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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Five-element YAGI at 20 meters. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas Making an antenna yourself is not an easy task for radio amateurs. Often, the authors of various antennas do not pay attention to the description of the antenna manufacturing technology, and this is very important for those who will try to repeat them. Without knowing the manufacturing technology, it is difficult to fully assess their own capabilities. Their overestimation often leads to the fact that good designs, despite the materials already spent, remain unfinished. The proposed article describes in detail the design of the antenna for a range of 20 meters. Some manufacturing techniques can help in the manufacture of antennas of other bands. The problem of choosing an antenna was faced by the team of the Inta Radio Club (RK9XXS) at the very beginning of its activity. Even then it was decided: to make only serious antennas. Realizing well that you can’t make an antenna quickly, we decided to first collect materials, and based on their quantity, decide which antenna to build. Within a month, we managed to find 10 duralumin bars for high jumps 3,6 m long, 10 pieces of a 30 mm pipe 1,5 m long, two pipes from a medical stretcher with a diameter of 36 mm, two six-meter duralumin pipes with a diameter of 60 and 70 mm and one three-meter pipe with a diameter of 60 mm. This material was enough to build a 5-element YAGI antenna. Having experience in calculating antenna systems using a computer and manufacturing calculated antennas, we began the preliminary design of the antenna. The very first estimates showed that it is most profitable to build an antenna on an elongated traverse: the gain is higher, the front / rear ratio is better. The main requirement for a club antenna, in our opinion, is the ability to operate with a minimum SWR in the frequency band 14 ... 14,35 MHz. This is due, first of all, to the diverse interests of the club members: one loves the telegraph section, the other loves SSTV, the third is a fan of island expeditions, the fourth loves the MT-63. When the antenna was subsequently modeled with maximum gain in the direction of the main lobe, it turned out that our antenna loses only 0,5 ... 0,7 dB. This suited us just fine. The calculations were carried out with the YAGIOPTIMIZER program, and checked with the NEC4WIN95 program. In fairness, it should be noted that both programs are very close in terms of the final result, although there are some discrepancies. Dimensions of antenna elements: reflector - 10,7 m, vibrator - 10,3 m; director 1 - 9,88 m, director 2 - 9,58 m; director 3 - 8,9 m. Antenna characteristics: gain - 11,6 dB; front/rear ratio - 24 dB; front / side ratio - 35 dB, input impedance - 50 ohms. So, the main dimensions were determined, it's time for technological solutions. The antenna manufacturing technology was chosen in such a way as to minimize the amount of "paid" work and the main part of the details could be done independently using a simple tool. For the work, an electric drill, metal shears, a hacksaw, hammers, pliers, taps, dies, wrenches, screwdrivers and other little things were needed. There is not much welding work - only six simple knots. Turning works - 10 duralumin bushings. Everything else is done independently, without the use of special equipment. The issue with the traverse was most simply solved: a pipe with a diameter of 70 mm was placed in the middle, pipes with a diameter of 60 mm were inserted into it from both sides. The gap between the pipes was eliminated with a strip of steel tape 1,5 mm thick, tightly wrapping thin pipes with it. The joints were fixed from turning with M 10x80 bolts. At a distance of 1500 mm from the ends, two holes were drilled and fixed with M 10x100 bolts, two steel loops with dimensions of 30x120x5 mm for attaching the top and side braces (Fig. 1).
At the marked places, the attachment points of the elements were installed (Fig. 2). These platforms completely isolate the elements from the traverse with a minimum capacitance between them. Element fastening platforms consist of a steel plate 3 mm thick and a textolite plate 100x250x15 mm in size. 16 coaxial holes with a diameter of 6 mm were drilled in the steel and textolite plates, after which eight holes were drilled in the steel plate to a diameter of 25 mm. This is necessary so that the ladders for fastening the elements do not have contact with the steel plate. Then, four more holes with a diameter of 8 mm were drilled in the steel plate for attaching the platform to the traverse, and a pipe with a diameter of 17 mm and a length of 500 mm was welded for the upper braces of the element (stand). The plates are fastened together through undrilled holes with eight M6x25 bolts.
Step-ladders are made of unannealed steel bar with a diameter of 8 mm. To fasten the elements, ladders with a diameter of 6 mm were made (construction nails were used). First you need to cut the bar of the desired length, then cut the threads at the ends to a length of 30 mm, and then bend the ladder on the anvil to the desired shape. It is easy to calculate the length of the bar using the formula L \u1,57d 2 * (D + d) + D + 40 * M + XNUMX, where L is the required length of the rod; D is the diameter of the pipe that the ladder is attached to; d is the diameter of the bar from which the ladder is made; M is the thickness of the part to which the pipe is attached; 40 mm - stock for fastening nuts. A simple way to bend a ladder is shown in fig. 3. In the process of bending, one hammer is pointed at the stepladder; the second one is applied with light blows. The ladder profile is controlled by a template or a fixed pipe.
The antenna elements (Fig. 4) are made up of a 36 mm pipe segment (in the center), two high jump bars and two 30 mm pipe segments (at the ends). The jump bars are tightly inserted into the tube with a diameter of 36 mm and fixed with standard clamps, and the tube sections are joined to the bar with specially machined duralumin bushings and rivets made of aluminum wire with a diameter of 5 mm. At the junction, a loop is installed for attaching the upper and outer stretch marks of the elements. The loop is made of a rod with a diameter of 6 and a length of 90 mm (building nails can be used). A M20x6 thread is cut from one end to a length of 1 mm, the other end is bent into a ring on a mandrel with a diameter of 15 mm.
