|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Simple effective antennas for long-distance communications. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas The choice of antenna design is usually a difficult problem for every shortwaver, especially if he plans to work with distant stations and participate in prestigious international competitions. In this case, as a rule, preference is given to multi-element rotating antennas or antenna systems with a switchable direction of the main radiation. However, not all radio amateurs have a real opportunity to build such an antenna even for one band. Of course, not everyone is able to manufacture or purchase rotary devices, masts or trusses, a large number of structural materials. In addition, quite often the "antenna field" of an amateur radio station is limited to only a few square meters of the roof. It is no coincidence that many radio athletes, especially beginners, timidly join the competition, usually explaining this by the lack of complex antennas. In connection with the above, the author of these lines would like to acquaint readers with the results of many years of experiments conducted by the UZ3QBM team with the simplest types of antennas and their use in sports and everyday DX work. We fully agree with the master of sports V. Uzun (UB5MCI), who in his article "How to become a champion" (Radio, 1979, No. 3 and No. 4) wrote: "... The absence of multi-element rotating antennas on the radio station should not at all be a reason to withdraw from the competition. Indeed, having even simple, but high-quality and well-tuned antennas, clearly presenting their properties, objectively assessing the capabilities of the equipment and choosing the right tactics for the upcoming competitions, of course, you can achieve good results. They will undoubtedly grow with the accumulation of experience and the improvement of the entire complex of sports equipment. Let's assume, however, that your experience and technical capabilities are limited. Well, then the way out of the situation can be the construction of vertical whip antennas. Their designs with a radiator length equal to a quarter wavelength are described in detail in the literature. With an increase in size of more than half the wavelength, lobes appear in the radiation pattern in the vertical plane, directed at very small angles to the surface of the Earth. For a pin with a length of 5l/8, the radiation at small angles reaches a maximum. It was this property that was decided to be used in the antennas we create for high-frequency amateur KB bands. The system looks like this. The emitter with a length of 5l/8 is electrically extended by a series-connected inductance up to 3l/4, and the radial conductors (counterweights) have a length of l/4. Thus, from the emitter, inductance and balances, a kind of wave dipole turned out. Changing the resonant frequency and matching with the power line is achieved primarily by inductance, which is a critical element of the entire system. The table shows the dimensions of such antennas for the 14, 21 and 28 MHz bands. Table 1
In all varchants, the emitter is mounted on an insulator and is made with a decrease in diameter in the upper part. For the 10-meter band, it is made up of two parts, and for the 15- and 20-meter bands, respectively, of three and four duralumin pipes, fixed with the required number of stretch marks. The counterweights are made of an antenna cord and are connected to each other at the point between the pin and its base (one and a half meter pipe) isolated from them. At an angle within 95 ... 105 ° to the radiator, the counterweights descend to the roof. The antennas are powered by a coaxial cable with a wave impedance of 75 ohms of arbitrary length. A few technological tips for the manufacture of inductors. Since the coils are in the antinode of the current, they must be made in such a way that they retain their geometric dimensions when the signal changes. In antennas for the 21 and 28 MHz bands, the coils are made on frames made of insulating material, on which there is a groove with a given pitch. For a 14 MHz antenna, the coil is frameless. It is wound with a copper tube with a diameter of 4 mm on a mandrel with a diameter of 35 mm. After removing the mandrel, three plexiglass plates 5X12X100 mm in size are screwed onto the turns of the coil with holes 4,2 mm in diameter drilled into them with the desired pitch. These peculiar "stiffening ribs" are placed at an angle of 120 ° to each other. The tuning of the antennas was reduced to determining the resonant frequency and, if necessary, correcting it by changing the inductance of the coil. During this operation, a minimum SWR was achieved at the selected frequency. Well-tuned antennas have a wide bandwidth and are resistant to climate change and the underlying surface. Measurements showed that the SWR on the 14 MHz band did not exceed 1,4, on 21 MHz - 1,5, on 28 MHz - 1,8 (Fig. 1). The minimum values at resonant frequencies were respectively equal to 1; 1,02 and 1,08.
