kv antenna. HF antennas Actively powered switchable dipoles
One of the most effective antennas for low-frequency DXing is a system of phased verticals, that is, two ... four vertical quarter-wave radiators (pin) located at a distance of 1/8 ... 1/4 wavelength from each other with direct excitation of each radiator by a separate power line . Such antennas, with external simplicity, have outstanding performance - gain from 4 to 7 dB with respect to a half-wave dipole at a height of 0.5 wavelength, back lobe suppression up to 20 ... 30 dB, vertical radiation angle from 15 to 30 degrees.
The point is small - to find a free area the size of half a football field, get two (or better - four) duralumin pipes with a height of a twelve-story building, and hire a helicopter to install them. Then you will have to put on a bunch of radio engineering primers in order to understand clearly what active power is, since the available amateur radio literature, unfortunately, practically does not provide the necessary information, and the antennas described in the classics of the Rothammel type have long been studied, and the next flipping of news does not bring .
Awareness of the foregoing, as a rule, does not add optimism, and therefore most radio amateurs on the TOP BAND manage with any Inverted Vee (for some reason stubbornly called "Inventor" by a certain part, apparently, of beginners, shortwavers), or "Delta", which, however, from - due to small (relative to the wavelength) heights, they are of little use for really long-distance communications. Some lucky ones manage to put shortened verticals up to thirty meters. Others may not read this article.
Thanks to the timely ideas of Eugene (RU6BW), after several sleepless nights at the monitor, the proposed design appeared.
The author in this article did not set out to go into theoretical depths regarding the operation of phased-feed antennas. Many are still skeptical about computer calculations in amateur radio practice. But this antenna works very well. For starters, you can try to build a "model" for 80 meters.
To begin with, let's consider the computer-simulated radiation patterns in the vertical (Fig. 1) and horizontal (Fig. 2) planes and graphs of the dependence of the back lobe suppression (Fig. 3) and gain (Fig. 4) on frequency:
- the width of the main lobe in the horizontal plane at the level of -3 dB - 136 degrees;
- the width of the main lobe in the vertical plane at the level of -3 dB - from 6 to 54 degrees (with a maximum of 20 degrees);
- suppression of the rear lobe: at a frequency of 1830 kHz - -22 dB, at 1845 kHz - -31 dB, at 1860 kHz - -19 dB;
- antenna gain - 5.3 ... 5.7 dB, respectively.
The indicated parameters were modeled for a grounding system consisting of 16 double-looped (along the perimeter and in the middle) counterweights 10 m long over soil of medium conductivity. At the power points, the outer ring is connected to two-meter pipes driven into the ground.
Isn't it true that an antenna with such parameters is very similar to a full-sized three-element "Wave Channel" at a height of 80 m? However, such a “monster” can only be dreamed of.
Let's analyze these numbers.
1. A horizontal lobe of 136 degrees, when switching radiation to the opposite, without much loss in gain, will block most of the directions (however, it is still desirable to orient the antenna along your favorite azimuths). In RU6BW conditions, this is 80/260 degrees.
2. A vertical lobe will handle reflections at distances from hundreds to thousands of kilometers with equal ease.
3. Gain within the working area practically does not change.
4. The suppression has decent characteristics in the region of only 30 kHz, however, the DX window overlaps. The question of how to expand the site will be discussed below.
The antenna is a system of two identical vertical half-wave loop vibrators with active shunt power. To reduce the height and simplify the design, the upper corners of the vibrators on the insulators are reduced to the top of the mast with a height of 25.00 m (in the 3.75 ... 3.8 MHz section, the mast height is 13 m; range) and are separated from it by 0.20 (0.20) m. The presence of an uninsulated metal mast of the specified length inside the frames does not affect the parameters of the antennas.
The four upper parts of the vibrators, each 25.88 (13.04) m long, diverge from the mast at right angles, descending to the ground to a height of 6.00 (3.00) m. In these places, the vibrator web is passed through the insulator and, bending, leaves to the feed point located 10.00 (4.72) m from the base of the mast. Four braces are attached to the insulators, serving as a continuation of the upper parts of the vibrators, together with which they fasten the top of the mast (similar to the elements of a dual-range Inverted Vee). The length of the part of the vibrator from the insulator to the power point is 14.07 (6.08) m (Fig. 5 and 6).
The frames are made of cord or bimetal with a diameter of 3…4 mm.
Two 10.00 (4.72) m lengths of 75-ohm cable are connected to opposite frames and converge to the base of the mast. One end of the frame is connected to the grounding system, the other - to the central conductor. Near the mast, the cable braids are also grounded, and a phase-shifting capacitor is connected between the central conductors. The direction of radiation is changed by connecting the output of the matching device to the corresponding end of the capacitor (by means of a relay controlled from Shack). The power cable from the transceiver is connected to the input of the matching device. The scheme of the matching device can be any. The tested antenna used a resonant autotransformer.