The traverse fastening unit (Fig. 5) assumes the main load of a static and dynamic nature and must provide high strength. It is a 4 mm thick steel plate. The size of the plate is determined by the length of the traverse and the weight of the antenna, the minimum dimension "B" for this antenna is 500 mm. Holes are drilled in the plate for clamps for attaching the traverse and for clamps for attaching the plate to the mast.
Hole marking is done as follows. Distance "A" should be equal to the sum of the diameters of the mast and the ladders that fasten the plate to the mast. In our case, the diameter of the mast is 52 mm, and the ladders are made of a bar with a diameter of 8 mm, so the distance between the centers of the holes is 60 mm. Distance "B" should be equal to the sum of the diameters of the traverse and the ladders that fasten the traverse to the plate. In our case, the diameter of the traverse is 70 mm, and the diameter of the bar from which the ladders are made is 8 mm. The distance between the centers of the holes is 78 mm. The number of traverse mounting ladders for such a heavy antenna is at least 6. This determines the reliability of the traverse mounting. The number of ladders for attaching the plate to the mast for long antennas should be 6-8. It determines the holding strength of the traverse on the mast. We chose six ladders. After marking and drilling these holes, a hole was made in the lower corner for the side bracing bracket. The diameter of this hole must be equal to the diameter of the pipe selected for the bracket. Bracket tube is 1,5" diameter, i.e. 37 mm. We chose the length of the bracket pipe (dimension "D") approximately 1000 mm. Two holes 12 mm in diameter were drilled in the bracket pipe at the ends, into which the tension bolts of the side braces will be inserted. The bracket tube is inserted into a hole in the steel plate so that the length of the ends is the same. After that, the pipe must be carefully welded by arc welding on both sides. The mount is carefully sanded and painted with outdoor oil paint. The tension bolts of the top and side braces are made of a steel bar with a diameter of 12 mm and have a length of 250 mm. One end of the rod is bent into a ring on a mandrel with a diameter of 15 mm, at the other end, a M12x1,5 thread is cut for the entire remaining length. The side and top braces of the traverse are best made during the antenna assembly process, since their length is determined by the center of gravity of the antenna system. Attachment of traverse braces is shown in fig. 6.
Antenna assembly. First, the antenna traverse is assembled, as indicated above. The traverse is laid on a clean, flat horizontal platform measuring 12x16 m. On the traverse, with the help of stepladders, the mounting areas of the elements are installed, and on them (also with the help of stepladders) - the assembled antenna elements. In this case, you need to pay attention to the horizontality of all elements of the antenna. The distance between elements is shown in the table.
When installing the elements, the fastening loops of the upper and outer braces must be on top. The top view of the antenna is shown in fig. 7.
Then, the upper stretch marks of the elements are marked and insulators are installed on them. The more insulators are installed, the less influence on the parameters of the antenna will be exerted by the upper extensions. In the case of using dielectric (nylon, hemp) upper stretch marks, insulators can be omitted. Stretch marks are attached at one end to the loops on the elements, with the other end to the supporting posts, passing the stretch marks into the holes drilled in the posts (Fig. 8).
For all attachment points of stretch marks, thimbles must be used. External stretch marks are attached to the loops on the elements. It is advisable to wrap these stretch marks in the attachment points with strips of galvanized sheet, then they will last a long time. External stretch marks should be as tight as possible, but evenly stretched. The most important thing is to ensure the correct position of the antenna elements. Our design used steel cables for the top guy lines and hemp cord for the outside guys. After attaching all the stretch marks, a matching device is installed (Fig. 9). It is attached with clamps or stepladders. The power cable is connected, fixed and laid to the center of the mast immediately. The body of the matching device must protect the capacitors from rain and snow.
Now the antenna is assembled and you can determine its center of gravity. To do this, raise the traverse between the first and second directors and, moving the fulcrum, find the equilibrium position of the antenna. In this place, the center of the traverse attachment point is installed so that the bracket of the side braces is at the bottom. Mounting of the traverse on the mast is shown in fig. 10.
After that, measure the distance between the holes of the bracket and the steel loops on the traverse. According to these dimensions, side extensions are made, making a margin for tension. Before lifting the antenna, be sure to check all fasteners, tighten all nuts. Supporting the traverse in two places, raise the assembled antenna to the UNZHI machine. on which the gearbox with the carrier pipe is fixed. Having pressed the attachment point to the carrier pipe, fix it with the help of stepladders. Having leveled the traverse with the help of supports, measure the distance between the upper part of the carrier pipe and the fastening loops of the upper braces. According to these dimensions, upper extensions are made and installed. Immediately it is necessary to ensure the tension of the upper and lateral extensions of the traverse, controlling the absence of vertical and lateral deflection. This is the only assembly work carried out at a height of 3 m. Now the antenna is fully assembled and, having raised the sections to a height at which it is still possible to work with the matching device, the omega-matcher is adjusted. Setting. Two antennas built according to computer calculations required only the adjustment of the matching device. There were no lengthening or shortening of the elements and their movement on the traverse during the tuning process. The setting of the matching device is reduced to setting the capacitor sliders to the position corresponding to the maximum power output with a minimum SWR in the middle of the range. In the case of establishing a matching device at a height of 3 ... 4 m from the ground, tuning is carried out at a frequency of 14100 kHz, while it is necessary to check the SWR at frequencies of 14 and 14,35 MHz, where it should not exceed 1,1. A tuned antenna should have an SWR of no more than 1,1 over the entire range of 20 meters. Yu. Pogreban (UA9XEX), A. Kishchin (UA9XJK), A. Kolpakov (UA9XKT), A. Bogomolov (UA9XBL), M. Gribak (UA9XEQ) took part in the design and construction of the antenna. General designer and construction superintendent N. Filenko (UA9XBI). Author: N.Filenko (UA9XBI)
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