The performance of the whip antennas was evaluated by statistical method in comparison with various simple antennas for the respective bands. More than a thousand evaluation comparisons were made with contacts located from several hundred to several thousand kilometers. The most interesting are the data in relation to the quarter-wave pin. At a distance of up to 2000 km, the manufactured antennas "lost" it on the S scale up to 1,5 points. This is due to the fact that although their radiation patterns in the vertical plane have lobes at an angle of about 30 ", but the radiation intensity in this direction is less than that of traditional SRs. As the distance to the correspondent increases, the advantage of radiation at small angles begins to appear to the horizon and at a distance of 4000 ... 5000 km, a pin with a length of 5l / 8 "wins" an average of 1 point. On long routes, up to 10000 ... 2000 km, the signal level for both reception and transmission increases by 1,5 , 2 ... XNUMX points The advantage of the created antenna is most noticeable in communications along the so-called "long path" and on routes passing through the polar caps. Thus, despite the simplicity of design and low material costs, such systems show good results in amateur radio practice. It is pointless to dispute the advantages of multi-element antennas, but the years of use of whip antennas indicate that they allow you to quite successfully do both sports and DX work on the air. With external simplicity, these antennas occupy a certain space, which is very often limited. It is quite natural to want to somehow increase the coefficient of their use. However, the search for any compromise solutions can nullify all positive properties. Undoubtedly, any of the single-band antennas proposed above can be matched on all amateur bands, but such a task was not set, since the optimal result is not obtained on all bands. Therefore, dual-band options were tried, the idea of which was to connect a quarter-wave GP for a lower frequency range and a 5l / 8 pin length for a high frequency. So a 5l/8 long emitter for the 28 MHz band was used as an elongated quarter-wave pin at 14 MHz, for which the total number of balances was doubled, with half of them having a length of 2,62 m, and the rest - 5,3 m. the element is a relay that, on the 20-meter band, connects the central conductor of the feeder to a variable capacitor (100 pF), and on the 10-meter band, to the former inductor. Structurally, the capacitor is a piece of coaxial cable. Relay - RMug, the contacts of which are protected from moisture. An antenna for the 7 and 14 MHz bands is made according to the same scheme. However, here it was necessary to slightly reduce the length of the vertical part to 12,55 m so that the capacitance of the condenser included on the 40-meter band was not too small, as in the case of a radiator with a length of 13,2 m. In the final version, it was 180 pF. The total number of counterweights is eight, four 5,3 m long are evenly spaced in a circle, four more 10,8 m long are stretched taking into account the shape of the building. Otherwise, the design features of both dual-band antennas are the same as in the options described above. The appearance of switching elements should not cause any particular difficulties. To power the relay, a cable braid and an additional wire are used. In principle, it is possible to supply power through the central core, "untying" the high-frequency and constant components. In fig. 2 shows the dependence of SWR on frequency.
All the antennas discussed in the article were operated for several years both at the collective radio station and at the author's radio station. They were repeatedly repeated by radio amateurs. The antennas turned out to be quite technologically advanced, showed the stability of their parameters. Author: G. Bolotov (UA3QA) Voronezh; Publication: N. Bolshakov, rf.atnn.ru
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Silent power supplies Mean Well LSP-160 ▪ Genetic pacemaker powered by light ▪ Infineon launches 512Mb NAND storage ▪ Sleep patterns change significantly with age
▪ site section Spectacular tricks and their clues. Article selection ▪ article No great Patroclus! The scornful Thersites lives! Popular expression ▪ article How did the units of measurement come about? Detailed answer ▪ article Working with an endoscope. Standard instruction on labor protection ▪ article Double-chip filter for SSB. Encyclopedia of radio electronics and electrical engineering ▪ article Confetti from a magic wand. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua | |||||||||||||||||||||||||||||||||||||
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page