What is the size of the magnetic loop antenna communication loop. Magnetic loop antennas. Magnetic loop antenna design

Experiments with magnetic loop antennas

Alexander Grachev UA6AGW

Last year I came across a 6-meter piece of coaxial cable. Its exact name: “Coaxial cable 1″ flexible LCFS 114-50 JA, RFS (15239211).” It has a very light weight, instead of an outer braid there is a solid corrugated pipe made of oxygen-free copper with a diameter of about 25 mm, the central conductor is a copper tube
about 9 mm in diameter (see photo). This is what prompted me to start building loop antenna. This is what I want to talk about.

The first antenna was built according to the DF9IV design. With a diameter of about 2 m and the same length of the power loop, made of coaxial cable, it worked very well for reception, but frankly poorly for transmission, the SWR reached 5-6.
The reception operating band (at a level of –6 dB) is about 10 kHz. At the same time, it perfectly suppressed electrical interference; with a certain orientation in space, the suppression of the interfering station was easily more than 20 dB.

After some thought, I came to the conclusion that the reason for the high SWR is the use of an internal conductor with its relatively small diameter by the exciting element. It was decided not to use the internal conductor at all, leaving it in the form of an open loop.

The tuning capacitor was soldered to the external screen. The receiving characteristics changed slightly, the minimum in the diagram became less pronounced, and the influence of surrounding objects became noticeable. But little has changed for the transmission. Then, after reading Grigorov’s article once again, it was decided to remove the outer braid from the frame cable and coat the copper in two layers with “HB” varnish (no more suitable one was found, however, it protects the copper well from
oxidation). And then, finally, the first positive results appeared. The SWR decreased to 1.5, about 20 local connections. The antenna was at a height of 1.5 m and could rotate in a vertical plane.

For comparison, we used a dipole with a total length of 42.5 m, made of a field wire with a symmetrical power line from a telephone “noodle” about 20 m long (a sort of antenna of a “beggar radio amateur”), located on the roof of a 5-story building at a height of about 3- x meters. It operated on 40 and 80 meters, powered via symmetrical matching device– SWR on both bands = 1.0. Unfortunately, the antennas were in different QTHs and there was no
opportunities to make direct comparisons. But the experience of using the dipole for a year made it possible to judge the effectiveness of the frame to a first approximation.

Now about the results: 1) SWR is about 1.5. 2) All correspondents noted a decrease (from 1 to 2 points) in the level of my signal, compared to the level with which they usually hear me on a dipole.

The rains that had begun by this time (as they say: “every other day, every day”) made further antenna experiments impossible. The main reason for the impossibility of further testing was the constant breakdown of the tuning
condenser due to increased air humidity.

I tried, perhaps, all the options available to me, I used connecting only stator plates, connecting two KPIs in series, I used capacitors from a coaxial cable, high-voltage capacitors
- it all ended in one thing - a breakdown. The only thing I didn’t try was vacuum capacitors, which was stopped by their prohibitive cost.

And here the idea came to use a capacitance in relation to the outer shield of the unused inner conductor. An attempt to calculate the required cable length based on the known linear capacity of the cable did not lead to reliable results, so the method of gradual approximation was used.

It was a great pity to cut such a wonderful cable, but “hunting is worse than bondage.” Connection diagram in the figure. For power supply, a loop of coaxial cable 2 m long was used, according to the DF9IV scheme; the supply 50-ohm cable itself was 15 m long. It could be assumed that the total capacitance would be obtained in accordance with the formula of series-connected capacitors, but the tuning capacitor is, as it were, a continuation of its own cable capacity.
For tuning, a butterfly capacitor from VHF equipment was used.

The breakdowns completely stopped, the antenna retained all the basic parameters of the classic magnetic loop antenna, but became single-band.

The main results are as follows: 1) SWR of the order of 1.5 (depending on the length and shape of the supply loop). 2) The magnetic antenna is noticeably inferior to the dipole (described above) with a comparable suspension height. The experiments were carried out in the 80 m range.

I was prompted to engage in further experiments with magnetic antennas by an article by K. Rothhammel in the second volume of his book, dedicated to magnetic frames, and an article by Vladimir Timofeevich Polyakov on a frame-beam or real EH antenna, and for understanding the processes occurring in antennas and around them, it turned out to be very useful article about the near field of antennas.

