|
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 Quantenna Square. Setup and design options. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas This article discusses practical issues of setting up and designing a square antenna. Setting At the very first stage of setup, it is necessary to symmetry and coordinate the feeder and the “square” vibrator. For two-element antennas with a distance between elements of 0.2L, when powered by a 75-ohm coaxial cable, the most popular is the use of a high-frequency transformer on a ferrite ring. Schemes and designs of such transformers have been repeatedly published in the literature. It should only be recalled that the transformers must have a sufficient gap between the turns of the wire (2-3 mm), insulated from the core, and be protected from moisture. For three- and four-element antennas with an input impedance of less than 50 ohms (that is, when the feeder resistance exceeds the input impedance), balancing and matching using a tuning line - a gamma matching device is most effective. Approximate initial data of such devices are given in table. 1. The diameter of the line wire can be taken the same as for the emitter frame (1,5-2,5 mm), the distance between the wires of the frame and the line is within 5-10 cm.
For each range, it is desirable to have a separate power cable with its own matching device, since various combinations, making it difficult to set up, do not allow you to get good matching on all ranges. To tune antennas, a radio amateur must have the following instruments: an SWR meter, a generator, a half-wave dipole, a short-wave receiver with a linear indicator of the received signal strength, an attenuator with a total attenuation of up to 50 dB and switching in steps of 3 dB. Antenna tuning must begin with determining the operating frequency of the system as a whole. To do this, connect a meter to the gap in the supply feeder and measure the SWR across the range every 50 kHz. Based on the measurement data, a graph is constructed and the tuning frequency is determined based on the minimum value. By changing the length of the vibrator, the minimum SWR is moved to a given frequency. For antennas with gamma matching devices, the frequency can be changed within ±30 kHz by changing the length of the matching line and the capacitance of the capacitor. Tuning to a given frequency can be done at a small height (1-2 m) from the ground (roof), taking a frequency correction (minus 75 kHz for 14 MHz and proportionally for other ranges). After this, raising the antenna to its working height, you need to check the SWR again for each band. When properly configured, the SWR should be around unity at the given center frequency of each band. At the edges of the range, it will increase, and the more elements the antenna has, the more: a two-element “square” in the 14 MHz range - up to 1,2-1,3, a three-element - up to 1,5-1,6, a four-element - up to 1,8 ,2-XNUMX. This is because as the number of elements increases, the system becomes more narrowband. Therefore, by the way, the optimal characteristics obtained at the operating frequency will deteriorate when detuned across the range. The latter circumstance is more significant than an increase in SWR, which only leads to an increase in power losses in the feeder, which have small values. After tuning the antenna to a given frequency, you can proceed to the second stage - tuning passive elements, that is, to obtain a radiation pattern. It should be noted that the quality of the antenna system depends on this work. Therefore, the radio amateur should not stop at the first satisfactory results and bring the tuning to the highest performance. This stage begins with adjusting the reflector to maximum suppress radiation back. To do this, at a distance of at least 2L at a height equal to the height of the center of the antenna, install a horizontal half-wave vibrator (with horizontal “square” polarization), to which a generator tuned to the operating frequency is connected. A receiver is connected to the “square” vibrator. Having pointed the “square” with the reflector at the generator, move the jumper of the short-circuited loop of the reflector, achieving the lowest signal value in the receiver. When tuning two-element antennas, then check the change in SWR over the range. Similarly, tune the antenna on other ranges, after which the reflector setting and the change in SWR are checked, starting from the first range. Such a series of successive adjustments must be performed until the changes in parameters during each adjustment exceed the measurement accuracy. In conclusion, the radiation pattern is taken and the ratio of radiation forward / backward at the operating frequencies of each range is determined. Finally, it is best to remove the diagram using the signals of radio stations located in two zones: near (up to 10-15 km) and far (800-2000 km). Three- and four-element antennas are configured in the same way. The director (directors) are adjusted according to the maximum signal on the receiver output indicator, turning the “square” to the generator. It should be kept in mind that the adjustment of the director(s) is not as dramatic as the adjustment of the reflector, and therefore requires more time and attention. To reduce time, it is useful to use a device for remotely moving jumpers of short-circuited loops, proposed by V. Begunov (UW3HY). see "Radio", 1975. No. 7, p. eleven. Inexperienced shortwavers, who are tuning directional antennas for the first time, should be warned against characterizing by signal estimates by other radio amateurs. The fact is that in such an assessment it is difficult to take into account the influence of a number of objective and subjective factors, which in the end can lead to erroneous conclusions. If it is decided to conduct an experiment, one must make sure that: the passage of the radio wave does not differ in any anomalous phenomena and at both points the same time of day (excluding twilight); the polarization of the antennas is the same; the correspondent has the ability to measure the signal on the linear section of his receiver and the output indicator, and the measurement technique does not differ from the generally accepted one; repeatable results are obtained. To eliminate at least some of the subjective causes, it is best to check the characteristics of the antenna in the receive mode in parallel. A similar technique can still be used to tune the simplest antenna - a two-element “square”. With this setting, statistical data is collected on measuring the forward/backward radiation ratio in the reception mode of various stations operating near the operating frequency, at different lengths of the short-circuited reflector loop, and its optimal length is determined. This method was tested at the UA3CT radio station and gave good results. However, to obtain reliable results, it was necessary to perform a large number of measurements at a distance to correspondents from 800 to 2000 km. Each point was plotted on the graph after averaging. Measurements were performed every 10 cm of the length of the reflector plume, and near the maximum value of the forward/backward radiation ratio - after 3-5 cm. For antennas with more than two elements, this method is not suitable, since it is impossible to catch signal changes from random stations when tuning the director. Variants of "squares" Here are some practical antenna schemes with short comments, providing a solution to design issues for radio amateurs themselves, depending on their capabilities. Since the two-element “square” is widespread and there are many publications on it (both in the USSR and abroad), we consider it inappropriate to present already known antenna options. We will limit ourselves to considering a two-element antenna at 14 MHz with active power supply to the reflector, which was first created by the authors, tested in 1968 at the UA3CT radio station and aroused the interest of many radio amateurs. The operating principle of this antenna is that the reflector supply current is phase shifted relative to the vibrator supply current by an angle at which nan is obtained. the greatest radiation of energy is towards the main direction and the least in the opposite direction. The antenna is shown schematically in the figure. The distance between elements is 0,2L. The reflector and vibrator are connected by a piece of coaxial cable, the length of which and antiphase inclusion in the frame provide the required phase shift. (The calculation of the phase-shifting line for an antenna with active power supply to the reflector is described in the article “Antenna with an active reflector” in the magazine “Radio”. 1968, No. 9. p. 17). The supply feeder is connected to the coaxial cable at a strictly calculated point.