Setting
The whole process takes place on the ground under the mast and on the operator's table. With precise manufacturing, it is not necessary to select the length of the vibrators.
1. Set up the transceiver in the middle of the working area. We turn on instead of the phase-shifting capacitor KPI with a maximum capacitance of 1000 pF. At the input of the matching device, we install an SWR meter designed for measurements in lines with the resistance of the cable used (both 50 and 75-ohm coax can be matched). We set the phase-shifting KPI to the middle position.
2. In the case of using a resonant autotransformer, we adjust the matching device for the minimum SWR by selecting the tapping point of the circuit and the parallel capacitance. It is advisable to first coordinate the active load with the resistance of the cable used, and then do not change the setting.
3. The next step is to set the phase shift. We launch a beacon with a vertically polarized antenna a few hundred meters in a direction perpendicular to the plane of the frames. The author used a 1845 kHz oscillator with a KT922 amplifier, loaded on the TV antenna drop cable braid, located one and a half kilometers from RU6BW. As a last resort, we tune the transceiver to a working station located in the alignment of the frames, closer to the middle of the working area. We turn on the opposite frame (you can navigate by the drop in the signal level) and adjust the KPI for the maximum suppression of the beacon signal.
4. Repeat steps 2, 3, 4 until the forward / backward ratio is at least 4 ... 5 points.
5. If the SWR changes greatly during switching, it means that errors were made when cutting the antenna sheet, or conductors or other reflectors are located near one of the frames. After setting the frames, the above procedures must be repeated.
6. After the final adjustment, you can measure the capacitance of the KPI and replace it with a good quality fixed capacitor with an appropriate reactive power.
Note
Good suppression of the rear lobe, unfortunately, is obtained in a rather narrow frequency band. The result is excellent. Now, almost at any point in the range, without changing the geometric dimensions of the antenna, it has become possible to quickly and effectively suppress the signals of stations located in the back sector with a width of about 90 degrees. If desired, the same can be done manually, but with much less convenience.
The above computer calculations after the production of the system in kind and on-air run-in (TNX RU6BW) were fully confirmed. It seems that this is a very good alternative to Inventor at almost the same cost.
However, I would like to add the following.
Unfortunately, a certain part of radio amateurs thinks that the presence of an antenna with the described parameters automatically guarantees the work of, say, Ukraine with Asia at any time of the day (for example, at lunchtime). I have to disappoint TOP BAND so named because this is a range of the highest category of complexity, and for serious achievements on it you need to know a lot and work hard. Methods for obtaining results are described. The above development is just one of the effective options, I hope, a fairly affordable design.
When making a GP for low frequency bands, radio amateurs are usually forced to choose between antenna efficiency and antenna size.
Since the effective height of the GP band of 80 meters is about 13 m, it should be expected that with the optimal use of “extending” elements, an antenna of this length will be quite effective. You can tune a short antenna into resonance with a capacitive end load and / or an inductor.
A capacitive load is usually performed in the form of several conductors located perpendicular to the radiator web and located at its top.
This type of matching ensures the maximum efficiency of the antenna and, therefore, is a priority. From design considerations, the length of the conductors is chosen no more than 0.03 * lambda, which limits the possibilities of this method.
The use of an inductor is less desirable, since it significantly reduces both the efficiency of the antenna as a whole and its operating frequency band. However, both methods are often used in practice to effectively shorten the antenna. The losses in the coil can be reduced if it is made in the form of one or two turns of a sufficiently large diameter.
Although such inductors are more difficult to manufacture, they provide a large bandwidth (with a coil diameter of about 0.01 * lambda, it works partly as an emitter).
Antenna design
The advantage of this design is also that the coil introduces a certain capacitance relative to the ground, which additionally shortens the antenna.
Rice. 1. The design of the HF antenna.
The combination of these two methods is used in the antenna for the range of 80 meters (Fig. 1) The base of the antenna is a metal pipe protruding above the ground by 3 m. In the lower part, five radially diverging and deepened by 10 cm into the ground ground wires 25 m long are attached to the base .
Earth wires are made of galvanized steel wire. In the upper part, six radially divergent counterweights 19 m long are connected to the base.
A radiator 10.5 m high is fixed on the base (through an insulator), consisting of two pieces of metal pipes 3 m long (lower) and 7.5 m long (upper). The sections of the emitter are mechanically connected to each other through an insulating sleeve with a cross on which the inductance coil L is located.
The design of the inductor L is shown in fig. 2. Four bamboo sticks 1 m long are fixed in the insulating sleeve. Porcelain roller insulators are installed at the ends of the sticks, and there are two such insulators on one of the sticks.
