Designs of multi-element TV antennas wave channel. Single-band directional antennas 7 element antenna for 12 wave channel
Antenna material: square 25x25x1.5 mm, tube 8x1 for elements and 12x1 for split vibrator. Subsequently, during the manufacture of 14 element antennas, it turned out that it was preferable to use a 7x1 mm tube for the elements; it turned out to be more durable.
The material can be purchased in Khimki (see www.alros.ru with telephone numbers and directions) up to 6 meters long. In half (they cut 3 m for free, cut to size for little money). Please check stock availability before you go.
“Pilot MS” (north of Moscow, Lianozovo, website www.pilotms.ru) sells similar material, but 2 meters and, less often, 3 meters in length.
The design stipulates that the elements must be isolated from the boom and placed on top of it at a distance of 2-3 mm and fastened through special insulators, which cannot yet be found in our stores. Therefore, the fastening of the elements was carried out as follows:
50x40 mm plates were sawn from 3 mm thick fiberglass and pre-drilled holes with a diameter of 3.5 mm.
The plate is placed exactly in the center of the element and only one wall of the element is drilled through the hole in the plate with a 3.5 mm drill, a 3.2X8 blind rivet is inserted and riveted. 
The element is turned over on its back, the plate is aligned on the element, a second hole is drilled and riveted again. 
The element is placed on the boom in place, aligned in the center, first one hole is drilled and riveted. Then a right angle is established between the element and the boom and a second rivet is placed. 
This fastening allows you to very quickly replace elements in the event of a breakdown using old insulating pads.
And the last thing about hardware: if you plan to make several antennas at once, for example for a stack, do, if possible, the same operations from start to finish: cutting elements, making pads, attaching elements, etc. This order will increase the accuracy of production and identify mistakes.
And everything to the warehouse, until it warms up!!! 
Antennas for deuce - at the top, for 70 cm - at the bottom 
4x2 7 elements in KO86SH - on trial - June 2003
It would be better to make a 2x4 configuration, but in this case it would be necessary to significantly strengthen the last legs of the telescope... 
In KO71IM (PD 2003 team RW3WR) 
In KO71IM - a few hours before the fall…….
Nylon is a good thing, but insidious. After installation, you need to tighten the guy wires several times, and even if it rains... 
Transporting the “remains” to KO86SH…. 
4 x 7 elements in KO86sh in the “field” version - autumn 2003. The distance between the antennas is 2.5 meters. Neither the antennas, nor the vertical posts, nor the boom are stretched. It showed itself well in FD2004. 
Final stretch 2x2 with 14 elements - December 2003. The antenna withstood a wind of approx. 15 ms, although sometimes it seemed...
The “wave channel” antenna, known in the USSR, may have other names: director, Yagi And Uda-Yagi.
The last mysterious combinations of words are the names of two Japanese inventors who created this antenna in 1926.
As a rule, this is the main type of antennas that are currently used to receive television programs at a distance of up to 70 kilometers from the transmitter, both in the meter and decimeter wavelengths. The future lies in broadcasting in the decimeter range, where, in addition to the main programs, transmissions have been going on in digital format for several years now, and all programs that still occupy the meter range (50 -220 MHz) are already transmitted in the same mode.
The time has come for small-sized antennas in the range 480 - 800 MHz, because the higher the frequency, the shorter the wavelength and, therefore, the smaller the size of the structure itself, and there is no point in keeping bulky and expensive antennas on a pole.
Today, not all purchased antennas that look like a “wave channel” provide reliable reception in the decimeter range. To understand what was happening, I decided to make a homemade antenna from plastic, and for convenience, assemble it transformable, in order to see in practice how its elements affect the reception parameters.
To do this, I pull out into the white light from the last century a yellowed sheet from an old Soviet amateur radio manual, and begin to make a homemade antenna, which our fathers and grandfathers still made.
As a sample, I made a room or attic antenna, and, looking ahead, I will say that the number of elements with a margin was enough to receive multiplex packets without an amplifier at the level of the attic window of a wooden house, at a distance of 90 kilometers from Ostankino in the lowlands.
For antenna elements, I used metal plastic with a diameter of 16 mm, a material sold on construction markets. This is a high quality aluminum tube covered on all sides with plastic.
Antenna elements.
1. Active loop vibrator, its perimeter is equal to the wavelength, and the input impedance is 292 Ohms. The maximum operating frequency band is +/- 20 percent (for an average frequency of 600 MHz, the operating frequency band will be in the range 480 - 720 MHz).
2. Reflector. Modern antennas have several of them.
3.Directors. Their number generally reaches 12 for the most widely used antennas. It is believed that the more there are, the higher the antenna gain and the narrower the range. For a nine-director decimeter antenna from the reference book, the gain ranges from 11.5 to 8.5 dB, and its value decreases with increasing frequency. And in order to achieve a gain increase of 2 dB, the antenna arm with extended directors will have to be doubled. True, I have never seen such long antennas before.
Structural parts of the antenna.
4.Arm – part of the structure that serves to attach antenna elements. There are points of zero potential along the boom, so the material used does not affect the parameters of the antenna and can be made of metal or dielectric, for example, wood or plastic. If the antenna will be used outdoors on a mast, then the boom must be metal, and the point at which the middle of the vibrator is attached to the boom must have excellent electrical contact for further grounding of the antenna.
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| Director antenna. |
5. Brackets for fastening antenna elements.
6. Coaxial cable with a characteristic impedance of 75 Ohms, for example RG -59 or RK 75 - 3.7 - 35 M. At frequencies in the decimeter range, the quality of the reduction cable is important, since the longer the cable, the greater the losses in it.
