HF antenna is a Square. Setting and design options
This article discusses the practical issues of setting and design of the antenna "square".
In the first configuration phase, symmetrical and agree a vibrator feeder and "square".
For two-element antennas with spacing between elements 0.2 L when the power is 75 Ohm coaxial cable is the most popular application of high-frequency transformer on a ferrite ring. The scheme and design of such transformers have been widely published in the literature. It should be noted that the transformers must have sufficient clearance between the turns of wire (2-3 mm), isolated from the core, and to be protected from moisture.
For three and up antenna with an input impedance less than 50 Ohms (that is, when the resistance of the feeder exceeds input impedance) most effectively balancing and harmonizing with the use of configurable line - gamma-matching device. The approximate initial data such devices are shown in table. 1. The diameter of the wire line can be taken the same as for the frame of the radiator (1.5-2.5 mm), the distance between the wires of the frame and line - in the range of 5-10 cm.
For each range, it is desirable to have a separate power cable with a matching unit, as different combinations, making it more difficult setting, do not allow to obtain good agreement at all ranges.
To configure the antennas ham radio operator must have the following devices: SWR meter, generator, half-wave dipole, a shortwave receiver with a linear indicator of the strength of the received signal, the attenuator General attenuation to 50 dB and switching through the steps of 3 dB.
The antenna setup should begin with determining the operating frequency of the overall system. For this gap in the supply feeder include a meter and measure the SWR on the range every 50 kHz. By measuring the build schedule and the minimum value determines the tuning frequency. By changing the length of the vibrator moves the minimum SWR at the desired frequency. For antennas having a gamma matching device, you can change the frequency within ±30 kHz by changing the length of the matching line and the capacitance of the capacitor. Tuning to a predetermined frequency can be performed at a low height (1-2 m) from the ground (roof), taking the amendment in frequency (minus 75 kHz to 14 MHz and in proportion for other ranges). Then, holding up the antenna to the working height, it is necessary to check the SWR on each band. When properly configured, the CWS should be near the unit at a given average frequency of each band. On the edges of the range would increase, and the more elements has antenna: dual-element of the "square" in the range of 14 MHz to 1.2-1.3, a three - to 1.5-1.6, the up - to 1.8-2. This is because as we increase the number of elements of the system becomes more narrowband. Therefore, the optimal parameters obtained at the operating frequency, will be negatively affected by the detuning range. The latter circumstance is significantly more than the increase in the CWS, which leads to increased power losses in the feeder, having a small size.
After setting up the antenna at a given frequency, you can proceed to the second stage - setting up of passive elements, that is to receive the pattern. It should be noted that this work depends on the quality of the antenna system. Therefore, a radio Amateur must not stop on the first satisfactory results and to bring the setting to get higher performance.
This phase starts with the configuration of the reflector by the maximum radiation suppression ago. To do this, at least 2L at a height equal to the height of the center of the antenna, set the horizontal half-wave vibrator (horizontal polarization "square") which is connected to the oscillator, tuned to the operating frequency. The vibrator of the "square" plug in the receiver. Sending a "square" reflector on the generator, move the jumper shorted loop reflector, achieving the lowest value of the signal at the receiver.
When you configure two-element antennas then check the SWR by changing the range. Similarly, adjust the antenna on other bands, then check the setting of the reflector and the SWR change, starting from the first range. This series of adjustments should be performed while changing the parameters at each adjustment exceeds the measurement accuracy.
In conclusion, remove the pattern and determine the ratio of the radiation forward/backward at the operating frequencies of each band. Finally figure it is best to remove the radio signals in two areas: near (10-15 km) and long (800 - 2000 km).
In the same way set up three-and up to the antenna. Director (Directors) adjust for maximum signal on the indicator of the receiver output, expanding the "square" on the generator. It should be borne in mind that the setting of the Director (Directors) are not as pronounced as the setting of the reflector, therefore, requires more time and attention.