A coil made of an antenna cord with a diameter of 5 mm is fixed on these insulators and connected with its ends to the upper and lower parts of the emitter.
Rice. 2. The design of the inductor L.
The capacitive load at the top of the emitter is made of four segments of the antenna cord 2.5 m long and 35 mm in diameter electrically connected to it. stretched along the bam beech poles (fishing rods).
To prevent these poles from bending, they are supported by nylon cords. The emitter in the working position is held by two tiers of nylon stretch marks (four in each).
The antenna is fed with a 75-ohm coaxial cable 12 m long. A matching device is connected between the cable and the transceiver (see the article "Spiral GP for low-frequency bands" in "Radio'', 2000, No. 1 p. 64). The antenna performed well during operation on ultra-long distances, providing communication with all continents.
Ernest Osminkin (UA4ANV). R-06-2000.
One type of antenna is a square antenna. It is popular in some countries. In Russia, such an antenna in one element is not very common. Either due to a lack of information in our radio magazines and amateur radio sources, or for other reasons.
Let's look at its application on amateur radio bands, on 80-ku for example.
For the 80 meter range, take a field wire 84 meters long. Place all four corners at a height of 16 meters from the ground. At the resonant frequency, there will be approximately 120 ohms of active wave impedance. The bandwidth at the level of SW = 2 will be approximately 230 kilohertz. The diagram is circular in the azimuthal plane, in elevation to the zenith. The gain will be approximately 8.3 dbi. To match a 50 ohm cable, you will need a 75 ohm coax quarter-wave transformer. Connection point in the middle from one side. When connected in one of the corners, the characteristics almost do not change.
If this square is lowered to a height of 9 meters from the ground. The active resistance at the resonant frequency will be about 50 ohms, and it will be possible to feed directly with a 50 ohm cable. In this case, the gain will increase slightly, and will be about 9 dbi. The bandwidth will be noticeably narrowed, and will be only 90 kHz. What is not good.
It makes sense to use such an antenna design at a radio station when conducting only local radio communications - up to 800 kilometers, and feeding the web in the corner may be preferable.
Let's now place the antenna canvas not parallel, but vertically relative to the ground. We increase the perimeter to 85 meters so that the resonant frequency is in the middle of the 3650 kilohertz range. The bottom side of the square is about 2 meters above the ground. Polarization is horizontal - the connection point is in the middle of the bottom side.
What will happen in this version - a bandwidth of 140 kilohertz. Few, and the entire 80-meter range covers very little, only a few antennas in the bandwidth.
The gain is less than 7 dbi. The diagram is circular, and all antennas from one element at a low suspension height have a circular diagram, whatever one may say, and do not tilt.
But the maximum radiation angle was 65 degrees. With such an angle, communication can be carried out both in the near zone and up to 3-5 thousand kilometers with equal success. You can even show a picture here.
We've looked at horizontal polarization, let's try vertical. To do this, we move the feed point to one of the midpoints of the vertical side. ABOUT! Miracle. The bandwidth was 330 kilohertz, which is very good, with a perimeter of 83.4 meters. Radiation angle maximum 16 degrees. With this angle, all DXs at 80k will be ours. That is, it will be possible to make good and simple connections from 5 thousand kilometers to the antipode (16 thousand km). Super!
The resistance in this case will be 200 ohms, and we can use a transformer ¼ in resistance, and everything will be fine.
Considering, trying, analyzing, any radio amateur will be able to choose, pick up a square antenna for himself. She is good.
