Tri-band antenna. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
Comments on the article
Successful operation on the 14 and 21 MHz bands is difficult if the station does not have a directional rotating antenna. Very popular designs of such antennas are all kinds of "squares", but, as practice has shown, they do not have sufficient mechanical strength.
To a large extent, "wave channels" meet the necessary mechanical and electrical requirements. However, many radio amateurs do not dare to take on the construction of a multi-range antenna system of the "wave channel" type [1-4] because of the complexity of the design and the high consumption of materials.
As a result of calculations and experiments, the author of the article managed to create an easy-to-manufacture, compact, mechanically strong three-band antenna with good electrical parameters.
The basis of the antenna is a three-element "wave channel" for the range of 14 MHz, to the traverse of which four additional vertically mounted tubes are attached (Fig. 1). At their ends there are insulating pads through which the wire elements of the antennas for the 21 and 28 MHz bands are passed, which are at the same time braces of the antenna vibrators for the 20-meter range. In the horizontal plane, the antenna elements in the 14 MHz band are stretched with a nylon cable tied to the ends of the traverse. The ends of the antenna vibrators are attached to it for the ranges of 21 and 28 MHz. The lengths of the vibrators of the elements are given in table. 1. All active elements have an electrical break in the middle of the element.
Each antenna is fed by a separate coaxial cable with a characteristic impedance of 75 ohms through quarter-wave transformers.
A quarter-wave transformer is a line segment whose electrical length is 0,25l, and the wave impedance is defined as the geometric mean of the wave impedance of the power line and the antenna impedance, between which this segment is included. In our case, pieces of 50-ohm coaxial cable are used with a length of 351 cm (on the 14 MHz band), 234 cm (21 MHz) and 175 cm (28 MHz).
When balanced antennas are fed through an unbalanced line (coaxial cable), asymmetry currents occur, flowing through the cable sheath. This leads to the fact that the cable begins to radiate energy and, as a result, distorts and degrades the radiation pattern of the antenna. To combat this undesirable phenomenon, various balancing devices are used. The simplest for the 21 and 28 MHz ranges can be made from quarter-wave segments of a 50-ohm coaxial cable wound in the form of a single-layer coil at the ends of the tube in front of the vibrator feed point, and for the 14 MHz range directly on the traverse.
The described power system made it possible to obtain satisfactory agreement on all ranges. The minimum SWR value at resonant frequencies is 14,1; 21,15 and 28,35 MHz, respectively, equals 1,3; 1,5 and 1,4. For better matching, you will need to use gamma, omega or T-matchers.
The traverse is made of a thin-walled steel pipe with a diameter of 51 and a length of 6400 mm, to the ends of which are welded, continuing it, additional tubes with a diameter of 18 and a length of about 100 mm. They are tied with nylon stretch marks. The elements of the "wave channel" for the range of 14 MHz are made of duralumin pipes with a diameter of 30 mm. They are attached with four U-shaped clamps with a diameter of 6 mm to rectangular fiberglass pads with dimensions of 300X150X10 mm, and those, in turn, with two U-shaped clamps with a diameter of 10 mm, to the traverse.
Four vertical tubes with a diameter of 18 mm can be welded to the traverse or attached to rhombic platforms with a side of 150 mm and a thickness of 4 mm with two 6 mm Y-clamps. The platforms are mounted on the traverse using two U-shaped clamps with a diameter of 2 mm.
Antenna elements for the 21 and 28 MHz bands are made of copper wire with a diameter of 2 mm. They, as already noted, are passed through two holes in the insulating pads made of fiberglass with 100X60X5 mm exchanges, which are screwed with two screws to the ends of the vertical tubes. Guys are made of a kapron cable with a diameter of 7 mm.
The traverse is located at a height of 6,5 m from the ridge of the slate roof.
An antenna consisting of two three-element "wave channels" for the 21 and 28 MHz bands, where the elements of the 28 MHz antenna simultaneously act as guys for the antenna elements for the 21 MHz band, may be of some interest to radio amateurs. The geometric dimensions of the antenna elements are shown in Table. 2.
Literature
- Meshchevtsev B. Tri-band antenna - Radio, 1978, No. 1, p. 21
- Uzun V. Combined "wave channels" - Radio, 1979, No. 9, p. twenty.
- Gutkin E. Multi-band directional HF antenna. - Radio, 1985, No. 1, p. 21.
- Sepp K. "Wave channel" with two active elements. - Radio, 1988, No. 7, p. 17
Author: V. Gordienko (RB5IM) Donetsk; Publication: cxem.net
See other articles Section HF antennas.
