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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Production of VHF antenna YAGI. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / VHF antennas Any radio amateur, especially a beginner, starting to manufacture a "wave channel" antenna, immediately faces the problem of how to most accurately embody all dimensions in metal. Manufacturing accuracy should be quite high for the 144 MHz range - ± 1,5 mm, for the 432 MHz range - ± 0,5 mm The more accurately the antenna is made, the higher its parameters will be. The usual homemade set of locksmith tools - a drill, scissors and a hacksaw for metal - does not contribute to the quality manufacture of the antenna. with long traverse This has been verified in the manufacture of several antennas DJ9BV - 13 elements at 144 MHz and F9FT - 21 elements at 432 MHz. All of them were obtained with high accuracy. Required minimum tools. - hand drill (mechanical) - you "feel" it better;
Additionally, a marking "field" is required, which can be a piece of a flat rail channel of suitable length. The SC is shown in Figure 1, it is made as follows. Two pieces of rolled metal (a circle or a hexagon) are taken with a diameter of 50 ... 55 mm l \u80d 100 0,5 mm with even ends, and an axial hole is drilled on a lathe, the diameter of which is XNUMX mm larger than the diameter of the traverse. Be sure to check whether the blanks pass freely along the entire length of the traverse
It is possible that the traverse pipe will be slightly dented somewhere, then the gap of 0,5 mm will have to be increased to 1 mm, or the pipe should be straightened with a mallet. If the workpieces passed freely along the traverse, support strips 120 .. 150 mm long are welded to them in the center. Before welding in the middle of the SC, you need to drill and cut an M6 8 mm thread for the lock screw. The screw itself must have a handle that is easy to use and must have a conical end. Only such a screw ensures a clear and soft fixation of the conductor on the traverse in the right place. Next, you need to drilling machine (Important! Exact perpendicularity to the axial jig is ensured) drill two holes diametrically, stepping back 20-25 mm from the edge. It is necessary to drill through one side of the conductor and half of the second. One hole is working, the second is spare. In any case, you need to start and finish marking one traverse with only one and the same hole. When both conductors are ready, you can start marking the traverse itself. In this work, a tape measure is desirable, the length of which is greater than the size of the traverse. If you apply a tape measure several times when marking, errors in size are inevitable. Therefore, the markup must be done at a time. Before marking, I compile a table of distances from the zero mark in millimeters, that is, from the left end of the traverse. Point R (reflector) corresponds to the value "0" mm. When marking the traverse, two assistants are needed. The assistant on the left accurately fixes the "0" of the tape measure on the pipe cut. The assistant on the right provides the tension of the tape measure along the traverse. A sharply sharpened scriber on the pipe makes risks in accordance with the table. The risks, small but clear, must be applied exactly against the desired division and only once, across the pipe. After marking the traverse, conductors are put on its ends (Fig. 2). The right one is installed about a meter from the end and fixed with a stopper. And the left one is exactly flush with the cut pipe, and is also fixed with a stopper. Now, with a hand drill with a drill, which was used to drill the jig (2 or 2,5 mm) from above, using the SC as a guide, we drill through the traverse. Try to hold the drill more precisely vertically and do not press hard. First, the upper wall of the traverse is drilled, and then the lower one. The end of the drill hits the bottom of the diametrical hole. SK ensures that you drill exactly perpendicular to the axis of the traverse. Next, release the stopper of the left SC and move it to the right until the exact alignment of the left end of the SC with the next risk. We fix the conductor with a stopper and drill a second hole. This will ensure accurate positioning of the active vibrator. Again we unscrew the stopper of the left SC, and move it to the right until the left end is aligned with the next mark. So we sequentially move the left SC to the right to the middle of the traverse, without touching the right SC.