In one of his books in the late 80s of the twentieth century, W6SAI, Bill Orr proposed a simple antenna - 1 element square, which was installed vertically on one mast. The W6SAI antenna was made with the addition of an RF choke. The square is made for a range of 20 meters (Fig. 1) and is installed vertically on one mast. In continuation of the last knee of a 10-meter army telescope, fifty centimeters piece of texto-textolite is inserted, the shape is no different from the upper knee of the telescope, with a hole at the top, which is the top insulator. The result is a square with an angle at the top, an angle at the bottom and two angles on the extensions on the sides. From the point of view of efficiency, this is the most advantageous option for placing the antenna, which is located low above the ground. The power point turned out to be about 2 meters from the underlying surface. The cable connection node is a piece of thick fiberglass 100x100 mm, which is attached to the mast and serves as an insulator. The perimeter of the square is equal to 1 wavelength and is calculated by the formula: Lm = 306.3 \ F MHz. For a frequency of 14.178 MHz. (Lm \u003d 306.3 \ 14.178) the perimeter will be equal to 21.6 m, i.e. side of the square = 5.4 m. 0.25 wavelength. This piece of cable is a quarter-wave transformer, transforming Rin. antennas of the order of 120 ohms, depending on the objects surrounding the antenna, the resistance is close to 50 ohms. (46.87 ohms). Most of the 75 ohm cable segment is located strictly vertically along the mast. Further, through the RF connector is the main transmission line cable 50 ohms with a length equal to an integer number of half-waves. In my case, this is a segment of 27.93 m, which is a half-wave repeater. This method of powering is well suited for 50 ohm equipment, which today in most cases corresponds to R out. Silos of transceivers and the nominal output impedance of power amplifiers (transceivers) with a P-loop at the output. When calculating the cable length, you should remember about the shortening factor of 0.66-0.68, depending on the type of plastic cable insulation. With the same 50 ohm cable, an RF choke is wound next to the mentioned RF connector. His data: 8-10 turns on a 150mm mandrel. Winding coil to coil. For antennas on the low bands - 10 turns on a mandrel 250 mm. The HF choke eliminates the curvature of the antenna pattern and is a Shut-off Choke for HF currents moving along the cable sheath in the direction of the transmitter. The antenna bandwidth is about 350-400 kHz. with SWR close to unity. Outside the passband, the SWR rises strongly. Antenna polarization is horizontal. Stretch marks are made of wire with a diameter of 1.8 mm. broken by insulators at least every 1-2 meters. If you change the feeding point of the square, feeding it from the side, as a result we get a vertical polarization, more preferable for DX. Use the same cable as for horizontal polarization, i.e. a quarter-wave length of a 75 ohm cable goes to the frame, (the central core of the cable is connected to the upper half of the square, and the braid to the bottom), and then a multiple of half a wave of a 50 ohm cable. The resonant frequency of the frame when changing the power point will go up by about 200 kHz. (at 14.4 MHz.), so the frame will have to be slightly lengthened. An extension wire, a cable of about 0.6-0.8 meters can be included in the lower corner of the frame (in the former power point of the antenna). To do this, you need to use a segment of a two-wire line of the order of 30-40 cm. Wave resistance does not play a big role here. A jumper is soldered on the loop at a minimum SWR. The radiation angle will be 18 degrees, not 42, as with horizontal polarization. It is highly desirable to ground the mast at the base.
Antenna horizontal frame
Antennas. antennas 2 antennas 3 antennas 4
LW Antenna
I consider it necessary to publish a description of the LW-82 m antenna (in common parlance - a rope). The fact is that this antenna, at minimal cost - no feeder, no need to go to the roof (it’s enough to live on the 2nd floor and have a suspension point at a distance of more than 80 m from your house) has very good parameters and allows you to start working on the most interesting ranges 160, 80, 40 m.
A description of such an antenna is also in the book "HF-VHF Antennas" by the authors Benkovsky, Lipinsky, fig. 5-20. A very important note: the tuner for this antenna must have a good radio ground, and these are only quarter-wave counterbalances for each band, in the worst case, your home's heating system. The diagram of the simplest tuner for such an antenna is presented below:
Coil L1 is wound on a frame with a diameter of 40 mm with a wire with a diameter of 1-1.25 mm and contains 50 turns with a winding length of 70 mm. The coil has taps from the 13th turn (range 40 m), counting from the right and from the 23rd turn, counting from the right (range 80 m); when the taps are not used, the entire coil operates on the range of 160 m. Naturally, to the right of the 13th turn, taps can be made for the ranges of 20, 15, 10 m. Suvorov (UA4NM). At your tuner, of course, the turns will have to be selected individually according to the SWR meter turned on before the tuner, or, in the simplest case, according to the maximum air noise on a given range or according to a neon light bulb for transmission.
Vladimir Kazakov
Effective 145 MHz balcony antenna
I needed a universal antenna with good characteristics to work in different conditions at 145 MHz, for example, from home, when it is not possible to install an antenna on the roof, from a car, in a parking lot and of course on a hike. After going through different designs, I settled on a two-element directional antenna. Despite the simplicity (I would even say: banality) of the design, it has many advantages, and ease of manufacture allows us to call it a "weekend design".
In the photos you can see how this antenna is installed on my balcony. The design turned out to be strong, rain and strong wind are not afraid of it. Before that, on the balcony, I had several different antennas: a zigzag without a reflector, branded A-100 and A-200, but it was this design that proved its effectiveness, so I removed the rest of the antennas as unnecessary. When installed on the roof, 2 el. at 145 MHz they do not play a 3x5 / 8 collinear antenna, I tested the A-1000 with a length of 5 meters. When tested, at a distance of 50 km, the signal from the A-1000 and the 2-element antenna was the same. It should be so because the A-1000 has a real gain of about 4 dB, and the one described here is 2x el. antenna 4.8db. She has always outperformed any car antenna type: 1/4, 1/2, 5/8, 6/8, 2x5/8. If two such antennas are phased together, they confidently outperform the A-1000. Check it out for yourself and see for yourself.