Read and write useful comments on this article.
<< Back
Latest news of science and technology, new electronics:
Machine for thinning flowers in gardens
02.05.2024
In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers.
... >>
Advanced Infrared Microscope
02.05.2024
Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>
Air trap for insects
01.05.2024
Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>
| Random news from the Archive rose transistor
01.12.2015
A living organism, in which its own cell tissues are supplemented with artificial materials, which half consists of wires and microcircuits, is a common character in science fiction films and books. And despite advances in prosthetics, despite advances in neuroscience trying to bridge the gap between electronics and the brain, it still seems that such bionic beings, if they do occur, will be in the very distant future. However, researchers from the University of Linköping Magnus Berggren and colleagues report that they have managed to grow a cyborg rose that can change the color of the leaves with an electrical signal.
The initial idea that arose in Berggren's laboratory almost 15 years ago was to "eavesdrop" on the biochemical processes occurring in the plant and, if possible, learn to control them. Here, of course, we can recall genetic engineering, which allows you to interfere with the genetic program of the body, turn on or off certain genes, achieving the desired physiological effect at the right time. The successes of genetic engineering can hardly be overestimated, and they are especially great just with plants that are easier to work with and whose genome can withstand quite strong shakes. However, in Sweden, the prospects for genetically modified plants - if we talk about their practical application in agriculture - are much more modest than, for example, in the United States. So the researchers thought about what could be an alternative to genetic engineering methods, and as a result they decided to create not a genetically modified, but an electronic plant.
The task was to supply the plant organism with wires, so to speak, without surgery, so that they would form themselves right on the spot. To do this, it was necessary to find a polymer that would, firstly, be biocompatible, secondly, would dissolve in water, and thirdly, would allow recording what is happening inside the plant and sending signals inside it. From the solution, monomer molecules would rise through the plant vessels and polymerize in them, forming the very wires that would run through the entire plant, from roots to leaves. More than twelve organic substances were tried, but everything ended either with a blockage of the root system, or the molecules, once in the rose, were not assembled into conductive structures. In the end, the authors of the work settled on PEDOT-S:H, a water-soluble organic compound that is used in printed electronics.
Rising through the vascular system of the plant, the PEDOT-S:H molecules lost a hydrogen atom, and due to the released sulfur atom, they formed polymer chains 10 cm long. Using gold electrodes connected to a rose, it was possible to show that the plant works like a transistor, and that performance is quite comparable to that of a simple transistor assembled only from polymer molecules. In another experiment, the leaves of live, uncut roses were impregnated with a PEDOT solution with cellulose nanofibers using a vacuum setup - as a result, the researchers were able to change the color of the leaves (not the petals!) In the blue-green range by applying current of different voltages. (It is also worth emphasizing that here the organic electronics were formed not from the roots through the stem, but directly in the leaf.) The results of the experiments are published in Science Advances.
The designers of the "cyborg rose" themselves believe that their experiments will serve as the basis for further research, and that in the future, with the help of such organic wires, it will be possible to regulate the hormonal background in agricultural crops, stimulating growth, fertility, etc. Of course, one can ask a question how such an operation affects the plant itself, and whether it will die prematurely due to the presence of organic electronics in itself.
However, according to Magnus Berggren, the experimental plants with which they experimented with changing the color of the leaves are still alive, and the leaves are still with them. And yet, one cannot discount the opinion of skeptics who believe that we are “only” an outstanding work of art that has no practical prospects, and, one way or another, such electronic plants have yet to prove their advantages over genetically modified ones.
|
Other interesting news:
▪ Created a laser with a 67-attosecond pulse
▪ Biosensor for highly sensitive detection of molecules
▪ Intel Xeon Scalable Server Processors
▪ MIC28516/7 - 70V/8A Synchronous DC/DC Buck Converters
▪ A new method for searching for axions is proposed
News feed of science and technology, new electronics
Interesting materials of the Free Technical Library:
▪ section of the site Encyclopedia of radio electronics and electrical engineering. Article selection
▪ Siren article. Popular expression
▪ article What sad rhyme do English children tell a ladybug? Detailed answer
▪ Article Deputy director for production. Job description
▪ article Capacitance meter on a logic element. Encyclopedia of radio electronics and electrical engineering
▪ article Power supply and electric drive systems of modern camcorders - troubleshooting, repair. Encyclopedia of radio electronics and electrical engineering
Leave your comment on this article:
All languages of this page
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua
2000-2024
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese