Magnetic antenna from VA3LLZ from Toronto. Coaxial Cable Magnetic Antennas 27MHz Magnetic Loop Antenna

Hello!
Yesterday I had a couple of hours of free time. I decided to implement a long-standing 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 does not work badly!

Because people ask a lot about this antenna, I post 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 gas-cylinder equipment of a car), it is very convenient and inexpensive to use a gymnastic aluminum hoop
the diameter of the small frame is 22 cm (the material is a 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 just change)
range 2.5 - 18.3 MHz
so that the frame starts to receive 1.8 MHz, add a 2200 pF capacitor in parallel

The idea is not new. One of the options lies. This is a single 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. Tuning for low frequencies is sharp, for 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 connection of the second section - the lower limit is 2.5 MHz.
Particularly impressive was the work of the frame on the 7 MHz band. It turns out to be a perfect magnetic antenna for Degena.

finally video

What is not clear ask. de RN3KK

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

Added on 08/18/2014
There is no limit to surprise. I placed this antenna on the loggia of the 9th floor. In the 40m range, a lot of Japanese stations were heard (range to Japan 7500 km). On 80m, only one Japanese station was received on the same day. The antenna deserves attention. I could not even think that long-distance routes can be received on this magnetic antenna (magnetic frame) ..

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

Reduced magnetic loop antennas are relatively rarely used by Ham-radio radio amateurs. However, with their shortcomings, such as low efficiency and narrow bandwidth, they have a number of advantages. This is the possibility of spatial and frequency selection of the radio signal, i.e. orientation of the antenna according to the maximum of the useful signal or to the minimum of the interference signal. Selection of a useful signal by the method of frequency detuning, as well as its small geometric dimensions relative to the wavelength. Therefore, loop antennas are most widely used as receiving antennas for radio direction finders and broadcasting receivers operating in the ranges of long, medium and short waves.

Such antennas are used most often in field conditions, and can be tuned in range with a threefold change in frequency. The efficiency of the antenna depends on its geometric dimensions relative to the wavelength, see fig. one.

This antenna is also used as a transmitting antenna. With small frame sizes, the amplitude and phase of the oscillations of the current flowing in the frame are practically constant along the entire perimeter. The maximum radiation intensity corresponds to the plane of the frame. In the perpendicular plane of the frame, the radiation pattern has a sharp minimum, and the overall pattern of the loop antenna has the shape of a "figure eight".

Electric field strength E electromagnetic wave (V/m) at a distance d (??3) from transmitting loop antenna, is calculated by the formula:

where:
I - current in the frame (A); n - number of turns; d — distance (km);
S - frame area (sq.m.); ? — working wavelength (m);
cos? is the angle between the plane of the frame and the direction to the considered point.

EMF E , induced in reception loop antenna, is calculated by the formula:

where:
n - number of turns;
S - frame area;
E — electric field strength at the observed point;
cos? is the angle between the plane of the frame and the direction of wave arrival.

The figure-of-eight radiation pattern of the frame allows using its minimums of the diagram in order to tune it in space from closely spaced interference or unwanted radiation in a certain direction in the near zones up to 100 km.

The antenna device is classical, and is shown in fig. 2, it consists of an open oscillatory circuit in the form of a deployed inductance tuned by the capacitor C to resonance. According to DK5CZ, the bandwidth also increases three times with an increase in the tuning frequency and, at a level of 0.707, it has a bandwidth from 3 to 30 kHz. In the manufacture of the antenna, it is required to observe the ratio of the diameters of the radiating ring and the coupling coil D / d as 5/1, it is made of a coaxial cable, located in close proximity to the radiating ring on the opposite side of the capacitor, and looks like in Fig. 3.

Since a large current flows in the radiating frame, reaching tens of amperes, the frame in the frequency ranges of 1.8-30 MHz is made of a copper tube with a diameter of about 40-20 mm, and the resonance tuning capacitor should not have rubbing contacts. Its breakdown voltage should be 10 kV with input power up to 100 W. The diameter of the radiating element depends on the frequency range used and is calculated from the wavelength of the high-frequency part of the range λv, where the perimeter of the frame P = 0.25λv.

We expand the bandwidth of the frame and increase the efficiency

The only problem that occurs with all shortened loop antennas is narrowband. In the range of 180-160 m with an antenna quality factor of 200 ... 250, the bandwidth at the level of 0.707 will be about 6 kHz, which is a big drawback when tuning the frequency of the radio station. The restructuring of the antenna within the range can also be done discretely, using a relay and a set of capacitors of constant capacitance.