7. Balancing-matching device, made in the form of a U-elbow from the same coaxial cable with a characteristic impedance of 75 Ohms. The length of this U-shaped cable is between 0.33 and 0.5 wavelengths. According to old reference data, this matching device provides matching of no more than +/- 20 percent of the center frequency, which will be a range of 480 - 720 MHz, and taking into account the loop matching range, the total maximum operating frequency band of the antenna will be 480 - 650 MHz.
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U-elbow is a balancing-matching device, the length of which is theoretically equal to half the wavelength. Taking into account the cable insulation material, a shortening factor is used, which for a coaxial cable made of foamed polyethylene is about Ku = 1.51 (indicated in the specifications for this cable). Therefore, the actual length of the U-bend will be 1.51 times less, which will be 0.33 wavelengths. During the adjustment process, by reducing the cable length, optimal matching is achieved for the minimum SWR in the frequency band. The initial length of the matching device is 250 mm. |
8. Insulating box.
Making an antenna.
The original dimensions are given in the figure. Apparently they are not very critical. When choosing a frequency, I took into account from the practical experience of making simple antennas made of metal plastic its characteristics that can move the frequency setting down by about 50 MHz and for convenience I chose a rounded calculated frequency of 600 MHz in order to tune the antenna to the range of Moscow multiplex packages 498 - 578 MHz.
Antenna test.
Autumn drizzle and fog - this is the joyful mood, the best time to test homemade antennas. The difficult testing conditions are complemented by a wet soft roof, tree foliage not shed by the cold, and low swampy terrain surrounded by forests in the Vladimir region, 90 kilometers from Ostankino. In the afternoon, to the sound of rain, sitting comfortably in the attic, I, like a boy installing ship masts on a caravel, assembled an antenna. I’m already clicking through analogue television channels in the UHF range, not bad for a homemade product (from “Pepper”, 487 MHz to “Friday”, 607 MHz, just excellent). It was for these frequencies that I planned to make an antenna.
Tuning in to one of the channels, I transform the antenna, leaving it without the outer director element. The image quality does not change.
I take out the second director element and notice the appearance of noise, which indicates a decrease in the antenna gain.
I remove the reflector, leaving one loop - very bad.
I return the director element to its place. The image quality is the same as with the reflector.
Conclusions.
The antenna has a limited gain range. The three-element antenna is quite sufficient for my reception conditions.
Now I connect the digital set-top box to the newly restored antenna. As expected, with a gain margin, 3 multiplex packages pass through. Again I pull out the director elements one by one and monitor the signal level as a percentage.
The last one has no effect on anything.
I pull out the second element, and the signal level has increased by a percentage!?....
And at this time, the “director” purchased antenna “Locus - Pro”, which in the guest house took only one of the three multiplex packages. I call my neighbor, who is 2 kilometers from me, he has a cool purchased antenna with three directories, and he says that digital broadcasting is not working now...
Conclusions.
To receive terrestrial digital television there is no need to use complex bulky antennas. The antenna itself does not require too high an installation height. It is not uncommon for failures in the reception of terrestrial digital television to occur due to a low-quality antenna amplifier. It would be more reliable to use several small-sized antennas without an amplifier for each TV, if any.
If we compare my homemade “wave channel” antennas with the 4-loop “Olympus 2014” antenna, then the rings are still in the lead, since they cover the entire decimeter range and have proven themselves well when working in bad weather conditions at extreme reception distances.
So why did highly directional antennas with high gain and excellent noise immunity behave inadequately in bad, rainy weather?
This phenomenon can be understood if we imagine the receiving antenna as a transmitting one. Then the antenna is a flashlight with a narrow focused beam, and the more directors in the antenna, the sharper its pattern and the better the focusing of the beam, and this focused beam simply rested on the wet tops of trees or on a rain cloud and dissolved there. With a wider radiation pattern, that is, with a lower antenna gain, when there are no director elements, the focus of the beam is more diffuse, but it covers a larger reception area, and the wide beam simply goes around the cloud in a circle, or passes between the wet treetops and the cloud.
Muscovites are always lucky, they have all the digital channels nearby! The “wave channel” antenna is suitable for them in a simplified form. Yes, any antenna will suit them! What should we do? We have a spacing between multiplex packages of more than 200 MHz! Stack antennas in shelves, where each floor works on its own range! It was these comments that I had already anticipated and even began to stack the antennas on whatnot. But what came of it, you will find out later. However, it’s already working out well.
Bread and circuses - this is what the Roman poet and satirist Juvenal said, and in some ways he was absolutely right. Modern society, and in particular modern people, can no longer do without pretentious pictures, shocking videos, exciting films, and comedy skits. One of these “elements” that can provide us with access to the world of entertainment is television. But even here it is not enough to have a TV, it also needs to have an antenna. After all, without a blooming antenna, radio waves are as difficult to catch as a fish on a hook without bait. What an antenna is needed for is not only prosaic to say, especially since we have already mentioned this in a utilitarian way, but more disrespectful to our reader. So, skipping the description of the antenna's purpose, let's proceed to the description of its creation. We wanted to talk about how to make an antenna with your own hands in this article.
Below we will present one of the simplest and, most importantly, affordable ways to make an indoor antenna for your TV. It is made utilitarianly out of nothing, or rather - 2 beer cans, self-tapping screws, a dress hanger, a wire and a plug.
DIY TV antenna made from beer cans
So, we need a couple of beer cans, a soldering iron, a TV cable, solder and a few other things. More on this in the course of our story.
Here you need to know in what order and what to do to get the much-desired television antenna. If we talk about the requirements for the materials used to make the antenna, then first of all, buy a good television cable. A good television cable requires a resistance of 75 ohms per meter, a strong central core and dense continuous double shielding. How much cable to buy depends on the location of the antenna, but know that the longer the cable, the more “useful” signal will be canceled out in it. (the rule clearly works for MV shafts). For UHF it also works, but is not so critical.
So, we make a cut for the plug and install it on the wire.