Consider the design, it is very simple (although perhaps not beautiful in appearance, I made it in 40 minutes) and consists of a 1002 mm long reflector and a 972 mm split vibrator (gap for a 10 mm cable). The distance between the reflector and the active element is approximately 204 - 210mm. The elements themselves are made of 4mm insulated wire. If your wire is different, you need to adjust the dimensions. Close the soldering points with raw rubber so that moisture does not get in. SWR from 144 to 146 MHz, approximately 1.0 - 1.1, measurements were carried out by the SWR-121 device.
The input impedance of the antenna is 12.5 ohms, for optimal matching with a 50 ohm cable, I used a transformer made from two pieces of a fifty ohm cable. They should have the same length of 37 - 44 cm (select more precisely when setting up) each. Both pieces of cable must be pressed against each other along the entire length. That's actually all. I recommend this antenna to everyone, instead of pins, zigzags, branded collinear antennas and other nasty things, on which they write clearly overestimated gain! If we compare it with two squares, then with approximately equal gain, you will need 4 meters of wire for two squares, and only two for this antenna. For two squares, you will need a stronger stick, because they will be noticeably heavier. The difference in gain is 0.3 dB, which is completely insignificant with real QSOs, but the suppression on the sides and back of 2 ate. antennas are much smaller and this is also a plus, because we need a circular radiation pattern.
High gain option
Many people ask how to further increase the gain of the described antenna and at the same time maintain a wide lobe. When adding elements, the branch will not only increase the gain, but also the petal will greatly narrow. Everything is very simple, you need to phase several antennas of the same type. The figure shows how to do this. The easiest way is to phase 2 or 4 antennas, you only need to space them vertically, because horizontal spacing will also narrow the main lobe. Since the described antenna has a weak directivity, you will get an antenna with high gain and an almost circular pattern. Another important plus of connecting several antennas of the same type is the improvement in the reception quality of mobile stations on the move. Yes, yes, mobile stations will be received much better on this simple design than on various branded pins 5 - 7 meters long (type A-1000, 3x5/8, etc.). I also recommend installing such antennas in cities that are surrounded on all sides by mountains. Now numerous reflections that appear in such places will work for you. Under such conditions, 2 x 2 will really outperform "solid" multi-element antennas. The actual amplification of the design of two antennas is approximately 7.3 dB. But keep in mind that it will receive better than a single antenna with a real gain of 8-10db. Four phased antennas will have a gain of 12.3 dB, while the directivity will be almost circular! No single antenna can compete with it!
Hiking option
After some time, a collapsible version of the antenna was made, for hiking and expeditions. Field tests have confirmed its good efficiency, it is not inferior to collinear antennas 3-5 meters long (2x5/8 or 3x5/8) at a range of up to 50 km and outperforms them at distances of 90 km or more. The photograph shows a field version of the antenna, disassembled. It takes 30 seconds to assemble the antenna. As a boom, a water plastic pipe is used, 510 mm long and 21 mm in diameter. The dimensions of the elements have been slightly adjusted because a different wire was used. For such a small antenna, there will always be a place in your backpack, and at high altitudes, in the mountains, you will not have to exert excessive effort to hold it (those who have been at 4000 and above know what I'm talking about). The whole cable and transformer are inside a plastic pipe, this protects them from accidental breaks and moisture. The antenna can be repaired right on the trip, it is enough to straighten the bent elements by hand, and so on.
50 ohm antenna option
At the request of "lazy people" who did not want to make a transformer, I calculated an antenna with a resistance of 50 ohms, for direct connection to the cable going to the radio station. The appearance has remained the same. The cable is connected directly to the active element, to improve balancing, I recommend making one turn around the ferrite ring, as close as possible to the soldering point. The gain of this version of the antenna is somewhat less and is approximately 4.3 dBd. Dimensions are given for 4 mm wire, if you have a different material, you need to adjust the dimensions. The distance between the reflector and the active element must be chosen more precisely, within 415 - 440 mm, until the minimum SWR is obtained.
A simple tri-band antenna
The antenna is operational in the ranges of 40, 20, and 10 meters. As a matching element, a transformer was used on a ferrite ring of the VCh-50 brand with a cross section of 2.0 cm. The number of turns of its primary winding is 15, the secondary winding is 30, and the wire is PEV-2 with a diameter of 1 mm.
When using a different section, it is necessary to re-select the number of turns using the diagram shown in the figure.
As a result of the selection, it is necessary to obtain a minimum SWR in the range of 10 m. The antenna made by the author has an SWR:
1.1 - on the range of 40 m;
1.3 - on the range of 20 m;
1.8 - on a range of 10 m.