To expand the bandwidth of the loop antenna and improve its efficiency, you can use several similar antennas, which are located in such a way relative to each other that there is a magnetic connection between them. And this means that the frames should be parallel to each other. In this case, it is enough to power only one antenna, and the rest will expand the bandwidth of the entire system, and increase the signal level by about 3 dB. On fig. 4a shows the frequency response of a single loop antenna, in fig. 4b - frequency response of two (or several) such antennas.

The frames must have the same geometric and electrical parameters and are installed parallel to each other at a distance of no more than the diameter of the frame. The distance is determined by the required bandwidth without sacrificing additional gain. The communication loop is installed on any of the frames, so that the second one works independently. The loop antenna works even better if there are three of them, i.e. one in the middle, and two additional ones are placed at a distance of half the diameter of the frame on both sides in the same plane.

If the radio amateur has difficulty in rotating such a structure, then the goniometer principle can be used and the frames are placed perpendicularly. Then only the link loop needs to be rotated. You get almost a direction finder.

73! UA9LBG & Radio-Vector-Tyumen

Article 2. Magnetic antennas (magnetic loop):

Antenna is a device for emitting and/or receiving electromagnetic waves by direct conversion of electric current into radiation (during transmission) or radiation into electric current (during 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 panicle, for a tube receiver, using a balcony option. I inserted my piglet, and the article turned out.)

And so I'll try to write 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 "post office Alabino". Every day in the morning, I took the bus to Golitsino, took the train to the Fili platform, then took the metro to Nogin Square (now Kitay-Gorod). then on foot to Pokrovsky Boulevard, to 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 rule happened almost every week, and only on Fridays. One day we are sitting, sipping red and twisting the vernier handle, listening to the conversations of radio amateurs. An unusual structure on the windowsill attracted my attention, I ask you from Das, and Sasha says that this antenna is called a magnetic loop (Magnetic loop) and shows an article in the magazine Radio No. 7 for 1989, p. 90, in the section for abroad. In a word, this is the article that Sergey Kashechlebov cited in the discussion on the forum. I came home, begged a halohoop from a neighbor, and after two hours, I made the first radio contact on 40 meters with Peter, my antenna was mounted on a plank, the KPI was screwed to the halohoop (duralumin is not soldered). This was my first experience, after 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 left for testing. We took several types of antennas with us, these are traditional triangles made of an antenna cord, 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, braid in the form of a corrugation 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. After a certain time, we get in touch, test the passage, draw up a daily schedule for the passage. And suddenly everything was gone, there was only "white noise" on the air, and nothing else. They tell me on the phone from the base that there is a magnetic storm, and a break for an indefinite time. Out of boredom, I started clicking, switching antennas on amateur bands. What was my surprise when I heard radio amateurs working on 40 meters. I'm for the microphone and let's go. I asked all correspondents to listen to two more antennas, switched to "delta" and spiral-pin, and then ML, I did not hear anything on those antennas and they did not hear me either.

Later, I persuaded the commercial director to buy a couple of antennas in Germany, I wanted different sizes, but bought the same type. At that time, production was established there and Christian DK5CZ was engaged in this (God rest his soul, the key was silent). But people still continue his work. So let's get back here. The German design was not practical, the diameter of the emitter was 1.7 m, one-piece, inconvenient during transportation. In general, their own antenna was made, the emitter consisted of three segments, AD-30 material (I took a piece of German 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 block 3 amateur transmissions from the range (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 has been to our team probably noticed that in the immediate vicinity of the radio station (300-500 m) there are three power lines in a semicircle, one of them is 500 kV. So the chatter in our S-meter is always 8-9 points. And when I put ML horizontally (on pegs 1 m high) on the roof, using it as a receiving antenna, then .... 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. It 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 standings, on the 17th floor there are 2 Cushcraft 40_2CD elements, i.e. he sits at 40 m and that's it, but we have a complete plug. At 40 m, the S-meter rests against the opposite wall, and on other higher bends it is not better. This went on for several years. And what do you think. When we put ML on reception, it works at the beginning of the SSB segment, 7.045 MHz, and we are at the end, 7.087 MHz, we do not feel it, as if it is 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 town of Kotlas, at about 3.00 on 40 meters I hear ER4DX, Vasily, working for Latin America. He has an antenna in several elements and a "kind" assistant. I volunteered to join the group, and on 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 site DK5CZ everything is there. And there is a Magloop4 program that allows you to calculate magnetic frames that can be made in the form of a circle, triangle, square, but here is the link, test it yourself: Magloop4 simulation 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 variable from a tube radio receiver (tuned once to the middle of the range). And at the end of the article I will post a scan of the instructions for ML.