The plugs are now such that they don’t even require soldering, so everything will depend on the accuracy of your cuts and the size (diameter) of the cable. The photo shows a not very good option for installing a plug on the cable going to the antenna, try to do it better. In principle, a lot of detail about installing a plug on a television cable can be found in the article “How to insert a plug onto a cable to connect to a TV.”
Next, let's start working on the second TV cable cover. Here you need to bring out 2 cable conductors, one from the very edge, and the second after about 10-15 cm. The first conductor is considered the core, the second is shielding. Here you will also need to be careful not to cut through unnecessary layers of insulation and conductors. As a result, the efficiency of the antenna and the clarity of reception of television channels will depend on the quality of each and the total of all works - remember this. In the photo below you can see how the first and second conductors are removed from the cable. The top insulation is dropped to a distance of 10-15 cm from the edge of the cable.
Now about beer cans. We don't know what kind of beer you can afford and like, but cans are needed more. We repeat, not many, but big ones. 0.75 is good, but liter ones are even better. It’s hard to say anything about the 5 liter kegs of beer. This will probably go beyond the “framework” of an indoor antenna. After drinking beer, rinse the jars in water and dry them so that the aroma of the intoxicating drink does not change from them. Such a smell will not attract radio waves, but it certainly will attract flies.
Now we take the cable that we prepared earlier. Using small self-tapping screws, we fasten one conductor to the end of the first can, the other to the end of the second. To improve contact between the can body and the screw, use solder. Fill any possible gaps to improve contact.
Now our antenna is almost ready, we don’t have enough frame to base the cans together and to attach the antenna to something. In our case, the frame was a dress hanger. There are all criteria “FOR” for this. Low price, availability, proper rigidity and size. Yes, there is also a hook to hang everything at once in the chosen place.
So, we place the jars on one level surface, so that they are symmetrical relative to the center. “Play around” a little with the distance between them, since the quality of signal reception will depend on this. You can secure the cans with tape or tape. The standard distance for cans on the antenna is about 75 mm.
As a result, we get a not crafty, but functional thing - an indoor television antenna made from beer cans. Of course, such an antenna is only capable of operating in an area where a television signal can be reliably received. This is not an antenna for receiving a signal 20 km from the city, this is just something that will slightly make the reception more confident, but not ideal.
Professionals, perhaps, are already laughing sarcastically at this article and the antenna, because in fact, a television antenna requires a severe and precise calculation of its elements, depending on the received wavelength. In this they are absolutely right. But this calculation is not always accessible to the average person, which encourages him to undertake similar adventures in making antennas, such as in particular for the antenna shown here, from beer cans.
Next, we will consider a more serious option. First of all, its big advantage is that it will tell you how to make an antenna according to all the rules, taking into account the physiological characteristics of the propagation of radio waves.
Radio waves received by a TV antenna
Since we have climbed so far away, it is necessary to at least talk about the basics, because how could it be otherwise!? Radio waves of analogue television channels propagate in the range of meter (MV) and decimeter shafts (UHF).
In essence, this is the same thing, except that MV and UHF waves propagate at different radio wave frequencies. Meter shafts are from channels 1 to 21, and UHF from channels 21 to 40. It is important to note here that, depending on the wavelength, it will be necessary to use an appropriate antenna for VHF or UHF shafts. It is also necessary to say that antennas are available for both indoor and outdoor use. Let's consider one and the other option.
Do-it-yourself indoor TV antennas (MV and UHF)
MV indoor antenna
The strength of magnetic waves indoors is much less than outside. Therefore, it makes sense to use indoor antennas only in the immediate vicinity of the television center. So the simplest indoor antenna can be made from an electric wire or any other insulated conductor. An insulator is installed in the center of the antenna. Two guides are attached to it using fasteners (bolt - nut). The ends of the conductors are stretched so that they are even, like strings or rods.
The total length of the conductors of the two antenna frames is taken according to the wavelength and the received channel. These can be taken from the table.
If you choose the length of the antenna leads according to the television channel you are watching, then it will be much more effective than beer cans.
Next we will present another option for an indoor TV antenna that you can make yourself. This is a UHF antenna. Despite the fact that UHF channels are practically not used, broadcasting is still sometimes carried out somewhere. This means that we cannot ignore this topic either. Here is an example of a UHF antenna.
UHF indoor antenna
The mounting wire used, referred to as KPTA-1, serves to increase the antenna's noise immunity. To do this, as you can see, at a distance of 140 mm from the edge of the cable, the insulation was stripped to the screen and this mounting wire - a loop - was soldered. You can use another wire with a cross section of 0.35 mm.
The frequency of received radio waves from this antenna will be from 470 to 630 MHz, that is, UHF waves.
All antenna elements are mounted on a stand, which is a dielectric.
Do-it-yourself outdoor TV antennas (MV)
Antenna - half-wave linear vibrator
This outdoor antenna is designed to receive television waves near the city, 20-30 km away. In fact, this is an analogue of the simplest indoor antenna, which we already talked about a little earlier, except that it is adapted for the street.
So, as we have already learned, the antenna must have certain dimensions, which will affect the reception of television radio waves. The dimensions will depend on which channel you are going to watch. All dimensions for the antenna can be found in the table.
Rice. 1. Antenna - half-wave linear vibrator (Imagines a simple television antenna)
The input impedance of the linear vibrator (antenna) is 73 Ohms. The bandwidth of a linear vibrator depends on the outer diameter of its tubes and increases with increasing final diameter.
You should not choose D greater than 30 mm, since with its further increase the image quality does not noticeably improve, and the weight and dimensions of the antenna increase.
In table 1 shows the dimensions of the linear vibrator elements. The gap A between the ends of the tubes is equal to 50-70 mm.