V. Kononovich (UY5VI). "Radio" No. 5/1971
Indoor antenna 20 meters
L1=L2=37 turns on a frame with a diameter of 25 mm and a length of 60 mm of wire with a diameter of 0.5 mm. J1 connector in a small plastic case.
Compact Antenna Tuner
The circuit works fine and matches the antenna from 80s to 10s. Losses in the tuner when checking at 50 ohms surprisingly did not find a load at all. What is bypassing 100 W, what is through a tuned tuner 100 W, on all ranges from 80 to 10 .... The coil, although compact, is cold ... The resonance is quite sharp, and this tuner can be perfectly used as a preselector .
With SW-2011, everything works great in general, because. there is no DFT in it and the tuner plays the role of a preselector, which has a very favorable effect on the quality of reception. Many do not recommend using “Amidon” rings, as they do in the “west”, in these tuners - they are both expensive and heat up (introduce losses). meaning. An ordinary coil on a plastic frame is much
better. From experience - the diameter of the frame for power up to 100 W does not really matter - I checked from 50 mm to 13 mm in the latter version. No difference. The main thing is to withstand the total coil inductance of about 6 μH, and proportionally recalculate the taps (or choose specifically for your antenna)
KPIs are critical components. With a small gap, they “flash” them, because the voltage across them reaches hundreds of volts. But nevertheless, even with small capacitors, I achieved normal operation (without breakdowns at 3.5 and 7 MHz, as I had at first) by introducing the SW2 toggle switch, which switches the antenna output tap on the 3.5 and 7 MHz bands to most of the turns coils. This achieves a reduction in voltage across the capacitors when tuning the tuner.
Short vertical antenna
The vertical antenna described below, intended for operation on the 80m band, has a total height of just over 6m.
The basis of the antenna design is a pipe 2 with a diameter of 100 mm and a length of 6 m, made of a dielectric (plastic). Inside the pipe, to give it mechanical strength, there is a wooden block 3 with spacers 4 that are in contact with the inner surface of the pipe. Antenna mounted on base 7.
Approximately 40 m of single-core copper wire 5 with a diameter of 2 mm, having moisture-resistant insulation, is wound around the pipe. The winding pitch is chosen so that the entire wire is evenly wound around the pipe. The upper end of the wire is soldered to a brass disk 1 with a diameter of 250 mm, and the lower end is connected through a variable capacitor 6 to the central core of the coaxial cable 8. This capacitor should have a maximum capacitance of about 150 pF and in quality (nominal voltage, etc.) not must be inferior to the capacitor used in the resonant circuit of the transmitter output stage.
Like any vertical antenna, this antenna requires a good ground or counterweight 9. Tuning and matching the antenna with the feeder is done by changing the capacitance of the capacitor 6, and if necessary, changing the length of the wire wound around the pipe.
The quality factor of such an antenna is higher and, therefore, its bandwidth is narrower than that of a conventional quarter-wave vibrator.
Built by a radio amateur WA0WHE a similar antenna with a counterweight of four wires has an SWR of up to 2 in a bandwidth of about 80 ... 100 kHz. The antenna is powered by a coaxial cable with a wave impedance of 50 ohms.
Ground Plane on 5 HF bands
The proposed version of the antenna can be classified as a "weekend design", especially for those shortwaves that already have a 20-meter GROUND PLANE station on their station. As can be seen from the figure, in the center of the antenna there is a duralumin pipe with a diameter of 25 ... 35 mm, which acts as a carrier mast and a vertical quarter-wave element for a range of 20 m.
At a distance of 402 cm from the base of the pipe, a fiberglass plate with dimensions of 60x530x5 mm was fixed with two M4 screws. The ends of four-wire (3 mm in diameter) vertical elements are attached to it, the electrical length of which corresponds to a quarter of a wavelength for the middle of the 17, 15, 12 and 10 m bands.
A fiberglass plate measuring 180x530x5 mm is screwed to the lower end of the pipe with two M4 screws. An aluminum plate measuring 15x300x2 mm with five holes 4.5 mm in diameter is placed under the lower edge of the pipe, through which five M4 screws are passed, which are used to fasten the wire elements and the pipe. In order to have the best electrical contact, a piece of copper wire is inserted between the pipe fastening screws and any nearest wire element.
At a distance of 50 mm from the aluminum plate, another one of the same size is fixed, but with 6-12 holes, which are used to mount radial counterweights (six for each range).
The antenna is powered by a coaxial cable with a characteristic impedance of 50 ohms.
The dimensions of all elements and counterweights are indicated in the table. The distance between the vertical elements is 100 mm. Due to the windage of the antenna, it is fixed with two tiers of nylon guys. The first tier is fixed at a distance of 2 m from the base of the pipe, the second - at a distance of 4.1 m.