The answer of one of the users of ODLR. Inspired by the unprecedented academic material of Pavel, he remembered a sports equipment (gymnastic metal hoop) made by the famous Khrunichev rocket and space company and unnecessarily resting behind the sofa ... I decided to experiment in haste ... Within an hour of handicraft work, I made the antenna shown in the attached photos ... The shunt capacitor (0.01 microfarads) was selected according to the maximum and purity of a 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 the best! The concept is right! Very satisfied. Thanks Pavel! The topic has moved rapidly towards the exchange of concrete practical results....

My answer. Alexander. All this is good that you have done, but it seems to me that it will have the same effect if you put 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 (I think so). 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 did 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 an air gap at the place where the emitter was cut, then the perimeter of the emitter was equal to half the wavelength, by the way, this is also confirmed by the program.

P.S. My friend experimented with these antennas on the 145 MHz band, made a double antenna, i.e. two emitters located on the same traverse (Viewed from above, the design looks like two wheels on the same axle). Khashnik controlled. The result is oh-oh-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, this is my personal opinion that it is the antenna feeding 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 incisions.

User responses. Pavel, I visited you more than once, but I was not interested in antenna management, but in vain ... Enlighten the people, photos in the studio, please.

Since there was no digital camera in those days, I used a "soap box". By the way, I forgot. There was another experience of use. I defended my diploma at VIA just using antennas of this type, the diploma was classified as "secret", but I think that over the 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 "Victory Radio Expedition". April 2000, the roof of the school (which later became a testing ground). And this is the exit near Volokolamsk, to the monument to the soldiers-sappers (May 8-9, 2000) they worked as RP3AIW. This is just an antenna from a cable "on a cross".

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

February 2001, again testing. School roof. Antenna with a radiator diameter of 4 m. The first antenna ordered in production. On the air, I conducted experiments, both in terms of distance and in comparison with other types of antennas, therefore I was "popular" on the air and many radio amateurs came with pleasure to watch and take part in this process. By the way, on the main site, in the guest book, there is a review of one of the radio amateurs.

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

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

August 2001 Antenna AMA-5 received from DK5CZ. Nearby, 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 (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 members of the rally (and there were dipoles and J-antennas, and triangles).

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

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

Capacitors of variable capacity. The first photo is from the AMA-5 antenna, the rest are our production.

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

A book by engineer S.I. Shaposhnikov “Radio Reception and Radio Receivers” from the Radio Amateur Library series, edition of the Nizhny Novgorod Radio Laboratory named after. IN AND. Lenin, 1924.

There is a section about antennas in this book, I will reprint it and post a scan of the drawing.

"Reception without antennas"

section "Reception without antennas"

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

The magnetic lines of the electromagnetic wave, crossing the vertical parts of the turns, induce forced oscillations in the frame, to which the self-wave of the frame can be tuned by the capacitor C. If a detector circuit is connected to the capacitor C, then the work of transmitters can be received on such a frame.
The frame has a guiding effect, i.e. when installed as shown in Fig. 27, and is 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 setting the frame in a certain direction, in which the loudest sound is obtained, we can determine in which direction the transmitting station is located from it.

Frames have their own advantages and disadvantages. The former include their light device, small size, allowing them to be installed at home, guiding their action, etc. Their main drawback is that they perceive too little energy, so that the detector can only receive them over short distances. However, when working with a good amplifier, powerful transmitters are received through frames for 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. A coil from a coil is stacked at a distance of one centimeter. The capacitance of the capacitor C should be about 1000 pF.

Frames can be of various sizes and shapes. The most practical is a diamond-shaped frame set at an angle, fig. 27th century

(Links to info from 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.

