Published: March 31, 2016

Part one. I have been working on air for 5 years using only a magnetic antenna. There were several reasons for this: the main one is that there is no place to pull at least some “rope”, and the next thing is what I understood - the “correct” Magnetic frame” is far from worse, and even in many ways cases, even better than any wire antenna. When, back in Kharkov, I was experimenting with a magnetic frame, I had a mistrust of this antenna, although even there I received Magnitka better than a full-size Delta on the 160 m range. I also made a lot of mistakes then, about which I didn’t know either.

Then I had a full-size vertical “delta” of 160 meters, stretched between two 16-story floors. I mainly worked on 160 m. Somehow I got busy and whipped up a magnetic receiving antenna for this range. When tested during the day, in an apartment on the 8th floor in a reinforced concrete building, I confidently received a station located 110 km from Kharkov, while on the delta I heard only the presence of the station and could not receive a single word. I was amazed, but in the evening, when everyone came home from work and turned on the TV, I didn’t hear anything at all on the magnetic frame, just a continuous buzz. This was the end of my first experience.

And now here, in Toronto, I again had to work on magnetic antennas, but now also transmitting ones. At first I had a 20 m dipole on my balcony. Europe responded on 20 m, but rather weakly. Only those who have "Yagi" or a pin. And when I played “Magnitka”, they began to respond immediately, and not only those with “Yagami”. Communications have started with stations that have dipoles and “inverters” and “ropes”. Then I converted the dipole into a delta. The resulting perimeter was 12.5 m; I placed the extension coil 50 cm from the hot end of the delta. Now the delta began to be built by the tuner from 80 m to 10 m. In terms of noise, the delta is much quieter than the dipole, but it is difficult to compare with Magnitka. There are times when Magnitogorsk picks up more noise, and sometimes vice versa. It depends on the noise sources. There are connections with Europe and the delta, but the response is much worse. Magnitogorsk still wins. I read somewhere that a vertically located magnet has a radiation angle to the horizon below 30 degrees.

My first antenna of this size: the outer diameter of its pipe is 27 mm (inch copper pipe), the diameter of the antenna at the corners is 126 cm, the diameter of the antenna in the middle of opposite sides is 116 cm (measured along the axis of the pipe). The corners (135 degrees) are also copper. Everything is soldered. At the top of the antenna there is a cut in the middle of the side of the pipe, the gap is about 2.5 cm. At the top of the antenna in a plastic box there is a variable capacitor - “butterfly” with a motor direct current and a gearbox. The stator plates are soldered to copper strips, which, in turn, are soldered to the pipe on opposite sides of the gap; the rotor is not involved (there should be no current collection). The capacity of the variable capacitor is 7 - 19 pf. The gap between the plates is 4-5 mm. This capacity is enough to tune the antenna on the 24 MHz and 21 MHz bands. At 18 MHz an additional capacitance of 13 pF is needed, at 14 MHz - 30 pF, at 10 MHz - 70 pF, at 7 MHz - 160 pF. For these capacitors, clamps are soldered at the edges of the pipe cut (visible in the photo), which tightly press the terminals of additional capacitors (the tighter the better). Such precautions are necessary during transmission. At 100 W, in transmit mode, the voltage on the capacitor plates reaches 5000 volts, and the current in the antenna reaches 100 A. The diameter of the communication loop is 1/5 of the antenna diameter. The communication loop (Faraday loop) is made of cable, there is no contact with the antenna. The antenna is powered by a 50-ohm cable of arbitrary length.

But then I changed my place of residence and, at a new QTH, this antenna turned out to be too big. The balcony has a metal fence and therefore there was poor reception inside the balcony. It was necessary to move the antenna outside the balcony and I made the following magnetic frame.

Its frame is made of copper pipe with a diameter of 22 mm, the antenna diameter is 85 cm. It operates from 14 to 28 MHz. According to calculations for such antennas, this frame should work a little worse than the previous one, because the pipe is thinner and the diameter of the frame is smaller, but practical use has shown that the second antenna is in no way inferior to the larger frame. And my conclusion is that a solid pipe is still better than one welded from several pieces. At enormous currents, the slightest resistance at copper-tin junctions and vice versa, as well as at the terminals of additional capacitors, causes large losses. During reception this is imperceptible, but during transmission there is a loss of power.

I work in digital forms, mainly in JT65. On a smaller antenna at 28 MHz at 5 watts I worked with Australia (15,000-16,000 km), South Africa (13,300 km through my house). Then I redid the first frame, in which instead of a butterfly capacitor I installed a vacuum capacitor.

And, to my surprise, the antenna began to be built at 28 MHz and I added a 10 MHz range. Although at this range, according to calculations, the efficiency is 51%, I calmly carried out communications with Europe at 20 watts in JT65. The rework was done literally 2-3 weeks ago, so I don’t have the full picture yet. But one thing is clear - the antennas work. I control the restructuring of the capacitor remotely, from my workplace. The setup is quick, I get into resonance the first time, or at most the second time, i.e. I don’t experience any major inconvenience during the restructuring. And when working with digital modes, there is no need to adjust the range at all.