If there is a "GROUND PLANE" at 40 m, then using the described principle, you can create a 7-band antenna.
Indoor broadband...
The broadband indoor active loop antenna by S. van Ruji increases the reception efficiency of radio stations of all KB bands (3-30 MHz) by about 3-5 times compared to the telescopic one. Due to the fact that loop antennas are sensitive to the magnetic component of the electromagnetic field, electrical interference generated by various household appliances is significantly weakened.
Interference-proof shortwave receiving antennas
(Review of materials from the magazine "QST", 1988)
Many fans of long-range shortwave radio reception, as well as shortwave radio operators interested in conducting DX radio communications, especially on low-frequency HF bands and having only a vertically polarized GP antenna at their disposal, often face the problem of providing interference-free radio reception in practice. "Moreover, in the conditions of large industrial cities, it is the most significant. The signals of DX radio stations are often quite small, while the field strength of industrial, atmospheric, etc. interference at the receiving point can be quite high. In this case, it is necessary to solve the following problems :
1 - attenuation of these interferences at the RPU input with the least attenuation of the useful signal;
2 - providing the possibility of receiving radio signals in the entire shortwave range, i.e. broadband antenna-feeder device;
3 - the problem of providing sufficient area to place the antenna away from sources of additional interference. A significant decrease in the level of atmospheric, industrial, etc. Interference can be achieved by using special low-noise receiving antennas. In the literature they are referred to as "Low-Noise Receving antennas". Some types of such antennas have already been described in (1, 2, 3). This review summarizes some interesting results of experiments in this area obtained by foreign radio amateurs.
EXPERIMENTAL SHORTWAVE RECEIVING ANTENNAS WITH LOW NOISE LEVEL
Starting to engage in long-range radio reception on HF, you must first think about a good pseudo-protective antenna, this is the key to success. As already noted, the task of an anti-jamming antenna device includes the greatest possible degree of interference attenuation with the least attenuation of the useful signal. It is impossible to talk about the amplification of the useful signal by the receiving antenna, and especially on the low-frequency HF bands, for known reasons, because such an antenna will take up a lot of space and have a pronounced directivity. In some cases, to amplify the received signal, it is advisable to use preamplifiers between the RPU and the antenna, providing them with manual gain control (1). This also applies to antennas, which will be discussed later. These antennas are a modification of the Beverage antenna, the classic version of which is shown in Fig. 1a. This antenna is widely used in professional HF radio and has some anti-jamming properties. W 1FB experimented with a modification of the Beverage antenna and got interesting practical results, which he published in the April issue of the journal "QST". Some shortwavers considered them an April Fool's joke, while others, on the contrary, supplemented these results with their practical experience. In Fig.1b. an antenna is shown with the exotic name "Snake" (which means "snake"). It consists of a long piece of coaxial cable placed on the ground or in grass. The far end of the cable is loaded on a non-inductive resistor with a resistance equal to the characteristic impedance of the cable. This resistor must be placed in an insulating box and sealed to prevent moisture from entering the coax cable.
Since it turns out to be quite expensive to make such an antenna for low-frequency KB bands, due to the high price of the cable, W 1FB proposed to make an antenna from a two-wire ribbon cable or wire for a telephone or radio broadcasting line.
The wave impedance of such lines is different and can
be determined from the tables, as well as experimentally. When determining the length of this antenna, it is necessary, as in the first case, to take into account the shortening factor. An antenna in the form of a two-wire loaded line for a range of 160 meters should have a length of about 110 meters. Placing such an antenna above the ground is quite difficult, and W 1FB laid a cable around the perimeter of its site. At the same time, the main properties of the antenna are preserved if there are no foreign objects nearby that can affect the characteristics of the antenna and be a source of additional noise. These can be vertical antenna grounding systems, various metal pipes, fences, etc. When placing the antenna along the perimeter of the site, its directional properties are weakened and it begins to receive signals from different directions. In this design, it is important to accurately determine the characteristic impedance of the applied two-wire line. This is necessary for the correct calculation of the matching broadband transformer and load resistor, the resistance of which must be equal to the characteristic impedance of the applied line. The transformation ratio is chosen depending on the coaxial cable used. It is equal to:
R H / R K -(N/n) 2
Where: R H - resistance of the load resistor, Ohm;
R K - wave impedance of the coaxial cable, OM;
N is the number of turns of the transformer winding from the antenna side;
N is the number of turns on the receiver side (power line).
On fig. 1g the antenna proposed by W 1HXU is shown. It is located above the ground and is made of a ribbon cable with a characteristic impedance of 300 ohms. To adjust it, a variable capacitor with a capacity of up to 1000 pF was used. The capacitor is adjusted to the highest level of the received signal. Figure 1e shows a "Snake" type antenna made of a coaxial cable a little over 30 meters long, which is laid in the ground. The far end of the cable has a connection between the central core and the braid. At the "receiving end", the braid does not connect to anything. W 1HXU tested this antenna with good results on 30, 40 and 80 meters.