To reduce the time that it is useful to use the device for remote travel jumpers shorted loops, proposed by V. Begunov (UW3HY). see "Radio", 1975. No. 7, p.11.
You should warn the inexperienced Amateurs who setup directional antennas for the first time, from the definition of the characteristics of the estimated signal other hams. The fact that such an assessment is difficult to account for the influence of a number of objective and subjective factors, which ultimately can lead to erroneous conclusions. If, however, decided to conduct an experiment, you should make sure that: the passage of radioval doesn't have any anomalous phenomena and in both points one and the same time of day (excluding twilight); the polarization of the antennas are the same; the reporter has the ability to measure the signal in the linear range of its receiver and indicator output, and the measurement technique does not differ from generally accepted; received repeatable results.
To exclude at least some subjective reasons, preferably in parallel, to test the performance of the antenna in receive mode.
This technique can be used to set up the simplest antenna - dual-element "square". In this configuration, gain statistics on the measurement of the ratio of radiation forward/backward in receiving various stations operating near the operating frequency, at various lengths of short-circuited loop reflector and determine the optimal length. On the radio UA3CT this method was tested and gave good results. However, to obtain reliable results had to perform a large "number of measurements at a distance of correspondents from 800 to 2000 km Each point was plotted on a graph after averaging. Measurements were performed every 10 cm of length of the loop reflector, and close to the maximum value of the ratio of radiation forward/backward through 3-5 cm.
For antennas having more than two elements, this method is unsuitable, so as to catch the change of the signal on a random stations when tuning Director's impossible.
Here are a few practical circuits of antennas, providing a solution of design issues by radio Amateurs and their capabilities.
Because of the two-part "square" is widely distributed and there are many publications (both in the USSR and abroad), we consider it inappropriate to give known antenna options. Consider a two-element antenna for 14 MHz active power to the reflector, which was first created by the authors, tested in 1968 at the radio station UA3CT and has attracted interest from many hams. The principle of operation of this antenna is that the supply current of the reflector is shifted in phase relative to the current power of the vibrator on the angle at which it turns out Nan. greater energy radiation in the direction of the main direction and the lowest in the opposite direction.
The antenna is shown schematically in the figure. The distance between the elements is equal to 0.2 L. the Reflector and a vibrator connected piece of the coaxial cable, whose length and inclusion in antiphase framework provides the desired phase shift. (Calculation of phase-shifting lines for antennas with active power to the reflector from the article "active Antenna with reflector" in the magazine "Radio". 1968, No. 9. p. 17). To coaxial cable in a carefully calculated point connected to the supply feeder.
To align with the input impedance of the framework used gamma matching device installed in their lower corners. These devices have a somewhat unusual appearance. With both of the parties to the framework are connected by two short-circuited loop width of 12-15 cm To the middle of the lintel of one of the loops of the reflector attached wire, which, passing through the insulating spacers parallel to the wires of the cable, through the capacitor C1 connects the jumper from the Central core of the coaxial line. In the same way, but opposite phase, connected to the vibrator.
At an operating frequency of the antenna set selection of the length of the ribbon vibrator, minimum SWR achieve with the help of two gamma-matching devices, and the maximum suppress radiation back - selection of the length of the loops of the reflector and the length of the coaxial line. It should be noted that the configuration of this antenna requires great skill, patience and time.
After setting up the antenna yielded the following characteristics: gain-12 dB, the ratio of the radiation forward/backward-30 dB, relations radiations forward/sideways - more than 30 dB, the back lobe suppression 20 dB below the main, the SWR at the operating frequency (14150 kHz) - 1,02.
Among three of the squares of the most successful design, created by Soviet radio A. F. Kamalapuram (UA4IF). The antenna is designed to operate on the bands 14 and 21 MHz. Structural data of the antenna are shown in table. 2. Its input impedance is about 50 Ohms on each band, so as feeder, you can use 50 Ohm cable by connecting it directly to the frame or (better) via a balun transformer. You can use 75 Ohm cable, but with a gamma matching device. Feeder to separate each range.