I would like to formulate several important criteria that must be taken into account when constructing an effective transmitting magnetic antenna. Maybe my experience will help someone and the person will not spend a lot of time and money like I did, especially since with the wrong approach to building a magnetic frame, interest in this type of antennas may disappear - I know this from myself. But a properly made antenna really works well. I emphasize that these are only my thoughts, which are based on my personal experience in the construction and use of magnetic frames. If anyone has any comments or additions or questions, please write to me by E-Mail.

1. The antenna sheet must be solid.

2. The material is copper or aluminum, but aluminum produces transmission losses that are about 10% greater for the same size than copper (according to various programs for calculating magnetic antennas).

3. The shape of the antenna is preferably round.

4. The antenna surface area should be as large as possible. If it is a pipe, then the diameter of the pipe should be as large as possible (as a result, the outer area of ​​the pipe will be larger), but if it is a strip, then the width of the strip should be as large as possible.

5. The antenna sheet (pipe or strip) must fit directly to the variable capacitor without any intermediate inserts of wires or strips soldered to the antenna sheet and to the capacitor. In other words, you need to avoid soldering and “twisting” in the antenna fabric whenever possible. If you need to solder something, then it is better to use welding, for copper it is copper welding, for aluminum it is aluminum welding, in order to avoid metal inhomogeneities in the antenna sheet.

6. The antenna sheet must be rigid so that there is no deformation, for example from wind loads.

7. The capacitor must be with an air dielectric and with a large gap between the plates, or even better - a vacuum one.

8. My capacitor and electric motor are closed in a plastic box. At the bottom of the box there are two small holes for draining condensate.

9. There should be no current collection on the capacitor, so you need to use a “butterfly” type capacitor in which the stator plates are connected to different ends of the antenna sheet, and the rotor is not connected to anything.

10. The communication loop has a diameter of 1:5 of the diameter of the antenna. It must be taken into account that as the diameter of the communication loop decreases, the quality factor of the antenna increases, and hence its efficiency, however, the bandwidth of the antenna narrows. I found information on the Internet that you can use a communication loop with a diameter of 1:5 to 1:10 of the diameter of the antenna frame. I am using a Faraday loop as a communication loop. I did not use gamma matching. For the communication loop, I use a cable with an outer diameter of 8–10 mm, whose shield is a corrugated copper tube.

11. In the immediate vicinity of the antenna I use a cable choke - 6-7 turns of the same cable, wound on a ferrite ring from the TV deflection system.

12. The antenna “does not like” metal objects, long wires, etc. near it. - this may affect the SWR and radiation pattern.

13. The height of the magnetic antenna above the ground for the maximum achievable efficiency of its operation must be at least 0.1 wavelength of the lowest frequency range of this antenna.

If you comply with the above requirements for constructing a magnetic frame, you will actually get good antenna, suitable for both local communications and DX work.
According to Leigh Turner VK5KLT: - “A properly designed, constructed, and sited small loop of nominal 1m diameter will equal and oftentimes outperform any antenna type except a tri-band beam on the 10m/15m/20m bands, and will at worst be within an S-point (6 dB) or so of an optimized mono-band 3 element beam that’s mounted at an appropriate height in wavelengths above ground.”
(A properly designed, constructed and properly placed 1m diameter magnetic antenna will be equivalent to and often superior to all antenna types except the tri-band wave channel on the 10m/15m/20m bands, and will be inferior (by about 6 db) to an optimized single-band 3 -x element antenna wave channel mounted at the proper height in wavelength above the ground) My translation.

Part two.

Wideband magnetic receiving antenna

Firstly, for the antenna I use the central core of the cable, the shield is grounded. The screen is torn at the top of the antenna at equal distances from the amplifier. The gap is about 1 cm.
Secondly, the amplifier is connected to the antenna via a WBT (broadband transformer) on a transfluor to reduce the penetration of the electrical component.

(save the diagram to your computer and it will be read better)
Thirdly, the amplifier has two stages, both push-pull (to suppress common-mode interference) using low-noise J310 transistors. In the first cascade, each arm contains two transistors in parallel with a common gate; the noise of the cascade is reduced by the square root of the number of parallel-connected transistors, i.e. by 1.41 times. There is an idea to put 4 transistors per arm.
Fourthly, the power supply should be as “clean” as possible, preferably from a battery.

Here I am posting the antenna diagram

The drain currents of all transistors are 10-13 mA.
On the 18, 21, 24 and 28 MHz bands I additionally use two switchable amplifiers (16db and 9db). They can be enabled one at a time or both at once. And, what is very important, on all bands, immediately after the antenna, I use additional 3-circuit DFTs (as in the RA3AO transceiver). Additional DFTs are needed since the antenna receives and amplifies all stations from the LW to FM range. All this ends up at the receiver input and can overload it, which will result in increased noise and deterioration of sensitivity, rather than in its improvement.