The antenna is connected to a TV with an unbalanced 75-ohm input using a coaxial cable (RK-75-4-15, RK-75-9-12, etc.) The cable is connected to the antenna through a special balun (see Fig. 2 ).
The required dimensions of elements of matching structures are selected according to table. 2.
The antenna is made of steel, aluminum or brass tubes and metal strips. To attach antenna tubes to a metal or wooden mast, porcelain insulators and textolite are used.
An antenna - a half-wave vibrator is used in conditions of close enrollment, we have already talked about this. (20-30 km). This antenna option is, of course, a lot more labor-intensive than an indoor antenna, but its efficiency will be much higher. To receive television broadcasts far from the city, or rather from the transmitter, a “wave channel” antenna is used.
Do-it-yourself "wave channel" antenna for MV and UHF - calculation and diagram
At large distances from the transmitter, that is, the television center, this is about 40-90 km, antennas of the “wave channel” type are used. Such antennas have very good gain, but require strict directionality. If you use such an antenna in populated areas, this will reduce interference from adjacent sources, thereby improving the image.
The antenna “wave channel” in its structure consists of an active loop and linear vibrator. We talked about the linear vibrator in the previous paragraphs. The size of the antenna is selected based on the consideration of signal amplification; the farther it is, the more complex the antenna will be. Also, the number of directors can improve the receiving properties of the antenna by changing its sensitivity to the direction of the transmitter.
however, a large increase in the number of directors leads to a decrease in bandwidth. Here we need to find a “golden mean”. So on MV channels, 3, 5 and 7 element antennas are used.
The geometric dimensions of such antennas of the “wave channel” image are given in the table. At the same time, for channels 1-5, tubes measuring 18 mm are used in the design, and for channels 6-12, 12 mm.
| TV channel number | Dimensions in mm, for three-element "wave channel" antenna | |||||
| A | B | IN | A | b | V | |
| 1 | 2710 | 3040 | 2360 | 880 | 595 | 800 |
| 2 | 2300 | 2580 | 2000 | 750 | 505 | 800 |
| 3 | 1780 | 2000 | 1550 | 580 | 390 | 800 |
| 4 | 1620 | 1820 | 1410 | 530 | 355 | 800 |
| 5 | 1480 | 1660 | 1290 | 480 | 325 | 800 |
| 6 | 795 | 900 | 695 | 260 | 175 | 550 |
| 7 | 165 | 860 | 665 | 250 | 170 | 550 |
| 8 | 735 | 825 | 640 | 240 | 165 | 550 |
| 9 | 705 | 795 | 615 | 230 | 155 | 550 |
| 10 | 680 | 765 | 590 | 225 | 150 | 550 |
| 11 | 650 | 730 | 570 | 220 | 145 | 550 |
| 12 | 630 | 705 | 550 | 205 | 140 | 550 |
| TV channel number | Dimensions in mm, for a five-element "wave channel" antenna | |||||||||
| A | B | IN | G | D | A | b | V | G | d | |
| 1 | 2780 | 3150 | 2520 | 2510 | 2450 | 1210 | 735 | 705 | 750 | 800 |
| 2 | 2350 | 2660 | 2135 | 2125 | 2070 | 1040 | 625 | 595 | 630 | 800 |
| 3 | 1800 | 2035 | 1630 | 1620 | 1580 | 780 | 475 | 480 | 480 | 800 |
| 4 | 1620 | 1830 | 1470 | 1460 | 1420 | 700 | 425 | 430 | 430 | 800 |
| 5 | 1490 | 1680 | 1350 | 1340 | 1300 | 645 | 390 | 395 | 395 | 800 |
| 6 | 810 | 915 | 730 | 725 | 710 | 350 | 215 | 215 | 215 | 550 |
| 7 | 780 | 880 | 705 | 700 | 680 | 340 | 205 | 205 | 205 | 550 |
| 8 | 740 | 840 | 670 | 665 | 650 | 325 | 195 | 195 | 195 | 550 |
| 9 | 715 | 810 | 650 | 645 | 625 | 310 | 190 | 190 | 190 | 550 |
| 10 | 690 | 780 | 625 | 620 | 600 | 295 | 180 | 180 | 180 | 550 |
| 11 | 660 | 750 | 60 | 595 | 585 | 285 | 175 | 175 | 175 | 550 |
| 12 | 635 | 720 | 575 | 570 | 550 | 270 | 170 | 170 | 170 | 550 |
| TV channel number | Dimensions in mm, for seven-element "wave channel" antenna | ||||||||||||
| A | B | IN | G | D | E | AND | A | b | G | d | e | and | |
| 1 | 2760 | 3220 | 2200 | 2180 | 2160 | 2130 | 2105 | 1180 | 415 | 845 | 870 | 905 | 800 |
| 2 | 2340 | 2730 | 1870 | 1850 | 1830 | 1810 | 1790 | 910 | 350 | 715 | 735 | 765 | 800 |
| 3 | 1810 | 2120 | 1450 | 1430 | 1415 | 1400 | 1380 | 710 | 275 | 560 | 570 | 595 | 800 |
| 4 | 1650 | 1920 | 1320 | 1300 | 1290 | 1270 | 1260 | 645 | 250 | 505 | 520 | 540 | 800 |
| 5 | 1510 | 1760 | 1200 | 1190 | 1180 | 1160 | 1150 | 590 | 225 | 460 | 475 | 495 | 800 |
| 6 | 710 | 925 | 700 | 655 | 620 | 565 | 520 | 310 | 125 | 385 | 400 | 425 | 550 |
| 7 | 680 | 885 | 670 | 625 | 595 | 540 | 500 | 295 | 120 | 370 | 385 | 405 | 550 |
| 8 | 650 | 850 | 640 | 600 | 570 | 520 | 480 | 285 | 115 | 355 | 370 | 390 | 550 |
| 9 | 625 | 815 | 620 | 575 | 545 | 500 | 460 | 275 | 110 | 340 | 350 | 375 | 550 |
| 10 | 600 | 785 | 595 | 555 | 525 | 480 | 440 | 265 | 105 | 325 | 330 | 360 | 550 |
| 11 | 580 | 755 | 570 | 535 | 505 | 460 | 425 | 255 | 100 | 315 | 325 | 345 | 550 |
| 12 | 560 | 730 | 555 | 515 | 485 | 445 | 410 | 245 | 95 | 305 | 320 | 335 | 550 |
But for UHF shafts a 16 element antenna is used. The diameter of the tubes is 6-10 mm, and for the boom 14-16 mm.