The author designs
Frame length, m
The antenna has the following design characteristics: gain relative to an isotropic radiator is 11.5 dB at 14 MHz and 12 dB at 21 MHz; the ratio of the radiation forward/ backward about 30 dB in both bands; the ratio of the radiation forward/sideways - more than 35 dB in both bands; SWR at the operating frequencies of about 1.
This antenna, which, in our opinion, deserves attention, " three "square" on three ranges, built by the American radio WA7NFH. Data are also given in table. 2.
The input impedance of this antenna on all bands less than 50 Ohms, so it is advisable to use gamma-matching device. The author used a special transformer on a ferrite ring, ensuring the coordination of all ranges (SWR=1) with one 50 Ohm coaxial cable. The antenna has very good characteristics on the bands 21 and 28 MHz, satisfactory at 14 MHz band and very compact dimensions (length of traverse of all of 4.88 m).
Antenna settings WA7NFH defined by calculation, respectively, 14, 21 and 28 MHz are as follows: gain relative to an isotropic radiator-10, 11.5 and 12 dB, the ratio of the radiation forward/backward - 27, 30 and 28 dB.
The last three-element antenna "square", which, we believe, should be shown (as a negative example), is a three-element "square" on 14 and 21 MHz, built by the canadian radio Amateur VE7DG (see tab. 2).
The author of the antenna cores reflectors and Directors, so on the 14 MHz band against the radiation forward/backward is only 15 dB. on 21 MHz 25 dB.
From up antenna systems "square" is the most popular antenna WOAIW with the same distance between elements (3,05 m), is designed to work on 14, 21 and 28 MHz (see tab. 3). Its input resistance on the bands 14 and 21 MHz to about 50, in the range of 28 MHz is about 40 Ohms. The author offers a direct connection to a 50-Ohm cable 14 and 21 MHz and 28 MHz through a section with a length of 175 cm 75-Ohm coaxial cable.
Frame length, m
The antenna has an optimal characteristics at 21, good-28 and satisfactory at 14 MHz. However, these "good" characteristics comparable with optimal characteristics of three-element of the "square". This, as well as very simple symmetrical design - that is, obviously, the reasons for the great popularity of the antenna W0AIW among radio Amateurs. Should be noted the potential of this antenna: it is possible to place two-element "square" on 7 MHz spacing between elements of 0.2 L.
The list of options "squares" could be further developed (construction of five - and chastisement antennas), but it seems to us, this is not necessary, as the main conclusions and recommendations which were made by the authors of the experiments and calculations, is well illustrated.
- K. Rothermel. The antennas. M.. "Energy", 1969.
- I. Chepu. Amaterske kratkovol-nove antenny. Bratislava, 1972. W. 0 r r. All about qublcal quad antennas. Radio publications Inc., Wilton, 1959.
- R. Fitz. Yagi vs quad. "QST", 1966. No. 11.
- J. Lindsay, Jr. Quads and yagls. "QST". 1968, No. 5.
- J. Parгоtt, Jr. Quad vs triband yagi. "QST". 1972, No. 2.
- Vladimir Beketov, K. Kharchenko. Measuring and testing when designing m regulation of Amateur radio antennas. M.. "Communication", 1971.
- A. A. Pistohlkors. The antennas. M., Svyazist. 1947.
- 3. Eisenberg. Shortwave antenna. M.. Svyazist, 1962.
- S. I. Nadenenko. The antennas. M.. Swashed, 1969.
- A. Snesarev. The active antenna with reflector. "Radio", 1968. No. 9, p. 17.
- V. Runners. Cable for remote adjustment of the antenna. "Radio", 1975. No. 7. S. 11.
- Radio No. 7, 1976