Today I conducted such an experiment. Along the perimeter of the antenna frame, with large steps, a thick stranded copper wire in insulation was wound. The total diameter of the wire is about 5 mm. I installed a two-section variable capacitor near the amplifier. The ends of the wire were connected to the stator sections of the capacitor. The result was a magnetic resonance frame that was not connected anywhere. The range of this design turned out to be as follows: about the minimum of one section of the capacitor - 20 m. Two sections in parallel - about the maximum of the capacitor - 80 m. I think if you add a permanent capacitor in parallel, then it will be 160 m. The received signal has increased (according to my subjective estimates, about 10 db minimum), the antenna's noise immunity has not deteriorated, the resonance is not sharp, the entire 20 m range is covered - the antenna only needs to be rebuilt when changing the range. Without touching the main antenna, the gain, selectivity and, most likely, sensitivity have increased.

Moreover, on all other bands the antenna receives in the same way as without an additional tunable circuit.

I thought for a long time about how to increase the sensitivity of the antenna in the upper ranges and decided to add another resonant frame. Here is a photo:

The diameter of the additional frame turned out to be small. The resonance is quite sharp, ranging from 20 MHz to 29 MHz. I haven’t tried it below, since there is another frame that is built on the lower ranges. On the large resonant frame, the variable capacitor was replaced with a “galetnik” with constant capacitors for the convenience of switching ranges.

I modified my receiving anti-noise antenna - I removed the additional circuits, turned the antenna upside down with the amplifier, and added two beams of 1.2 m of stranded wire from the bottom of the braid cut. I can’t add a longer wire; the size of the balcony is limited. In my opinion, the antenna began to work much better. The sensitivity has increased in the upper ranges of 21 - 28 MHz. The noises have dropped. And one more note - it seems that near stations have become quieter, and the reception level of distant stations has increased. But this is a subjective opinion, because... The antenna is located on the balcony of the 5th floor of a 19-story building. And, of course, there is the influence of the house on the radiation pattern.

Pictures upon request UA6AGW:

You can experiment with the length of the rays, but I don’t have that option. It may be possible to increase the gain a little in the desired range. Now my maximum reception is around 14 MHz."

Part three.

(From a letter) “Yesterday I quickly made a 10 m antenna. I am attaching a photo.

This is a converted antenna of 20 meter range which I did before. The length of the rays remained the same, about 2.5 m, I don’t remember exactly. and the antenna itself turned out to be 34 - 35 cm in diameter. Whichever piece of cable was left was what I used. As a result, I got the following. Both capacitors are at maximum capacity. In this position, the capacitors slightly fall short of 28.076 MHz. Those. resonance
it turns out to be 28140-28150 and higher in frequency. At first I wanted to cut off the rays, but after that I didn’t, because... the frequency will go even higher. I also installed a communication loop from a 20-meter antenna. As a result, at 28076 SWR it turned out to be 1.5 less and I couldn’t achieve it. But at the same time I decided to try working on air. Worked at 8 watts according to indications
wattmeter SX-600. I compared the reception of this new antenna with my wideband receiving antenna and I could see virtually no difference. On my antenna, the air noise is a little less, and the signals from the stations are almost the same level. I looked at all this on SDR. I started working on air on CQ in the morning. I was surprised at how actively they responded to my 8 watts and the reports they gave me. In the morning the passage was to Europe and these were all European stations. The reports I received were mainly to me
they gave, higher than I gave them. Now we need to change the capacitors and shorten the beams."

But the antenna was very capricious in tuning; with the slightest breeze, the rays moved and this affected the SWR. You could see the SWR meter needle dancing in time with the oscillations of the antenna beams. And I began to work further on this antenna with the goal of making its parameters stable and the antenna itself could be easily repeated. As a result, after lengthy discussions of the antenna with Vladimir KM6Z, we came to the conclusion that the internal conductor with a capacitor is superfluous (sometimes it can be harmful). I shorted the inner braided conductor at both ends of the antenna and removed capacitor C2. The antenna worked as well. Then, at the suggestion of KM6Z, I replaced the communication loop with gamma matching. After careful setup, I saw that the signal from the antenna increased. Next, again at the prompt of KM6Z, instead of gamma matching, I used T-matching or double gamma matching and performed the reduction with a two-wire 300 ohm line. The signal from the antenna has increased even more; I don’t use additional amplifiers, because... they are simply no longer needed and I noticed that the interference from the neighboring computer, which used to be constantly present, has disappeared, although the two-wire line runs next to this interfering computer. As a result, I rebuilt my meter magnetic frame, attached beams of about 2 meters, and made T-matching. As a result, I called the resulting antenna “MAGNETIC DIPOLE”. This new antenna has the following parameters - diameter 1.05 meters, antenna surface - copper pipe with a diameter of 18 mm, vacuum capacitor 4-100 pf, beams - 2.06 m. The antenna operates in 4 bands 30m, 20m, 17m, 15m. I adjust the SWR rules at 30 and 17 meters by adding 30 cm of wire to the beams. I work in digital modes JT9 and JT65, everyone responds with 10 watts, everyone hears (I look at PSK Reporter). Australia (14000-16000 km), New Zealand (about 13000 km) is not a problem at all. There is a connection with Thailand through the North Pole (and these are very problematic connections) on the same 10 Vats. I carry out connections for 3000 - 5000 km, even with weak travel, every day. Europe 5000 – 7000 almost every day. Even fed up with it.