For her, the dimensions are also shown in the table.
| TV channel number | Dimensions in mm, for an 11-element UHF wave channel antenna | ||||
| 21-25 | 26-30 | 31-35 | 36-40 | 21-40 | |
| A B IN G D E AND Z AND TO L A b V G d e and h And To l | 308 377 293 290 287 283 279 276 272 269 265 140 72 92 104 121 132 133 134 136 137 240 | 284 348 270 267 264 260 257 254 251 248 245 129 67 85 96 112 122 123 124 126 127 240 | 264 324 252 249 246 243 240 237 234 231 228 120 62 79 89 104 113 114 115 117 118 240 | 247 303 235 232 229 226 223 220 217 214 210 112 58 74 83 97 105 106 107 109 110 240 | 274 336 261 258 255 252 249 246 243 240 237 125 64 82 92 104 117 118 119 121 122 240 |
After the antenna is ready, you will need to extend the television, antenna cable from it to the TV. About this in the article “Connecting a TV to an antenna cable through a plug.”
Martin Steyer, DK7ZB, has prepared a very interesting overview of modern concepts and achievements of developers of such
antennas Using computer modeling, it is possible to accurately determine the dimensions of antennas, including Long Yagi antennas, which are designed for long-distance terrestrial and EME radio communications. True, Gunter Hoch, DL6WU, experimentally developed the design basis of an effective Long Yagi antenna 30 years ago. His development of this topic remains the "standard" for this type of antenna to this day. Before the appearance of Gunter's work, homogeneous antennas were common, in which the directors had the same length and equal distances between the elements. Such antennas were not optimal in terms of gain and had significant side lobes in the radiation pattern.
DL6WU found that gradually increasing the distance between directors to a maximum of 0.45X while simultaneously reducing their length leads to increased gain and improved radiation pattern antennas. In addition, he also determined correction factors for mounting elements on a conductive “boom”, established on the basis of labor-intensive experiments, which to this day cannot be simulated by computer programs available to radio amateurs. All calculation formulas use these correction factors.
To obtain the optimal compromise between gain, operating bandwidth and radiation pattern, Martin, DK7ZB, introduced a range of Long Yagi antennas in 1997 using the so-called. " 28 Ohm technique", and developed their theoretical foundations. Martin is constantly improving these antennas. Their characteristics are usually verified. The fact that these antennas are effective is evidenced by the results of many EMEs and contest groups using such antennas.
Another German radio amateur, Reiner Bertelsmeier, DJ9BV, found that not only the gain, but also the unwanted noise received by the side and back lobes of an antenna's radiation pattern plays a large role in assessing its effectiveness. He introduced the concept of the ratio of antenna gain (G) to noise temperature (T). This ratio is most often given on a logarithmic scale, i.e. in decibels.
There are two opposing approaches to solving the problem of antenna noise. In one case, antennas are designed for maximum gain, which leads, in particular, to their narrow bandwidth. The fact that these antennas, which necessarily have clearly defined side lobes of the radiation pattern, and the use of which does not pay attention to the G/T ratio, are effective in the 2-meter range, is confirmed by the high results achieved by some radio amateurs in EME radio communications.
The second approach involves significant suppression of side lobes in the radiation pattern, which, however, leads to a decrease in antenna gain.
Meanwhile, Lionel, VE7BQH, when evaluating the parameters of 2 meter antennas, considers two new values: the active impedance of the vibrator at a frequency of 144.1 MHz, as well as the SWR at a frequency of 145 MHz. The second value actually indicates the broadband of the antenna. In general, in Long Yagi antennas, the SWR graph is not uniform around a given frequency. The upper limit frequency is largely determined by the size of the directors. To obtain optimal antenna efficiency, the directors must be of a length that matches the desired operating frequency. Only at this frequency is maximum gain obtained.
SWR graph of 12-element antenna DK7ZB
12-element antenna DK7ZB
Figure 1 shows the SWR graph of the 12-element DK7ZB antenna (Figure 2) for the 2 m range. The calculated resonant frequency is 144.3 MHz, and above this frequency the SWR increases rapidly. You can expand the operating frequency band at the cost of reducing the efficiency of the directors, but then the gain at the operating frequency will decrease. The broadband of a Long Yagi antenna depends much more on the location of the directors than on the type of vibrator. The type of vibrator (simple dipole, complex dipole or loop) is of secondary importance.
From the point of view of amplification, antenna designers debate very intensively on the topic of a completely different parameter - radiation resistance, which depends on the distribution of currents in the vibrator and, most importantly, on the influence of neighboring passive elements. An additional role is played by ohmic losses as a result of the surface (skin) effect.
Basically, there are two methods for matching the supply cable (most often 50 ohms) with the antenna input impedance. Typically, Yagi antennas (both short and Long Yagi) with high gain and low operating bandwidth have a radiation resistance of less than 50 ohms. In short antennas, matching with a 50-ohm cable is achieved by installing an additional matching element very close to the vibrator. Such an element increases the radiation resistance. This is not a typical director, but rather an open-sleeve element that should be considered as a folded and compressed vibrator system. In this case, one must take into account the additional consumption of material, the weight of the antenna and the increased wind resistance of the structure. However, with thin VHF antenna elements, these considerations play a secondary role.
