First, understanding the quasi-parabolic and parabolic line
Parabola is a plane to a fixed point F and line a distance equal to the L locus of points. Shown in Figure 1, the plane to a point F and F is a fixed straight line, but the distance L equal to the locus of points (or sets) that is called a parabola. This point is called the focus of the parabola, this line is the parabola given the alignment. F is called "the focus of the parabola", L is called "quasi-parabolic line." Focus to the parabola of the quasi-line distance to "focus quasi-gap", with P said. P> 0.
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Second, the parabolic
Parabola with its axis of symmetry of the axis of rotation 1800 to get the surface is parabolic.
Third, the manufacture or installation of the first wife to find the parabolic antenna, the focus of the parabola
Generally start from the diameter and depth to calculate the focus position. Parabolic antenna has a fixed focal length than the diameter of the formula: F / D = 0.38-0.4, the common focal length is fed antenna aperture ratio F / D at 0.3-0.4, and when the F / D = 0.38, the rotating parabolic antenna best performance, the general product is fed mostly used parabolic antenna focal length / diameter ratio, so long as we know the antenna diameter D, according to empirical formula F = 0.38D, we can roughly determine the focal length of the antenna. Similarly, knowing the focus (or focal length) and the antenna aperture, we can obtain the parabolic antenna. Schedule is the defender is the specific parameters of the antenna feed.
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Fourth, the success of home-made dish is to draw an accurate parabola
As a result of the arc, leading to the focus falls on the edge of the light gathered outside, do so out of the antenna is not possible to offset income.
We already know a point on the parabola to its focus on alignment and the same distance. But also with the finished product being fed large-diameter antenna aperture and focal length, so this condition can be accurate to draw a parabola. Defender fed reference antenna is 1.80 meters do demonstration, follow these steps:
The first step: find a 3-meter flat space, draw l. Figure 4 80 m antenna of the focus F, vertex O, alignment L, diameter AB. If you make a larger dish, in accordance with the parameters in Table l to select the focal length and aperture. Alignment L can also be used instead of wood, vertex 0 to the focus F can be a block of wood panels (width l220mm, length 2440mm) vertically instead of (f11) 2440mm edge on this vertex 0), so the parabola drawn directly In the wood board, and in order to produce parabolic template.
Step Two: A-B in accordance with a certain distance between the free (for example l0cm or 5cm) draw a number of horizontal axis with the parabola parallel to PF.
The third step: find a thread or two-foot line, 10 colors available online lcm from the well marked in accordance with the brush, l0cm just spent l0 colors (if the conditions can be line-foot, wire-foot size itself a), then the blue line in Figure 5 FK's a fixed focus F, the other root of the red line in the A-B AK arbitrarily choose a point between the fixed and straightened so that parallel lines drawn parallel to, FK and AK value of the two lines cross and length equal to the corresponding point on a parabola is K, in the wood panel painting on this point. Again and so on, draw K ', K "... ... so tired to take the point on the line segment AB enough, you can draw an extremely accurate parabola. Accuracy of this template can be made comparable with the defender antenna !
Points to note: make sure the red line graph with axes parallel to the AK, AK coin I3 red blue line intersection must ensure that the FK values are equal. As the method does not require painting parabolic equation, very simple, easy to operate, can draw parallel lines, the size of people will be able to read to do.
Step four: in the parabola drawn a straight line drawn between KG and then cut out of wood board, made a mold, with round, flat iron or stainless steel frame and other materials to do the antenna, the antenna surface can be used barbed wire, stainless steel net materials, their production methods can be found in a large number of online tutorials, not repeat them here.