Hi all!
Yesterday there were a couple of hours of free time left. I decided to implement an old idea - to make a magnetic antenna (magnetic frame). This was facilitated by the appearance of the Degen radio. Having made a magnetic antenna for the Degen radio, I was surprised - it doesn’t work badly!

Because They ask a lot about this antenna, I’m posting a simple sketch
Frame data

Sketch of a magnetic antenna for HF bands

• the diameter of the large frame is 112 cm (a tube from an air conditioner or car gas equipment), it is very convenient and inexpensive to use a gymnastic aluminum hoop
• the diameter of the small frame is 22 cm (material is copper wire with a diameter of 2 mm, it can be thinner, but the circle itself no longer holds its shape)
• The RG58 cable is connected directly to the small frame and goes to the radio receiver (you can use a 1 to 1 transformer to exclude reception on the cable)
• KPE 12/495x2 (any other can be used, the operating frequency band will simply change)
• range 2.5 - 18.3 MHz
• so that the frame begins to accept 1.8 MHz, add a 2200 pF capacitor in parallel

The idea is not new. One of the options is . This is a single turn frame. I got something like the following

The reception is wonderful even on the 1st floor of a private house. I am amazed. This simple magnetic antenna (magnetic loop) has selective properties. The tuning at low frequencies is sharp, at high frequencies it is smoother. With a conventional KPE 12/495x2 with one section, the antenna is operational up to the 18 MHz range. With the second section connected, the lower limit is 2.5 MHz.
I was especially impressed by the frame's performance on the 7 MHz band. It turns out to be an excellent magnetic antenna for Degena.

last video

If you don't understand, ask. de RN3KK

Added 06/19/2014
I moved to a new QTH, 9th floor of a 9-storey building. The standard telescope of the Sony TR-1000 receiver receives significantly fewer stations than the magnetic frame. + the very narrow bandwidth of the antenna makes it an excellent preselector. Alas, there is no magic, when the neighbor below turns on his plasma, the reception goes out everywhere... even at 144 MHz...

Added 08/18/2014
There is no limit to surprise. I placed this antenna on the loggia of the 9th floor. A lot of Japanese stations were heard in the 40m range (the range to Japan is 7500 km). Only one Japanese station was received in the 80m band on the same day. The antenna deserves attention. I couldn’t even think that long-distance reception was possible with this magnetic antenna (magnetic frame).

Added 01/25/2015
The magnetic frame also works for transmission. No matter how strange it may seem, they answer. It works not bad at 14 MHz, but at lower ranges the efficiency is no longer the same - you need to increase the diameter. Even with a power of 10 W, brought Powersave lamp glowed almost at full strength.

Article 2. Magnetic antennas (magnetic loop):

Antenna - a device for emitting and/or receiving electromagnetic waves by directly converting electric current into radiation (during transmission) or radiation into electricity(at reception).

Magnetic antenna(magnetic loop) is an antenna in which the emission and reception of electromagnetic waves is carried out due to the magnetic component; the electrical component is negligible and is usually neglected.

(On the ODLR.ru forum in November 2010, there was a discussion of one antenna - a broom, for a tube receiver, using a balcony version. I inserted my piece, and the result was an article.)

And so I’ll try to write it in the style of a true story.

But we are talking about antennas. I lived then in the military town of Kalininets, in the common people’s name “Alabino post office”. Every day in the morning, I took the bus to Golitsino, took the train to the Fili platform, then took the metro to Nogina Square (now Kitay-Gorod). then walk to Pokrovsky Boulevard, within the walls of his native alma mater. In the evening, the same route, but in reverse. And only on Fridays there was an exception to the rule; there was a stop in the Fili area.

My friend RA3AHQ lived not far from the platform; in the world he is Alexander Bolgarinov (now lives in Maryino). I took a couple of “fire extinguishers” and went to visit. Alexander had an imported Kenwood “TS-450” transceiver, which was very cool at that time. Such exceptions to the rules happened almost every week, and only on Fridays. One day we were sitting, sipping some red wine and turning the vernier knob, listening to the conversations of radio amateurs. My attention was attracted by an unusual structure on the windowsill, I ask if you are from Das, and Sasha says that this antenna is called a Magnetic loop and shows an article in the magazine Radio No. 7 for 1989, page 90, in the section for abroad. In a word, this is the article that Sergey Kashekhlebov cited in the discussion on the forum. I arrived home, begged a halohoop from a neighbor, and within two hours, I made my first radio communication on 40 m with Peter, my antenna was mounted on a board, the KPI was screwed to the halohoop (the duralumin is not soldered). This was my first experience, after which there were other experiences, but more on that later.

In 2000, I was hired by a company that dealt professionally with radio communication systems. There was one project in the Arctic, we went for testing. We took with us several types of antennas, these are traditional triangles, made of antenna rope, and spiral-pin ones, at the base of which there were automatic antenna tuners (Icom AT-130) and one ML (Magnetic loop) design, made of coaxial cable, corrugated braid 30 mm thick. The diameter of the emitter was 4 m, the antenna was fixed on an ordinary wooden pole with a cross, and attached to an iron trailer. Through certain time We get in touch, test the passage, draw up a daily passage schedule. And suddenly everything disappeared, there was only “white noise” on the air, and nothing more. They tell me on the phone from the base that there is a magnetic storm and a break for indefinite time. Out of boredom, I started clicking and switching antennas on the amateur bands. Imagine my surprise when I heard radio amateurs working on 40 meters. I'm for the microphone and let's go. I asked all the correspondents to listen to two more antennas, switched to “delta” and helical pin, and then ML, I didn’t hear anything on those antennas and they didn’t hear me either.

Later, I persuaded the commercial director to buy a couple of antennas in Germany; I wanted different sizes, but they bought the same type. At that time, production was established there and Christian DK5CZ was in charge of this (heaven rest in peace, the key was silent). But people are still continuing his work. So let's go back here. The German design was not practical, the emitter diameter was 1.7 m, solid, inconvenient for transportation. In general, we made our own antenna, the emitter consisted of three segments, the material was AD-30 (I took a piece of the German one for chemical analysis), the KPI was made in the form of a butterfly and had a capacity from 170 to 200 peaks, this made it possible to cover 3 amateur bands for transmission (160 m, 80 m and 40 m), with a radiator diameter of 4 m. But this is not the main thing, the main thing is how this antenna worked.

Everyone who visited our team probably noticed that in the immediate vicinity of the radio station (300-500 m) there are three power lines running in a semicircle, one of them is 500 kV. So our chatter is always 8-9 points according to the S-meter. And when I placed the ML horizontally on the roof (on pegs 1 m high), using it as a receiving antenna, then.... There was ZERO noise, and only a useful signal. Stations began to be heard that were at a level of 2-3 points, and which I would never have heard. This was on the 20m band.

Second. Our guests, approaching the school, saw amateur antennas on the neighboring house, this is a radio amateur, Alexander, he likes to participate in HF competitions in the single-band competition, on the 17th floor there are 2 Cushcraft 40_2CD elements, i.e. He sits at 40 meters and that’s it, but we are completely shut up. At 40 m the S-meter rests on the opposite wall, and at other higher bends it is no better. This went on for several years. And what do you think. When we installed ML for reception, it works at the beginning of the SSB section, 7.045 MHz, and we are at the end, 7.087 MHz, we don’t feel it, as if it’s not there.

There were also tests on the Northern Dvina River. An ML antenna was mounted on the ship (with a radiator diameter of 1.7 m - the same one - German). It was at the end of May, we were going downstream near the city of Kotlas, at about 3.00 on 40 m I heard ER4DX working for Latin America, Vasily. He has an antenna with several elements and a “kind” assistant. I asked to join the group, and using the S-meter I received signals from Latin American stations at 7 points, and the report from them received 7 points.

Yes, by the way, here is a link to the site: the DK5CZ site has everything there. And there is also the MagLoop4 program, which allows you to calculate magnetic frames, which can be made in the form of a circle, triangle, square, but here is the link, test it yourself: Magloop4 modeling program If you have any questions about using the program, I can conduct a master class, so to speak, or an open lesson . P.S. As a receiving antenna, a design made of a 10 mm copper tube (water pipe) was used and the capacitor was a variable one from a tube radio (tuned once to the middle of the range). And at the end of the article I will post a scan of the ML instructions.

Answer from one of the ODLR users. Inspired by Pavel’s unprecedented academic material, I remembered a sports apparatus (a gymnastic metal hoop), made by the famous Khrunichev rocket and space company and unnecessarily resting behind the sofa... I decided to experiment in a hurry... Within an hour of craft work, I made it from it antenna shown in the attached photos... The shunt capacitor (0.01 uF) was selected for maximum and purity of the weak useful signal... The result is wonderful! The reception is great! And if you take the structure outside the balcony, then you don’t need anything better! The concept is right! Very satisfied. Thanks Pavel! The topic has rapidly moved towards the exchange of specific practical results....

My answer. Alexander. All this is good that you did, but it seems to me that it will have the same effect if you place the container in an ordinary triangle or square made of ordinary wire. It looks like the capacitor plays the role of a shunt or filter plug (it seems so to me). The link to the DK5CZ website provides a schematic design of the MLoop antenna. It consists of an emitter and an excitation loop, their dimensions are respectively 5:1, look at the figure. The loop is made of coaxial cable, and it is not electrically connected to the emitter (in my designs), and I made my first halohoop in exactly the same way. But in other experiments, gamma matching was done instead of a loop. In other cases, the role of a capacitor was played by the air gap at the cut point of the emitter, then the perimeter of the emitter was equal to half the wavelength, by the way, this is confirmed by the program.

P.S. A friend of mine experimented with these antennas on the 145 MHz band and made a double antenna, i.e. two emitters located on one traverse (When viewed from above, the design looks like two wheels on the same axis). Khashnik was controlled. The result is very interesting, I mean the radiation pattern. And in comparison with a multi-element antenna, this design did not lose. Returning to the design of the antenna itself, it is my personal opinion that it is the antenna power system, be it a loop or another type, that gives the effect that the electrical component in the signal is negligible and is neglected, i.e. There is mainly a magnetic component. Hence the name of the antenna - Magnetic frame. Please note that the excitation loop is made specifically with cuts.

User responses. Pavel, I visited you more than once, but I wasn’t interested in antenna management, but in vain... Enlighten the people, take a photo to the studio, please.

Since there was no digital camera in those days, I used a point-and-shoot camera. By the way, I forgot. There was another experience of using it. I defended my diploma at the All-Russian Academy of Sciences using antennas of this type, the diploma was classified as “secret”, but I think that after many years it can be said about this, especially since there is one photo, this is a fragment of an explanatory note during the defense. This was in May 1990.

Then preparation for the field competition "Radio Expedition Pobeda". April 2000, roof of a school (which later became a testing site). And this is a trip to Volokolamsk, to the monument to sapper soldiers (May 8-9, 2000), we worked as RP3AIW. This is just an antenna made from a cable “on a cross”.

In September 2000, I was already in the Arctic. In the first photo there is an installation of a spiral-whip antenna with a tuner (9 m high, homemade) and a typo on the photo inscription, not 2001, but 2000. In the distance a lighting mast is visible; between two of these a delta (triangle) with a perimeter of 90 m was mounted. The second photo is a magnetic frame, located horizontally at a distance of 80 cm from the iron roof of the oil workers' trailer.

February 2001, tests again. Roof of the school. Antenna with a radiator diameter of 4 m. The first antenna ordered in production. I conducted experiments on the air, both in distance and in comparison with other types of antennas, so I was “popular” on the air and many radio amateurs gladly came to watch and take part in this process. By the way, on the main site, in the guest book there is a review from one of the radio amateurs.

June 2001, tests of the receiving antenna, I wrote about it, made of a copper tube and upside down (conder at the bottom, vacuum).

July 2001, at one of the objects (there is also a typo on the photo caption, not 2000, but 2001).

August 2001. Received antenna AMA-5, from DK5CZ. Nearby, it was made in Russia with a diameter of 1.7 m (you can see the bolts on the emitter, at the junction of the segments) and “horizontally” located with a diameter of 4 m (an improved, or rather improved, model).

June 2002. Lake Pleshcheyevo, a meeting of radio amateurs in the central part of Russia. They brought an antenna with a radiator diameter of 4 m, installed it near the tent and compared it with all the ones the members of the meeting had (and there were dipoles and J-antennas, and triangles).

July 2002. Northern Dvina River. Initially, they brought an antenna with a radiator diameter of 4 m, but later replaced it with an antenna with a radiator diameter of 1.7 m. The reason was that they did not pass in height under the bridges.

In September, tests were carried out with an antenna with a radiator diameter of 1.7 m on the tugboat "Limenda Komsomolets" (Limenda is a river flowing into the Northern Dvina) near the city of Kotlas.

Variable capacitors. The first photo is from the AMA-5 antenna, the rest are ours.

Automatic tuners were made - more precisely, a program was written for a single-chip processor, the commands of which control the electric motor - turning the capacitor.

A book by engineer S.I. appeared. Shaposhnikov “Radio reception and radio receivers” from the series Radio Amateur Library, published by the Nizhny Novgorod Radio Laboratory named after. IN AND. Lenin, 1924.

This book has a section on antennas, I will reprint it and post a scan of the drawing.

"Reception without antennas"

Section "Reception without antennas"

Reception for frames. If on the wooden frame shown in Fig. 27a, wind a certain number of turns of insulated wire, to the ends of which attach a variable capacitor C, you will get a closed oscillatory circuit that can oscillate in a wave, the length of which depends on the capacitance C and the self-inductance L of the frame. Such a contour, located in a vertical plane and called a receiving frame, has the following properties:

1. The magnetic lines of the electromagnetic wave, crossing the vertical parts of the turns, induce forced oscillations in the frame, to which the frame’s own wave can be tuned with capacitor C. If a detector circuit is connected to capacitor C, then the operation of transmitters can be received on such a frame.
2. The frame has a guiding effect, i.e. being installed as shown in Fig. 27, and tuned to the incoming wave, it best receives signals in the directions indicated by arrows 1 and 2, i.e. wave arriving in the plane of the frame, and does not receive waves arriving in directions 3 and 4 at all, i.e. waves arriving perpendicular to the plane of the frame. Thus, by placing the frame in a certain direction in which the loudest sound is obtained, we can determine in which direction from it the transmitting station is located.