The second matching method implies that the antenna has a certain “native” resistance, which is reduced to a resistance of 50 Ohms by installing a transformer. With a carefully manufactured resistance transformation unit, the losses are no greater than in a “pure” 50-ohm system, which was confirmed by measurements on transforming wires on cables with low losses.
The goal of Ljubusa Rora's low-temperature Yagi design, YU7EF, is to significantly suppress the first sidelobe of the radiation pattern.
Horizontal radiation pattern of a 10-element Yagi 2m band
Figure 3 shows the horizontal radiation pattern of the YU7EF's 10-element 2m Yagi, which has a boom length of 5.3m and a gain of 12.57dBd. The strongly suppressed side lobe and the relatively weakly suppressed rear lobe are clearly visible.
While modeling a loop dipole as a dipole in Long Yagi antennas, Justin Johnson, GOKSC, noticed one phenomenon. In previous years, Yagi antennas predominantly used rectangular loop vibrators. They were placed vertically and were most often powered in the middle. Attempts to change this established structure brought virtually no benefit. However, G0KSC installed a rectangular loop vibrator in the horizontal plane between the reflector and the director (Fig. 4).
Rectangular loop vibrator in the horizontal plane between the reflector and the director
The antenna is fed in the middle of one of the sides of the vibrator (most often the rear), and has an input impedance of 50 Ohms. This device was subsequently called Loop-Fed-Yagi. With a slightly longer boom length compared to a traditional Yagi antenna, this excitation method results in greater broadband with slightly lower antenna gain.
New developments are currently emerging. Dragoslav Dobricic, YU1AW, paid attention to the design of the loop vibrator from G0KSC and once again modified the antenna power supply. The starting point for optimizing antenna parameters is the fact that the design and location of the vibrator (simple or loop) is a compromise between the need for maximum back-lobe suppression, maximum gain, and the required antenna input impedance. To solve this problem, YU7AW proposed a horizontal triple loop dipole (Fig. 5).
Horizontal triple loop dipole
One part of this dipole serves to reduce the distance to the 1st director and optimize this distance. The part of the loop dipole adjacent to the reflector can be used to optimize the suppression of the back lobe of the radiation pattern, and the middle branch of the dipole can be used to feed the antenna. The antenna input impedance can be made to 200 ohms, which provides very simple matching with 50 ohm coaxial cable.
The design of a triple loop vibrator is, of course, quite complex to implement, but the result is greater bandwidth than a traditional vibrator and better suppression of the rear lobes of the radiation pattern.
YU1AW claims that the triple loop vibrator can be installed on existing high-performance Yagi antennas and therefore significantly improve their performance (particularly back-lobe suppression). Unfortunately, at the time of preparation of this publication there is no information about the practical implementation of this idea.
Antennas of the "Wave Channel" type are widely used in various professional radio communication and radar devices. Most industrially manufactured collective and individual television antennas are also “Wave Channel” antennas.
This is due to the fact that such antennas are quite compact and provide high gain with relatively small dimensions. Sometimes the antenna, “Wave Channel,” especially in foreign literature, is called the Uda-Yagi antenna after the name of the Japanese inventors who first described it.
The "Wave Channel" antenna is a set of elements: an active vibrator and passive ones - a reflector and several directors installed on one common boom.
The operating principle of the antenna is as follows. A vibrator of a certain length, located in the electromagnetic field of the signal, resonates at the frequency of the signal, and an emf is induced in it. EMF is also induced in each of the passive elements, and they re-radiate secondary electromagnetic fields.
These secondary fields, in turn, induce additional EMF in the vibrator. The dimensions of the passive elements and their distances from the vibrator must be chosen such that the additional EMF induced in the vibrator by the secondary fields are in phase with the main EMF induced in it by the primary field.
Then all the EMF will add up arithmetically, ensuring an increase in the efficiency of the antenna compared to a single vibrator. To do this, the reflector is made slightly longer than the vibrator, and the directors are made shorter.
The symmetrical arrangement of the antenna elements relative to the direction of the transmitter creates conditions for the addition of the induced EMF in the vibrator only for the signal coming from the main direction. Signals arriving at an angle to the main direction create an EMF in the vibrator that is phase-shifted relative to the main direction, and therefore are added algebraically in the same way as vectors are added. Their vector sum is less than the arithmetic sum.
The signal coming from the rear direction creates induced EMFs in the vibrator that are antiphase to the main one, and they are subtracted. Thus, the directional property of the antenna is ensured, a narrow directional pattern is formed, which corresponds to an increase in the gain.
The elements of the “Wave Channel” antennas, which will be discussed below, are located horizontally in space, and such antennas are used to receive signals with horizontal polarization, when the electric field strength vector E is also horizontal. To receive signals with vertical polarization, the antenna must be rotated 90° so that its elements become vertical.
Due to the fact that the antenna elements are located at different points in space, the phases of the EMF induced in them by the primary field will depend on the coordinates of each element and their sizes, since its resonant frequency depends on the length of the element, and the phase of the induced EMF depends on the configuration of the element.
It should also be taken into account that the television signal occupies a relatively wide band of the frequency spectrum, and the properties of the antenna must be at least approximately the same for the entire frequency band of the received signal. Finally, for good matching of the antenna with the feeder, its input resistance must be purely active. From here it becomes clear how difficult it is to design wave channel antennas, especially with a large number of antenna elements.
Currently, many variants of such antennas have been developed with different numbers of directors of different sizes and with different distances between them. The process of designing a multi-element antenna of the “Wave Channel” type is not at all straightforward.
The designer may be given different tasks: either to achieve the maximum gain of the antenna, or the maximum protective coefficient of action, or the least unevenness of the gain in the received frequency band, or the minimum level of the side lobes of the radiation pattern or other factors.
In addition, during the design process, some antenna dimensions have to be specified, and the rest must be obtained as a result of calculation. This explains the fact that different literature sources give different sizes of antenna elements with the same number.
Unfortunately, in the literature, when describing antennas, there is no information about what initial data was used as the basis for the design of this particular antenna. It should also be taken into account that most of the variants of multi-element “Wave Channel” antennas were selected experimentally, which greatly complicates the repeatability of such designs.
The same is true in the manufacture of a multi-element "Wave Channel" antenna: even strict adherence to all its dimensions does not eliminate the need to perform careful instrument adjustments, since it is impossible to take into account variations in its design, such as non-parallelism of elements in the horizontal plane, twisting of the supporting boom, inevitable under load due to the fact that there is always an ellipticity of its cross-section that is not uniform along the length of the pipe, and twisting of the boom leads to the fact that the antenna elements are no longer in the same plane.
Local objects, metallic and non-metallic, nearby have a certain influence on the operation of the antenna, which cannot be taken into account. Finally, it is impossible to maintain all dimensions absolutely accurately; there will always be deviations within the tolerances, and with changes in the ambient temperature these deviations increase.
The antenna should be adjusted by changing the length of each element and the distances between them while controlling the shape of the radiation pattern, the value and nature of the antenna input impedance. Setting up requires special testing conditions that exclude the influence of local objects, and special instruments: a meter or decimeter wave generator of sufficiently high power, a field strength indicator, an antenna impedance meter. It is not always possible during the tuning process to simultaneously ensure that the input impedance of the antenna is purely active and has the desired value.
We have to put up with the resulting value of the antenna input impedance given its purely active nature. But in addition to adjusting the antenna, you also have to additionally adjust its coordination with the feeder. Multi-element “Wave Channel” antennas used in professional equipment are subject to mandatory individual configuration at the factory, and the equipment includes a device that allows you to adjust the alignment of the antenna with the feeder during operation.
Radio amateurs involved in the construction of multi-element antennas of the “Wave Channel” type, of course, do not have the opportunity to perform even an approximate adjustment of the antenna, and most of them believe that an antenna manufactured exactly according to the drawings should ensure normal operation. Unfortunately, the opposite is true.
The more elements an antenna contains, the more difficult it is to tune it and, on the other hand, the worse the actual characteristics of an untuned Antenna are. First of all, when an antenna is detuned, its radiation pattern suffers. It becomes asymmetrical, the maximum of its main lobe deviates from the antenna axis, and the side and rear lobes expand. Due to the fact that the ratio between the area of the main lobe and the area of the remaining lobes deteriorates, the antenna gain decreases.
The input impedance of the antenna acquires a significant reactive component, and its active component is very different from the nominal value that it should have according to the passport. As a result, the coordination of the antenna with the feeder is severely disrupted.
This results in a significant portion of the signal energy received by the antenna being reflected from the feeder and radiated back. into space without entering the input of the television receiver. Thus, all characteristics of the antenna, without exception, deteriorate sharply, just as a radio receiver with detuned circuits has neither the required sensitivity nor the required selectivity.
Sometimes such a receiver is not capable of receiving radio signals at all. All this explains the frequent disappointments of radio amateurs who, having built and installed a complex multi-element antenna of the “Wave Channel” type, are faced with the fact that they do not receive the expected results.
Practice shows that the antenna '' Wave channel”does not need to be configured and provides passport characteristics if it contains no more than three elements: a vibrator, a reflector and only one director. The gain of such an antenna is 6 dB, which is quite enough for its use in the short-range reception area. If such a gain turns out to be insufficient, radio amateurs are not recommended to build multi-element antennas of the “Wave Channel” type, but should give preference to antennas of other types that can provide high gains and do not require tuning.
It should be noted that there is one more problem associated with the use of multi-element antennas of the “Wave Channel” type. Typically these antennas contain a Pistolkors loop vibrator. The loop vibrator itself has an input impedance of about 300 Ohms and fits well with a coaxial cable feeder with a characteristic impedance of 75 Ohms by using a half-wave loop.
The loop reduces the input impedance by 4 times, from 300 to 75 Ohms, and provides balancing. When passive elements are added to the loop vibrator, the input impedance of the antenna is significantly reduced. Thus, the input impedance of a five-element antenna, depending on its size, can be in the range of 40...120 Ohms.
Being additionally reduced by 4 times by a half-wave loop, it drops to 10...30 Ohms, which leads to a sharp mismatch between the antenna and the feeder. Due to the reflection of a significant part of the energy of the received signal and its radiation back into space, the antenna gain is significantly reduced. In conditions of high field strength at a short distance from the transmitter, such loss of antenna gain is not dangerous: the main task remains protection from interference due to the narrow radiation pattern.
However, if a multi-element antenna was installed because a simpler antenna was not effective enough, this decision turns out to be erroneous.
The matter is complicated by the fact that in the literature, when describing multi-element wave channel antennas, the values of their input impedance are not indicated, since it very much depends on the antenna tuning. It is quite difficult to measure the input impedance of an antenna in amateur conditions, and without knowing it, it is impossible to correctly select the matching device circuit.
Three-element antenna Wave Channel
Two-element “Wave Channel” antennas are rarely used, since their characteristics are not much better than those of a single vibrator. Therefore, consider a three-element antenna, which is shown in Fig. 1. The antenna elements are made of a metal tube with a diameter of 12-20 mm.
Rice. 1. Three-element antenna “Wave channel”.
The mast and boom can be metal. In this case, the antenna elements must be reliably electrically connected to the boom by soldering or welding. If the boom is made of insulating material, there is no need to specially connect the antenna elements together. The location of the antenna elements corresponds to the horizontal polarization of the signal.
If it is necessary to receive a signal with vertical polarization, the antenna is rotated so that its elements take a vertical position. However, in this case, the upper part of the mast, approximately equal to the length of the reflector, must be made of insulating material.
The feeder is connected using a half-wave loop, as shown in Fig. 2. The input impedance of the recommended antenna sizes is approximately 150 ohms, so there is; mismatch between the antenna and the feeder. However, in conditions of close reception, it is more important that the directional pattern, narrowed in comparison with a single vibrator, weakens the reception of interference from other directions and reflected signals.
Rice. 2. Antenna - loop vibrator.
The dimensions of the antenna and the length of the unfolded loop are given in Table. 1.
Table 1. Dimensions of the three-element "Wave Channel" antenna, mm.
| Channel number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ! 8 | 9 | 10 | 11 | 12 |
| R | 3350 | 2840 | 2200 | 2000 | 1830 | 990 | 950 | 905 | 870 | 840 | 805 | 780 |
| IN | 2760 | 2340 | 1790 | 1620 | 1510 | 815 | 780 | 745 | 720 | 690 | 665 | 640 |
| D | 2340 | 2000 | 1550 | 1400 | 1290 | 690 | 660 | 630 | 610 | 585 | 560 | 545 |
| A | 900 | 760 | 590 | 535 | 490 | 270 | 255 | 240 | 230 | 225 | 220 | 215 |
| V | 600 | 510 | 395 | 355 | 330 | 180 | 170 | 160 | 155 | 150 | 145 | 140 |
| P | 1865 | 1581 | 1227 | 1116 | 1023 | 553 | 529 | 508 | 488 | 469 | 452 | 436 |
The gain of the three-element "Wave Channel" antenna of the specified dimensions is 5.1...5.b dB, which corresponds to an increase in the signal voltage at the antenna output by 1.8..1.9 times compared to a single half-wave vibrator. The opening angle of the main lobe of the half-power radiation pattern is 70°.
A three-element antenna installed on a mast 15...20 m high, in flat terrain, can provide normal reception of television broadcasts at a distance of up to 60 km from a 5 kW transmitter with a transmitting antenna height of 200 m.
Five-element antenna Wave Channel
In Fig. Figure 3 shows the five-element "Wave Channel" antenna. It differs from a three-element antenna by two additional directors and the sizes of the elements.
Rice. 3. Five-element antenna "Wave channel".
Due to the reduced input impedance of the antenna, which due to the inevitable detuning is impossible to even approximately indicate, the feeder should be connected to the antenna using a quarter-wave short-circuited loop shown in Fig. 4.
Fig: 4. Split half-wave vibrator.
The dimensions of this antenna are given in Table 2.
Table 2. Dimensions of the five-element "Wave Channel" antenna, mm.
| Channel number | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| R | 3130 | 2650 | 2060 | 1870 | 1710 | 840 | 840 | . 800 | 760 | 700 | 710 | 680 |
| IN | 2760 | 2340 | 1790 | 1620 | 1510 | 730 | 690 | 680 | 660 | 605, | 580 | 550 |
| D1 | 2510 | 2130 | 1650 | 1500 | 1370 | 720 | 680 | 660 | 640 | 610 | 580 | 560 |
| D 2 | 2490 | 2100 | 1630 | 1485 | 1360 | 720 | 680 | 660 | 610 | 610 | 580 | 560 |
| D3 | 2430 | 2060 | 1600 | 1450 | 1330 | 700 | 660 | 650 | 610 | 610 | 570 | 530 |
| A | 1200 | 1030 | 790 | 720 | 660 | 325 | 310 | 300 | 290 | 260 | 260 | 240 |
| V | 730 | 620 | 480 | 435 | 400 | 210 | 210 | 210 | 160 | 190 | 190 | 250 |
| c | 700 | 590 | 460 | 420 | 380 | 500 | 530 | 490 | 450 | 445 | 390 | 385 |
| d | 740 | 625 | 485 | 440 | 400 | 420 | 365 | 370 | 380 | 315 | 350 | 340 |
| Sh | 1418 | 1202 | 932 | 848 | 778 | 420 | 402 | 386 | 370 | 356 | 343 | 331 |
Gain five element antenna provided that it is precisely tuned for the specified dimensions, it is approximately 8.6...8.9 dB, which corresponds to an increase in the signal at the antenna output by 2.7...2.8 times compared to a single half-wave vibrator. The half-power beam angle is 50°. If the antenna has not been tuned, its parameters may be worse than those of a three-element antenna.
In addition to five-element ones, the sizes of seven-element, eleven-element “Wave Channel” antennas, as well as with an even larger number of elements, have been developed and some literary sources publish them. Such antennas are not considered here for the following reasons. As already noted, without careful tuning, such antennas, even those made exactly according to the drawings, have poor performance.
In addition, as the number of elements increases, the antenna bandwidth narrows. Thus, the bandwidth of a seven-element Wave Channel antenna is approximately 5% of the frequency to which it is tuned.
Therefore, when receiving a signal via the first frequency channel (average frequency 52.9 MHz), the antenna bandwidth will be only 2.65 MHz, i.e., significantly less than the frequency band occupied by the television signal spectrum, which is approximately equal to 7 MHz. Even on the fifth channel, the bandwidth of this antenna is insufficient.
And if in the range of 6-12 channels or in the decimeter range the bandwidth of a multi-element antenna turns out to be quite wide, due to the inevitable detuning, such home-made antennas turn out to be futile. Finally, in short-range conditions there is no need to install such complex antennas.
As for the far part of the line of sight zone or penumbra zone, it is necessary to use antennas with increased or greater
a gain that a detuned antenna cannot provide, and to obtain such a gain it is necessary to use an in-phase connection of several relatively simple antennas that do not need tuning and are well matched with the feeder.
Nikitin V.A., Sokolov B.B., Shcherbakov V.B. - 100 and one antenna designs.