Because people ask a lot about this antenna, I post 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 gas-cylinder equipment of a car), it is very convenient and inexpensive to use a gymnastic aluminum hoop
the diameter of the small frame is 22 cm (the material is a 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 just change)
range 2.5 - 18.3 MHz
so that the frame starts to receive 1.8 MHz, add a 2200 pF capacitor in parallel

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

finally video

What is not clear ask. de RN3KK

Radio antennas help to significantly improve the sound quality, avoid interference, the original radio antenna can become an interesting element of the interior. Recently, magnetic-based designs have begun to appear and are in demand among radio amateurs. The frame magnetic antenna can be successfully replaced with outdoor devices for receiving radio signals with a range of 10 to 80 meters through the use of frames. They can be built anywhere in the city, as well as in a car, as an alternative to screwed to the body. Such antennas are very convenient and mobile, however, with a fairly simple design, their use has some features.

Loop magnetic antenna device

Conventional antennas, in addition to being firmly attached, must have a very decent mass, which is simply impossible to bring to mobile light radio reception devices. In modern conditions, a way out has been found - the required mass is simply imitated. This is done using a coaxial coaxial cable, which, with a length of half a radio wave, taken with a shortening factor, acts as an impedance amplifier.

The central conductor (or several) of such a cable is made of pure or tinned copper, which provides increased resistance to direct current, and also makes the cable flexible. The dielectric layer is made of foamed granulated polyethylene. These materials give the stability of the quality characteristics of the wire and a long service life. The shielding layer is a braid of copper or tinned wires. To improve the shielding properties, a second layer of braid is made over the laminated aluminum foil.

Modern magnetic antennas are improved variations of frame analogues. Such devices are coils on ferrite cores. Due to the increased magnetic permeability of this material, the magnetic field of electromagnetic waves in the coil circuits generates a very powerful flux, stronger than with no core.

Even small coils are capable of generating the same electromotive force as simple loop antennas, but with larger dimensions.

The dimensions of the cores are from 0.1 to 0.3 meters in length and from ½ to 1 sq. see cross-sectional area. Each coil, as a rule, has 2-3 dozen turns of copper wire.

Magnetic frames for a coaxial cable antenna are loops of conductive material attached to a capacitor. Most often there are loops of a round shape, since this way the device works much more efficiently. The area of a circle is smaller than the area of other geometric shapes, so the coverage of radio signals will be higher.

Note! In shops for radio amateurs, antenna frames are sold precisely in a round shape. However, there are also triangular, and square, and even polygonal frames, their use is explained by the peculiarities of the location in the house, the dimensions of the radio receiver, etc.

To receive a signal in the selected range, loops of different diameters are used.

Within the framework of both round and square shapes, an untwisted conductor is used (such antennas are called single-turn antennas), they function perfectly in the high frequency ranges, but at the same time their dimensions are quite large. These shortcomings are corrected by the magnetic frame design, which is gaining popularity among radio amateurs who prefer low frequencies, which is multi-turn.

Additional Information. The more turns, the smaller the dimensions of the antenna device.

Features of operation and location of the device

A loop magnetic antenna made of a coaxial cable is mainly used in cases where it is necessary to reduce the level of interference and noise from neighboring radio stations operating in a range close to the waves of the receiving device, but emitted in a different direction. Loop antennas are best at receiving radio waves propagating along its plane, but they do not catch signals that go in parallel at all. In order to achieve the best, without interference sounding of the desired radio station, you just need to rotate the frame around its axis.

Such mechanisms can be placed on the roof of the building. However, it must be taken into account that such antennas must be higher than others (therefore, when installed on a balcony, the efficiency decreases). At the same time, the operation of magnetic loop antenna devices is not affected by proximity to other objects and structures (ventilation towers, pipes, etc.).

Ideal positioning is almost impossible to achieve, however, it is best to mount the antenna so that the ferrite core is directed away, in which case the radio signal will not be jammed by larger antennas.

For normal operation of the loop antenna with a coaxial cable, it is necessary to synchronize the wire itself and the loops. Consistency can be achieved by placing induction small loops in large diameter ones. To make the structure work symmetrically, a balancing transformer device can be added to it. If radio symmetry is not required, the antenna cable can be connected directly.

For the antenna, it is necessary to provide grounding, it is made in the area where the loop is attached to the point where the base of the large loop is located.

Important! If the cable is slightly deformed, the antenna can be tuned more finely.

It is not recommended to shorten the coaxial cable during installation and further operation, therefore it is advisable to determine what length will be sufficient before purchasing the antenna.

Installing a magnetic loop antenna in a car seems to be a simple matter, but this manipulation must be carried out very carefully. Before placing the magnetic antenna on the body, it is necessary to clean the future installation site and the magnetic pad of the antenna from clogging, otherwise the car paintwork may be damaged.