Frames have their own advantages and disadvantages. The first include their lightweight device, small size, allowing them to be installed at home, their directing action, etc. Their main disadvantage is that they perceive too little energy, so the detector can only receive them over short distances. However, when working with good amplifier powerful transmitters are received through frames over thousands of miles.

Here are some frame sizes that are considered the most advantageous. The frame is square, with a side = 70 cm. For a wave of 300 m, 4 turns are placed; 600 m - 7 turns; 800 m - 10 turns; 1200 m - 14 turns; 1600 m - 20 turns; 2500 m - 40 turns, etc. Coil from coil is laid at a distance of one centimeter. The capacitance of capacitor C should be about 1000 pF.

Frames can be of various sizes and shapes. The most practical is considered to be a diamond-shaped frame placed on a corner, Fig. 27th century

(Links to information from the Internet)

• Magnetic Loop Antennas - by PY1AHD (a superb loop site!) Brazil.
• Stealth ST-940B Mobile HF NVIS Magnetic Loop Antenna - by Stealth Telecom. United Arab Emirates.
• HF LOOP AND HALF-LOOP ANTENNAS - by STAREC. France.
• PA3CQR Magnetic loop antenna page - by PA3CQR. Netherlands.
• 80m Frame Antenna - by SM0VPO. Sweden.

Magnetic loop home antenna – great alternative classic outdoor. Such designs allow transmitting signals up to 80 m. Coaxial cable is most often used for their manufacture.

Classic magnetic version loop antenna

Frame magnetic installation is a subtype of small-sized amateur antennas that can be installed at any point settlement. Under the same conditions, the frames show more stable results than their analogues.

In home practice, they use the most successful models from popular manufacturers. Most of the circuits are given in amateur literature for radio engineers.

Magnetic loop antenna made from coaxial cable indoors

DIY antenna assembly

Materials for production

The main element is a coaxial cable of several types, 12 m and 4 m long. To build a working model, you also need wooden planks, a 100 pF capacitor and a coaxial connector.

Assembly

A magnetic loop antenna is constructed without special training or knowledge of technical literature. By following the assembly order, you can get a working device the first time:

• connect wooden planks with a cross;
• cut grooves in the boards with a depth corresponding to the radius of the conductor;
• Drill holes on the slats at the base of the cross to secure the cable. Cut three grooves between them.

Precise sizing allows you to build a structure with high radio frequency reception.

Shape of magnetic frames

A magnetic antenna made of coaxial cable is a loop of conductor that is connected to a capacitor. The loop usually looks like a circle. This is due to the fact that this shape increases the efficiency of the design. The area of ​​this figure is largest compared to the area of ​​other geometric bodies, therefore, the signal coverage will be increased. Manufacturers of goods for radio amateurs produce round frames.

Installation of the structure on the balcony

To ensure that devices operate on a specific wavelength range, loops of various diameters are constructed.

There are also models in the form of triangles, squares and polygons. The use of such structures is determined in each specific case various factors: location of the device in the room, compactness, etc.

Round and square frames are considered single-turn, because the conductor is not twisted. To date special programs type KI6GD allow you to calculate the characteristics of only single-turn antennas. This type has proven itself well for working in high-frequency ranges. Their main disadvantage is their large size. Many specialists aspire to work for low frequencies, that's why magnetic frame installation is so popular.

Comparative calculations of several circuits with one, two or more turns, under similar operating conditions, showed the questionable effectiveness of multi-turn designs. Increasing the turns as much as possible is advisable solely to reduce the dimensions of the entire device. In addition, to implement this scheme, it is necessary to increase the cable consumption, therefore, the cost of homemade products increases unjustifiably.

Magnetic frame canvas

For maximum efficiency of the installation, one condition must be achieved: the loss resistance in the frame web must be comparable to the value of the radiation resistance of the entire structure. For thin copper tubes this condition is easily met. For large-diameter coaxial cables, this effect is more difficult to achieve due to the high resistance of the material. In practice, both types of structures are used, because other types work much worse.

Receiving frames

If the device performs exclusively the function of a receiver, then conventional capacitors with solid dielectrics can be used for its operation. To reduce the size, the receiving frames are made of multi-turns (made of thin wire).

Such designs are not suitable for transmitting devices, because The action of the transmitter will work to heat the installation.

