameter of the parabolic antenna is D, the depth (the distance from the vertex of the parabolic surface to the center of the aperture plane) is h, and the focal length (the distance from the vertex of the parabolic surface to the focus) is f.
f = D216h (1)
In practice, D and h can be obtained by measurement, and then f can be obtained from equation (1).
Knowing the characteristics and working principle of the parabolic antenna and the calculation method of the focal position are very important to us, but we must pay attention to the difference between the actual antenna and the theory. The so-called rotating parabola is a parabola formed by a parabola rotating around its symmetry axis. The parabola must be a trajectory curve formed according to its definition. However, in practice, for various reasons, the actual parabolic antenna often has some discrepancies with the ideal parabolic antenna. For regular antenna manufacturers, from the aspects of design, material, structure and manufacturing process, the standard and accuracy of the antenna shape are guaranteed. However, due to the serious fish-eye mixing phenomenon in the satellite antenna market, many informal antenna manufacturers have a large number of non-standard The emergence of non-standard antennas has caused a lot of trouble to satellite TV windows. Some people and marketers who are engaged in the design and installation of cable TV systems think that satellite antennas are just a pot, and anyone can produce them. Therefore, the actual satellite antennas do not exist. There are few problems, and the following four situations can be summarized: 1) The feed bracket is irregular and the length of the support rod is not suitable, so that the feed port cannot be accurately placed in the focus position. 2) Due to manufacturing process problems, the antenna is deformed into a non-standard parabolic antenna. 3) Due to material or structural problems, the antenna deforms during transportation or installation and use. 4) Due to design problems, it seems to be a parabola, but it is not actually rotated by a standard parabola. For the first case, as long as the paraboloid is relatively standard, the feed frame is modified to meet the requirements, and the feed port can be adjusted to the focus position to obtain good results. For the cases 2) and 3), if the deformation is not serious, find the focal length according to (1), put the feed port in the focus position, and adjust it slightly to obtain satisfactory results. When the deformation is severe, the electromagnetic waves converging on the focal point are greatly reduced, and the effect after focusing is very poor or even unwatchable. For case 4), there is no focus, and it is a fake and inferior product and cannot be used. For the antenna installer, when purchasing a satellite antenna, the standard qualified antenna and the above-mentioned 4) antenna are usually difficult to identify with the naked eye. The antenna standard can be judged by the following methods: 1. Whether it is a regular manufacturer. The second is to compare with standard antennas of the same caliber. Aim the antenna at the same satellite, use the same feed, high-frequency head and satellite receiver, put the feed at the focal position, receive the same set of programs, compare the signal strength, the same or close is better, otherwise it is inferior.
Let me talk about my own suggestions:
1) The radio and television department should formulate strict standard requirements and detection methods for satellite antennas.
2) The product quality supervision and inspection department shall strictly follow the relevant quality standards and indicators, conduct scientific inspections on the quality of the satellite antennas, ban counterfeit and shoddy products, and impose penalties. 3) As a buyer, you must purchase qualified products produced by regular manufacturers and tested by the quality inspection department. 4) As the design and installation unit of the cable TV system, it is necessary to have its own set of satellite antenna quality detection or judgment methods to make the fake and inferior antenna no root. 5) The design and installation unit of the cable TV system should pay attention to the focus of the feed, and the feed port must be placed at the focal position of the parabolic antenna.
BLPS laser safety protective device is designed for personal safety used on hydraulic bender.
The dynamic test technology it used has passed the Type 4 functional safety assessment by TUV, and get the national invention patent. The product reaches the advanced technological level of similar products.
BLPS laser safety device provides protection zone near the die tip of the bender to protect fingers and arms of the operator in close to the upper mold die tip. It is the most effective solution so far to preserves the safety and productivity of the bender.
Press Brake Protection,Laser Safety Guard Device,Laser Guarding Device,Press Brake Laser Guard,Press Brake Guarding Systems,Press Brake Guarding
Jining KeLi Photoelectronic Industrial Co.,Ltd , https://www.sdkelien.com