CONCLUSION
When making antennas with a low level of interference, it should be borne in mind that they attenuate the useful signal quite strongly, so the use of antennas from coaxial cable is justified only in cases of a very high level
industrial interference at the receiving point. As already noted, in these cases
it is advisable to use additional amplifiers. Antennas made of a two-wire balanced line in a tape dielectric have less attenuation of the useful signal and give more confident results. It should also be noted that the use of all the antennas described above is possible only if there is
in the RPU input, designed to connect antennas with a wave impedance of 50 or 75 ohms. If there is no such input, then it is necessary to use an additional coupling coil, which can be wound over the coil of the RPU input circuit for the HF band on which you expect to use these antennas. The number of turns of the coupling coil is from 1/5 to 1/3 of the number of turns of the HF band loop coil. The connection diagram of the additional coil is shown in Fig.2.
Multi-band antenna with switchable radiation pattern
The problem of creating a sufficiently efficient multi-band antenna in a limited space, requiring relatively low costs, worries many radio amateurs. I want to offer another version of the "poor amateur radio" antenna that meets these requirements. It is a beam switching slopper system operating on the 3.5, 7, 14, 21, 28 MHz bands. It is based on the principle of operation of RA6AA and UA4PA antennas. In my version (Fig. 1), from the top of a 15-meter mast at an angle of about 30-40 ° to the ground, 5 beams go, which simultaneously act as the upper tier of guys. There can be more beams, but preferably at least 5. The total length of each beam is 21 m, about 80 cm are deducted from it for the outlet to the relay box and about 15 cm for the insulator mount at the bottom of the beam. Thus, the actual length of each beam is about 20 meters. The antenna is powered by a coaxial cable with a wave impedance of 75 ohms, about 39.5 meters long. The length of the cable is critical - together with the length of the beams, it should be 1 wavelength on a range of 80 meters. All rays in the initial state are connected to the cable sheath. The choice of the required direction is made directly at the workplace, while the corresponding relay connects the beam of the selected direction to the central core of the cable. As with most directional antennas, the suppression of the side lobes is more pronounced than the back one, and averages 2-3 points, less often - 1 point. A comparison was made with a log-periodic RB5QT antenna suspended at a height of about 9 m above the ground in an east-west direction. At 7 MHz, sloppers won in these directions by 1-2 points.
Design. The mast is telescopic, from R-140, stands on the ground without additional grounding, without dielectric inserts. Beams - from a P-275 field telephone cable (2 wires of 8 steel and 7 copper conductors each), well soldered using acid. Coaxial cable 75 Ohm. It is possible to use a cable with any wave impedance, as well as an open two-wire line with a resistance of 300-600 Ohm. The relay is used type TKE52 with a supply voltage of about 27 V with paralleled contacts, but others can also be used - based on the power of the transmitter. The relay is powered by a separate four-wire cable. Such a circuit (Fig. 2) allows you to power 6 relays, due to local conditions I have 5. To switch voltages, P2K buttons with dependent fixation are used. The dimensions of the antenna and the power line can be changed in any direction using the formula L2 = (84.8-L1 )*K, where L1 is the length of one arm, L2 is the length of the supply line; K - shortening factor (for a cable - 0.66, for a two-wire line - 0.98). If the resulting line length is not enough, instead of 84.8, substitute 127.2 in the formula. For a shortened version, you can substitute 42.4 m into the formula, but in this case the antenna will only work at frequencies above 7 MHz.
Setting. The antenna practically does not need to be tuned, the main thing is compliance with the indicated dimensions of the beams and cable. When measuring with an RF bridge, it turned out that the antenna resonates within the amateur bands, and its input impedance is in the range of 30,400 ohms (see table), so it is advisable to use a matching device. I used the UA4PA recommended parallel circuit with taps. In the range of 160 m, this antenna does not work - the resonant frequency of 1750 kHz is chosen so that in the remaining ranges the resonance is within the range.
| FREQUENCY | Zin, Ohm |
| 1750 | 20 |
| 3510 | 270 |
| 3600 | 150 |
| 7020 | 360 |
| 7100 | 400 |
| 10110 | 50 |
| 14100 | 260 |
| 14250 | 200 |
| 14350 | 180 |
| 18000 | 50 |
| 18120 | 50 |
| 21150 | 190 |
| 21300 | 180 |
| 21450 | 160 |
| 24940 | 59 |
| 25150 | 50 |
| 28050 | 160 |
| 28200 | 200 |
| 28500 | 130 |
| 29000 | 65 |
| 29600 | 30 |