To match the input impedances of the frames, gamma-matching devices installed in their lower corners were used. These devices have a somewhat unusual appearance. On both sides, two short-circuited loops 12-15 cm wide are connected to the frames. A wire is connected to the middle of the jumper of one of the reflector loops, which, passing through the insulating spacers parallel to the wires of the loop, through the capacitor C1 connects the jumper to the central residential coaxial line. In exactly the same way, but out of phase, a vibrator is connected. The antenna is tuned to the operating frequency by selecting the length of the vibrator loops, the minimum SWR is achieved using two gamma matching devices, and the maximum suppression of radiation back is achieved by selecting the length of the reflector loops and the length of the coaxial line. It should be noted that tuning such an antenna requires great skills, patience and time. After tuning the antenna, the following characteristics were obtained: gain -12 dB, forward/backward radiation ratio -30 dB, forward/side radiation ratio - more than 30 dB, rear lobe suppression - 20 dB below the main one, SWR at the operating frequency (14150 kHz) - 1,02. Among the three-element squares, the most successful design was created by the Soviet radio amateur A.F. Kamalyagin (UA4IF). The antenna is designed to operate on the 14 and 21 MHz bands. The design data of the antenna are given in table. 2. Its input impedance is about 50 Ohms on each range, so you can use a 50 Ohm cable as a feeder, connecting it to the frame directly or (better) through a balun transformer. You can also use a 75 ohm cable, but with a gamma matching device. There is a separate feeder for each range.
The antenna has the following design characteristics: gain relative to an isotropic radiator - 11,5 dB at 14 MHz and 12 dB at 21 MHz; forward/backward emission ratio - about 30 dB on both bands; front/side emission ratio - more than 35 dB on both bands; SWR at operating frequencies is about 1. The next antenna, which, in our opinion, deserves attention, is a three-element “square” for three bands, built by the American radio amateur WA7NFH. Its data are also given in table. 2. The input impedance of such an antenna on all bands is less than 50 Ohms, so it is advisable to use a gamma matching device. The author used a special transformer on a ferrite ring, which ensures matching of all ranges (SWR = 1) with one 50-ohm coaxial cable. The antenna has fairly good characteristics on the 21 and 28 MHz bands, satisfactory characteristics on the 14 MHz band and very compact dimensions (traverse length is only 4,88 m). The parameters of the WA7NFH antenna, determined by calculation, at 14, 21 and 28 MHz, respectively, are as follows: gain relative to an isotropic radiator - 10, 11,5 and 12 dB, forward/backward radiation ratio - 27, 30 and 28 dB. The last three-element square antenna we think should be shown (as a negative example) is the 14 and 21 MHz three-element square built by Canadian ham VE7DG (see Table 2). The author of the antenna swapped the places of the reflectors and directors, so on the 14 MHz range the forward/backward radiation ratio is only 15 dB. at 21 MHz-25 dB. Of the four-element square-type antenna systems, the most popular is the WOAIW antenna with the same distance between elements (3,05 m), designed to operate at 14, 21 and 28 MHz (see Table 3). Its input impedance on the 14 and 21 MHz ranges is about 50, on the 28 MHz range it is about 40 Ohms. The author suggests directly connecting a 50-ohm cable at 14 and 21 MHz, and at 28 MHz through a 175 cm long piece of 75-ohm coaxial cable.
The antenna has optimal characteristics at 21, good at 28 and satisfactory at 14 MHz. However, these "satisfactory" characteristics are comparable to the optimal characteristics of a three-element "square". This, as well as a very simple symmetrical design, are obviously the reasons for the great popularity of the W0AIW antenna among radio amateurs. Another potential feature of this antenna should be noted: it can accommodate a two-element “square” at 7 MHz with a distance between elements of 0,2L. The list of options for "squares" could be continued (designs of five- and six-element antennas have been developed), but it seems to us that this is not necessary, since the main conclusions and recommendations that the authors came to as a result of experiments and calculations are quite well illustrated. Literature
Publication: cxem.net
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Coffee reduces the risk of liver disease ▪ Melting glaciers in the Swiss Alps recognized as unprecedented ▪ Emergency power supply of the LED lamp up to 3 hours ▪ Garmin Quantix 5 marine smart watch
▪ section of the Electrician website. PUE. Article selection ▪ article Organic synthesis. History and essence of scientific discovery ▪ article Assembler of products and structures. Job description ▪ article Directly opposite orders. 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