And now, when a hole for the fifth director (approximately) has been drilled, without releasing the stopper of the left SC (important!), unscrew the stopper of the right SC, remove it from the right end of the traverse, transfer it to the left end and secure it with a latch. T to the "field" where the conductors moved is even (we agreed in advance), then with further movement of the left SC to the right to the end and drilling for the rest of the directors, all holes are obtained exactly in the same plane and are perpendicular to the axial one. The second requirement is also met - all elements are strictly in the same plane. When the marking holes are drilled, remove the SC and drill holes for the diameter of the elements. When doing this work, be careful that a larger diameter drill does not “run away” to the side. It is better to work with a hand drill. Try to use a short drill. I made the reflector and director from aluminum wire with a diameter of 4 mm - from wires from 10 kV power lines. The rod turns out to be somewhat soft (it bends from crows and pigeons), but on the other hand, the antenna, even using a thin-walled steel pipe with a diameter of 22 mm (like mine), turns out to be very light. True, sometimes you have to climb onto the roof and straighten the elements with a long stick with a fork at the end. Because elements in the F9FT antenna pass through the traverse, I had to think about how to fix them there. I made the mount like this. From microporous rubber (a sealant for panels in the construction of houses), I cut columns 50 ... 60 mm long. To make it easier to push them into the pipe, I made them hexagonal, and in the middle applied an annular strip to them with white paint. Having cleaned the inside of the traverse from burrs (formed during drilling) and rust, one by one carefully drove the posts into the pipe. To do this, you need a "ramrod" with a length slightly more than half the length of the traverse. He took the traverse in his hands, carefully inserted a column of rubber and, running the pipe on the "ramrod", drove the column to the middle of the traverse. They are inserted into the holes for the elements, guided by the white annular strip. You need to be careful and not miss a single element, otherwise you will need to disassemble everything. Having thus filled one half of the pipe, turn it over with the other end and repeat everything. After installation, all the posts are drilled with a drill. I got 3 mm - it depends on the diameter of the elements, you need to experiment. For easier pulling of the elements through the traverse, they must be moistened with a damp cloth. Oil cannot be used - rubber corrodes over time, and the fasteners are not rigid. DJ9BV antenna elements are isolated from the traverse. I recommend using solid insulating sleeves. The fastening is more reliable if the sleeve is cut along. When pushing the cut sleeve through the traverse, it turns out, as it were, a collet clamp for the element. It is only necessary to more precisely select the diameter of the hole in the traverse. I made bushings from 8 mm vinyl tubes, and the holes in the traverse were 7 mm. A few words about attaching the traverse to the mast tube. It is best to fasten with U-shaped studs through a steel plate 4 ... 4,5 mm thick. For greater rigidity, it is better to bend the edges of the plate (top-bottom) at an angle of 90 ° by 4 ... 5 mm. And on the studs that fasten the plate to the mast pipe, under the nuts, you need to put strips-linings with a thickness of 5 ... 6 mm, so that when the nuts are tightened, the plate does not bend, i.e. so that the traverse remains straight. I do not advise drilling the traverse pipe for fastening, the wind will definitely break it in this place. Antenna mounting at 432 MHz must be done differently, because. when the mounting pipe-mast passes through the antenna sheet, the gain drops and the radiation pattern is distorted. My mount is made as shown in Fig.3.
A piece of pipe l = 1 m was taken, the diameter of which allows you to freely enter the rotary mast, and a platform is welded at one end. An antenna is attached to the site along the diameter of the traverse. To prevent the traverse from bending, it is supported from below by two struts made of pipes with a diameter of 14 ... 16 mm; The struts are fixed at the top with half-clamps on the traverse, and the lower ends are welded to a freely sliding machined ring with two M8 locking screws. This design makes it possible to accurately, without deflection, set the antenna traverse, no matter how long it is. After all the half-clamps are tightened, the antenna rises up, and with the help of a stick with a plug at the end it is inserted into the mast pipe. In parallel, the antenna is set to 144 MHz and tightened with locking bolts on the mast pipe. Author: G.Kamenev, Cherkessk; Publication: N. Bolshakov, rf.atnn.ru
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