Pros and cons of the device

Coaxial cable magnetic antennas have many advantages over other similar devices:

they are relatively easy to install, and in the future they do not require special maintenance during operation;
can be installed in small spaces;
the service life of such antennas is quite long;
availability and low cost of components, it can be assembled independently with initial knowledge and experience in radio engineering;
can function normally, being in the vicinity of other radio units, the use of a magnet as a component provides excellent clean reception in urban conditions;
stability of work does not depend on seasonal and weather conditions, no special efforts are required to achieve a clear reception of the radio signal;
magnetic-based car antennas are very mobile, i.e. you can install them in a few minutes and anywhere in the car (no drilling is required), which can make a noticeable touch to the exterior of the car (besides, you can put several antennas: in different places, which once again demonstrates the “coolness” of the car owner) ;
since the gain of the radio signal decreases sharply at wavelengths less than 1/10 of the length of the perimeter, the receiving magnetic antenna helps protect the radio from being overloaded by other radio stations;
in the VHF-FM range (frequency modulation, i.e. at frequencies of 65.9-74 megahertz), magnetic antennas demonstrate the highest quality reception, compared with analogues or even outdoor-type devices, while the frame perimeter is from 20 to 40 centimeters .

Magnetic antennas with coaxial cable are not without some disadvantages:

if you have to change the operating range of the radio, you need to constantly adjust the capacitors of variable capacitance for a clearer reception of the signal;
the easiest way to get rid of interference and extraneous terrestrial noise is by turning the antenna design around its own axis and at the same time changing its location, however, for frame magnetic devices, such manipulations are difficult due to the different shape of the frames and the inconvenient location of the wooden cable;
during signal transmission, the metal structural elements are very hot, which is fraught with burns if handled carelessly;
after installation, the length of the coaxial cable cannot be changed, because the reception may deteriorate significantly, which is due to a failure of the parameters in the oscillatory system of the radio receiver;
on a round or square frame there is an input electrical resistance of 120 ohms, while on the feeder it is 50 ohms, therefore, for matching, it is necessary to form a frame in the shape of a rectangle, where the short sides are half as long as the long ones, then the input resistance will also be 50 ohms, however, Structurally, it is rather complicated and inconvenient;
the more the real mass of the magnetic antenna is replaced by a coaxial wire, the lower the reception quality, so antennas of this type must be chosen very thoughtfully.

Do-it-yourself antenna assembly

Magnetic loop antennas have a fairly simple design, so they can be made even by not very experienced radio amateurs. Such an antenna can be assembled using a coaxial cable of any size.

To create the simplest instance of a magnetic antenna, the following constituent elements are required:

coaxial cable (coaxial) brand RG213, approximately 12 meters;
cable brand RG58, about 4 meters;
planks of dry wood, 2 by 4 cm in the amount of 4 pieces;
capacitance capacitor of 100 picofarads, 1 piece, while the interplate distance should not exceed 3 mm;
coaxial connector, one piece.

Mounting the parts of a homemade frame magnetic antenna is a fairly simple procedure. First, a cross is constructed from wooden slats, planks with sawn grooves are attached to it in the transverse direction. A loop is mounted on the cross to create resonance. It must consist of at least 4 turns of RG213 wire.

In addition, two holes are drilled in the cross bars located on the top, left and right, where the ends of the cable will be securely fixed. Three grooves must be cut between them. The dimensions of the cross base are not so important, but the side of the coax should be exactly 67 centimeters.

The frame must have the sum of the lengths of the sides, identical to 1/10 of the wave length of the lower FM range or the required shortwave frequency. However, if the radio signal is strong enough, then a perimeter equal to 1/10 of the wave length of the upper FM channel is acceptable.

If such a homemade antenna is planned to be used for a long period (both outdoors and indoors), it is best to take a cable made of technical copper with a foil braid (sometimes a tube polished to a shine is also suitable). Otherwise, over time, good radio reception cannot be expected.

For coloring, it is best to use paints containing metal oxides.

As for the magnetic frame, for the most efficient functioning of the structure, it is necessary that the losses in its web be adequate to the resistance of the entire system.

Magnetic loop antennas using coaxial cable are a modern and improved version of conventional loop antennas, which provide excellent radio reception mainly in the FM range and have increased mobility. You can assemble a completely working copy on your own without even undergoing special training.