After reading the article about the frame-beam antenna, I came up with several promising projects, but currently only one has been tested, and this is what we will talk about. The antenna circuit is shown in the figure, appearance- on the picture:

All the experiments listed below were carried out in the 40m range. In the first experiments, the antenna was at a height of 1.5 m from the ground. Tried various ways connecting the “dipole” (capacitive) part of the antenna to the frame, but the one shown in the figure seemed optimal to me. Here, an attempt has been made to retrofit a magnetic frame, which emits predominantly a magnetic component, with elements that emit mainly an electrical component.

You can look at the same antenna differently: a coil connected to the middle of the dipole, as it were, extends it to the required dimensions, and at the same time, the beams connected in parallel to the tuning capacitor have their own capacitance (at specified sizes about 30 - 40 pF) and are included in the total capacitance of the tuning capacitor.

The circuit formed by the internal conductor and capacitor, in addition to increasing the signal level at reception approximately twice, apparently shifts the phase of the current of the frame itself, and provides the necessary phase matching (an attempt to turn it off leads to an increase in the SWR to 10 or more). Perhaps my theoretical reasoning is not entirely correct, but as further experiments have shown, the antenna works in this configuration.

Even during the very first experiments, an interesting effect was noticed - if, with the dipole part stationary, you turn
frame by 90 degrees - the reception signal level drops by approximately 10 - 15 dB, and by 180 degrees - reception drops almost to zero. Although it would be logical to assume that when rotated 90 degrees, the radiation patterns of the “dipole” part and the frame will coincide, but apparently not everything is so simple.

An intermediate version of the antenna was made, capable of rotating around its axis, in order to determine the radiation pattern; it turned out to be the same as that of the classic frame. The antenna was powered by the same communication loop as in the first experiments. Currently, the antenna is raised to a height of 3 meters, the rays run parallel to the ground.

About the results:

1) SWR = 1.0 at a frequency of 7050 kHz, 1.5 at 7000 kHz, 1.1 at 7100 kHz.
2) The antenna does not require range tuning. Using the transceiver's P-circuit capacitors, some adjustment of the antenna is possible if necessary.
3) The antenna is very compact.

At a distance of up to 1000 km, the frame and dipole have approximately the same efficiency, and at a distance of more than 1000 km, the frame works noticeably better than the wave dipole at the same suspension height, while the frame is four times
less than a dipole. The radiation pattern is close to circular, the minima are barely noticeable. About a hundred connections were made with 1;2;3;4;5;6;7;9 regions of the former USSR.

An interesting effect was noted - the estimate of the signal strength in most cases remained approximately the same, and at a distance to the correspondent of 300 km and 3000 km, this was not observed on the dipole. The reaction of the operators is interesting,
When I told you what I was working on, I was amazed that it was possible to work on this! All experiments were carried out on a homemade SDR transceiver with an output power of 100 W.

Material taken from the magazine CQ-QRP#27

A magnetic loop home antenna is an excellent alternative to classic outdoor ones. Such designs allow transmitting signals up to 80 m. Coaxial cable is most often used for their manufacture.

Classic version of a magnetic loop antenna

Frame magnetic installation is a subtype of small-sized amateur antennas that can be installed anywhere in a populated area. 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 manufacturing

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 designs is determined in each specific case by various factors: the 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

Due to the physical properties of 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 larger losses at high frequencies compared to cable. 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 to heat the 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 is 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 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 operation at different frequencies, ease of assembly and compactness. A well-made device can receive and transmit an excellent signal over a fairly long distance.

The good results obtained with the Magnetic Loop antenna prompted I1ARZ to try to build an antenna for the low frequency bands. He initially intended to build a circular loop antenna (Fig. 1) with a perimeter of about 10.5 m, which is a quarter of the wavelength at 7 MHz. For this purpose, a loop was made from a copper tube with a diameter of 40 mm with thin walls. However, during the work it became clear that bending and unbending tubes of this size is quite difficult, and the shape of the antenna was changed from round to square. Some reduction in efficiency is compensated by a significant simplification of manufacturing.

