No need for cumbersome formula calculations, just a ruler and two thin lines, you can draw a precise parabola! The drawing process is described in detail below. Parabola refers to the trajectory of a point in the plane to a point where the fixed point F and a fixed line L are equal. As shown in Fig. 1, the trajectory (or set) of a point in the plane to a point where the fixed point F and the straight line L of F are equal is called a parabola. This fixed point is called the focus of the parabola. This straight line is the guideline of the parabola. F is called "the focus of the parabola" and L is called the "parabola of the parabola." The distance from the focus to the parabola line is the "focal distance", denoted by P. P》0. The surface obtained by rotating the parabola with its axis of symmetry as 1800 is the paraboloid. It is generally possible to calculate the focus position from the caliber and depth. The focal length ratio of the parabolic antenna has a fixed formula: F/D=0.38-0.4, the common positive feed antenna focal length aperture ratio F/D is between 0.3 and 0.4, when F/D=0.38, the rotating parabolic antenna The best performance, the general product feedforward parabolic antenna mostly uses the focal length / aperture ratio, so as long as you know the antenna diameter D, according to the empirical formula F = 0.38D, you can roughly determine the focal length of the antenna. Similarly, knowing the focus (or focal length) and antenna aperture, you can find the parabola of the antenna. The attached table is the specific parameter of the Zhongwei positive feed antenna. Due to the use of a circular arc, the light waves at the edges will fall out of focus, and it is impossible to make the antennas that are out of the way. We already know that the points on the parabola are equidistant from the focus and focus. Moreover, the caliber and focal length of the finished large-diameter feedforward antenna are also available, so a precise parabola can be drawn according to this condition. Refer to the Zhongwei 1.80 m feedforward antenna for demonstration. The specific steps are as follows: The first step: find a flat open space of 3 meters square, draw according to Figure 4. The focus F, the vertex O, the guide line L, and the aperture AB of the 80 m antenna. If you make a larger paraboloid, you can choose the focal length and aperture according to the parameters in Table 1. The guideline L can also be replaced by a wooden strip. The vertex 0 to the focal point F can be replaced by a whole piece of wood board (width l220mm, length 2440mm) instead of (f11) 2440mm, which is placed on the vertex 0), so that the parabola can be drawn directly. On the wood board, in order to make a parabolic template. The second step: A-B randomly draws a plurality of horizontal lines parallel to the parabolic axis PF according to a certain distance (for example, l0cm or 5cm). The third step: find two thin lines or line rulers, the line can use 10 colors of colored pencils to make marks according to lcm distance, l0cm just use l0 colors (if there are conditions, you can use line ruler, the line ruler itself has size Then, then fix one end of the blue line FK in Fig. 5 to the focus F, and the other red line AK arbitrarily select a point between A and B, and fix it straight so that it is parallel with the drawn parallel line, FK and When the AK two lines intersect and the length values ​​are equal, the corresponding point is a point K on the parabola, which is drawn on the wood board. And so on, draw K', K" ... and so on to take more points on the AB line segment, you can draw an extremely accurate parabola. The resulting template accuracy can be compared with the Zhongwei antenna ! Note: Be sure to make the red line AK in the figure parallel to the axis. The intersection of the red line AK coin I3 blue line FK must be equal. The method of drawing a parabola as above does not require a formula. It is extremely simple and easy to operate. Anyone who can draw parallel lines and can understand the size will do it. The fourth step: draw a straight line between the painted parabola KG, and then cut it on the wood board, make a mold, use round steel, flat iron or stainless steel to make the antenna frame, the antenna surface can be barbed wire, stainless steel mesh, etc. Material production, its production method can find a lot of tutorials online, and will not go into details here.
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