Coaxial cable braid

The braided magnetic frame provides greater efficiency than copper tubes and a thicker conductor diameter. Models with a black plastic shell are not suitable for home experiments, because... it contains a large amount of soot. During operation, metal parts, when the shell is heated, emit chemical compounds harmful to humans. In addition, this feature reduces the transmission signal.

Coaxial cable SAT-50M made in Italy

This type of coaxial cable is only suitable for large antennas because... their conductor radiation resistance completely compensates for the input resistance.

Impact of external factors

Thanks to physical properties coaxial cables, antennas are not affected by temperature and precipitation. Only the shell created by external factors - rain, snow, ice - is susceptible to negative consequences. water has large losses compared to cable high frequencies. As practice shows, such structures can be used on balconies for several decades. Even in severe frosts there is no significant deterioration in reception.

To increase reception, it is better to place magnetic devices made from coaxial cable in rooms or places with reduced exposure to precipitation: under roof canopies, on protected parts of open balconies. Otherwise, the device will work primarily on heating environment, and only then to receive and transmit signals.

The main condition for stable operation is to protect the capacitor from external influences– mechanical, weather, etc. With prolonged exposure to external factors, due to high-frequency voltage, an arc may form, which, if overheated, quickly leads to desoldering from the circuit or failure of this part.

The frames for high-frequency ranges are horizontal. For low frequencies, at a height of more than 30 m, it is advisable to construct vertical structures. For them, the installation height does not affect the quality of reception.

Device location

If this mechanism will be located on the roof, then one condition must be provided - this antenna must be higher than all the others. In practice, achieving ideal placement is often impossible. The magnetic frame installation is quite unpretentious to the close proximity of third-party objects and structures - ventilation towers, etc.

The correct location would be on the roof with the core in the distance so that there is no signal absorption big models. In view of this, when installed on a balcony, its efficiency decreases. This arrangement is justified in cases where conventional receivers do not work correctly.

Frame and cable synchronization

Matching of parts is achieved by placing a small inductive loop into a large one. For symmetrical communication, a special balun transformer is included in the device. For asymmetrical - connect the cable directly. The antenna is grounded at the point where the cable is attached to the base of the large circle. Deformation of the cable helps to achieve more precise adjustment of the device.

Modification of a coaxial cable device

Pros and cons of the device

Advantages

• low cost;
• ease of installation and maintenance;
• availability of raw materials;
• installation in small rooms;
• durability of the device;
• effective operation near other radio devices;
• no special requirements to achieve high-quality reception (such devices operate stably both in summer and winter).

Flaws

The main disadvantage is the constant adjustment of capacitors when changing the operating range. The level of interference is reduced by rotating the structure, which can be extremely difficult during operation due to the geometric shapes and arrangement of the wooden planks. Due to radiation at close range, information is transferred from magnetic tapes (when the tape recorder is turned on) to devices with inductors (TVs, radios, etc.) even when the antennas are turned off. The level of interference can be reduced by changing the location of the device.

During operation, do not touch metal parts; due to the strong heat, you may get burns.

We do it ourselves. Video

You can learn how to make a broadband active antenna with your own hands from this video.

Magnetic loop antenna is the most appropriate budget solution For home use. The main advantages are working for different frequencies, ease of assembly and compactness. A well-made device can receive and transmit an excellent signal over a fairly long distance.

The ring is the most effective and common design of a loop antenna, since compared to other geometric shapes it covers the largest area with equal perimeters. An octagon is very close to a ring in terms of efficiency, while a square or rhombus is characterized by lower efficiency.

Typically, a variable trimmer capacitor is placed at the top of a vertically mounted ring, which is grounded at the lower opposite point for lightning protection.

For ease of settings, in some versions of the antenna the capacitor is mounted at the bottom of the ring and often in the housing along with the matching device.

Remote control of a variable tuning capacitor is not difficult, and therefore in stationary ring antennas the tuning capacitors are placed in the upper part of the ring. They also cope with galvanic coupling with ease.

One of the solutions is presented in the figure above in the form of a T-matching followed by a balun transformer.

The single-ended version with gamma matching looks like this:

In both cases, the length of the segment L, in gamma matching, should be about 0.1 of the circumference of the ring, and the distance y should be about λ/200.

Inductive coupling and matching are also widely used due to their ease of implementation.

The most commonly used option is this type:

A small inductive loop with a diameter ratio of 5:1 is placed inside the large loop. Thanks to balanced coupling, 50 ohm coaxial cable can be connected via a 1:1 ring core balun.

In an asymmetrical connection, the coaxial cable is connected directly as in the figure above (b).
An electrically feasible method of inductive coupling is shown in Figure (c). Shown here is only the connecting turn of the coaxial cable with a break
his screen in the middle of a turn. The screen of part of the right half of the cable is soldered to the base of the large ring, and at this point the antenna is grounded. By slightly deforming the coaxial cable cable, we achieve fine tuning antennas to minimum SWR. It is believed that the diameter d should be smaller, the higher the operating quality factor of the antenna.