For the range of 1.8...7.2 MHz, you can use a copper tube with a diameter of 25...40 mm. You can also use duralumin tubes, but not everyone has the ability to weld in argon. After assembly, the entire antenna frame is covered with several layers of protective varnish.

The tuning capacitor is very important for proper operation of the antenna. He must be good quality, with a large gap between the plates. A vacuum capacitor with a capacity of 7...1000 pF with a permissible voltage of 7 kV is used. It can withstand power in the antenna of more than 100 W, which is quite enough. In the case where the 160 m range is used, the capacitance should reach 1600 pF.

A square-shaped loop is assembled from four copper tubes 2.5 m long and 40 mm in diameter. The tubes are connected together using four copper water pipes. The tubes are welded to the elbows. Opposite sides of the frame should be parallel to each other. A piece 100 mm long is cut out in the middle of the upper tube, a Teflon spindle is inserted into the cutout and secured on both sides with clamps and screws. The diagonal of the loop is 3.4 m, the total length is 10.67 m (together with copper plates 50 mm wide, to which the ends of the tube are attached, providing connection to the tuning capacitor). To ensure reliable contact, the plates must be welded to the ends of the tube after they are attached.

Figure 2 shows the design of the frame along with the base and supporting mast. The mast must be dielectric, for example made from a fiberglass rod. You can also use a plastic tube. At the bottom, the frame is fixed to the supporting mast with steel clamps (Fig. 3).

To strengthen the lower horizontal piece of the frame, a heated copper tube of slightly larger diameter is stretched over it over a length of approximately 300 mm. The motor that rotates the capacitor is mounted on a steel pipe at a height above the roof of about 2 m. To give rigidity to the entire structure, at least three guy wires are installed below the motor.

The easiest way to match the antenna frame and power line is with a coil of coaxial cable type RG8 or RG213. The diameter of the coil is determined empirically (about 0.5 m). Connection of the internal core and cable sheath is carried out in accordance with Fig. 4

After the matching coil is set to the lowest SWR, a corrugated plastic tube is pulled over the connection point to protect it from precipitation. A coaxial connector must be installed at the end of the matching coil. In the place of the lower fastening of the matching turn, a piece of copper tape is threaded under the duralumin mounting clamp, which, after bending, is soldered to the shielding sheath of the cable. It is needed for good electrical contact with a grounded duralumin tube (Fig. 5). In the upper part, the matching coil is attached to the dielectric mast with rubber clamps.

If the antenna is located on the roof, for remote control tuning capacitor required motor drive unit direct current. For this purpose, any small tape motor with a small gearbox is suitable. The motor is connected to the capacitor axis by an insulating clutch or a plastic gear. The capacitor axis must also be mechanically connected to a 22 kOhm potentiometer of group A. Using this potentiometer at the bottom, the position of the tuning capacitor is determined. The complete diagram of the control unit is shown in Fig. 6.

Naturally, the potentiometer must be located on the same side as the motor, connecting them with two plastic gears or a friction gear. The entire tuning unit is housed in a hermetically sealed plastic case (or tube). The cable to the motor and the wires from the potentiometer are laid along the fiberglass support mast. If the antenna is located close to the radio station (for example, on a balcony), tuning can be done directly using a long roller on an insulated handle.

Tuning capacitor placement

As already mentioned, the fixed and movable parts of the tuning capacitor are connected to the upper, cut part of the frame using two copper plates about 0.5 mm thick, 50 mm wide and 300 mm long each. The tuning capacitor is placed in a plastic tube, which is attached to a vertical fiberglass support mast (Fig. 7). The top of the frame is connected with a Teflon spindle and secured to the supporting fiberglass post using U-bolts.

Settings

Set the TRX to the equivalent load, switch the TRX output to the antenna. Do not use the antenna tuner in this experiment. With reduced output power, start rotating the capacitor until you obtain a minimum SWR. If you cannot achieve a low SWR in this way, try to slightly deform the matching coil. If the SWR does not improve, the turn must be either lengthened or shortened. With a little patience, you can achieve an SWR of 1... 1.5 in the ranges of 1.8...7 MHz. The following SWR values ​​have been achieved: 1.5 at 40 m, 1.2 at 80 m and 1.1 at 160 m.

results

The antenna tuning is very “sharp”. In the range of 160 m, the antenna bandwidth is a few kilohertz. The radiation pattern (DP) is almost circular. Figure 8 shows patterns in the horizontal plane for various vertical radiation angles.

The antenna gives the best results in the range of 40 m. With a power of 50 W, the author established many connections with the east coast of the USA with a report of 59. At distances of up to 500 km during the day, the reports were 59+20...25 dB. The antenna is also very good at reception, since a fairly “sharp” setting reduces the noise and signals of strong stations operating nearby. The antenna works surprisingly well in the range of 160 m. From the first attempts, communication was established at a distance of over 500 km with a report of 59 + 20 dB. From a fundamental point of view, in this range the antenna efficiency is much lower than in the 40 m range (see table).

Concluding remarks

• The antenna should be placed as far as possible from large metal objects such as fences, metal poles, drainpipes, etc.
• It is not recommended to place the antenna indoors, since the antenna frame emits a strong magnetic field during transmission, which is harmful to health.
• When working with powers above 100 W, the frame heats up under the influence of high current.
• At the highest range, the polarization of the antenna is horizontal.

The table above shows the main electrical parameters antennas in the specified ranges. A similar antenna can be built for higher frequency ranges, correspondingly reducing the size of the frame and the capacitance of the tuning capacitor.

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

• 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

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, the brought energy-saving lamp glowed almost at full strength.

The frequency range 1-30 MHz is traditionally called shortwave. On short waves you can receive radio stations located thousands of kilometers away.

Which antenna to choose for shortwave reception

No matter which antenna you choose, it is best for it to be external(outdoor), highest positioned and away from power lines and metal roofs (to reduce interference).

Why is the outdoor one better than the indoor one? In a modern apartment and apartment building There are many sources of electromagnetic fields that are such a strong source of interference that the receiver often receives only interference. Naturally, the external one (even on the balcony) will be less susceptible to these interferences. In addition, reinforced concrete buildings shield radio waves, and therefore the useful signal indoors will be weaker.

Always use coaxial cable to connect the antenna to the receiver, this will also reduce the level of interference.

Receiving antenna type

In fact, on the HF band the type of receiving antenna is not so critical. Usually a 10-30 meter long wire is sufficient, and a coaxial cable can be connected at any convenient location on the antenna, although to ensure greater broadband (multi-band), it is better to connect the cable closer to the middle of the wire (you will get a T-antenna with shielded reduction). In this case, the braid of the coaxial cable is not connected to the antenna.

Wire antennas

Although more long antennas can receive more signals, they will also receive more interference. This somewhat equalizes them with short antennas. In addition, long antennas overload ("phantom" signals appear throughout the entire range, the so-called intermodulation) household and portable radios with strong signals from radio stations, because they are small compared to amateur or professional radios. In this case, you need to turn on the attenuator in the radio receiver (set the switch to the LOCAL position).

If you are using a long wire and connecting to the end of the antenna, it would be better to use a 9:1 matching transformer (balun) to connect the coaxial cable, because The “long wire” has a high active resistance (about 500 Ohms) and such matching reduces losses on the reflected signal.

Matching transformer WR LWA-0130, ratio 9:1

Active antenna

If you don't have the ability to hang external antenna, then you can use an active antenna. Active antenna- this is, as a rule, a device that combines a loop antenna (either ferrite or telescopic), a broadband low-noise high-frequency amplifier and a preselector (a good active HF antenna costs over 5,000 rubles, although for household radios there is no point in purchasing an expensive one, something will do just fine like Degen DE31MS). To reduce interference from the network, it is better to choose an active antenna that runs on batteries.

The point of an active antenna is to suppress interference as much as possible and amplify the desired signal at the RF (radio frequency) level without resorting to conversion.

In addition to the active antenna, you can use any indoor antenna that you can make (wire, frame or ferrite). In reinforced concrete houses, the indoor antenna should be located away from the electrical wiring, closer to the window (preferably on the balcony).

Magnetic antenna

Magnetic antennas (loop or ferrite), to one degree or another, under favorable circumstances, can reduce the level of “urban noise” (or rather, increase the “signal-to-noise” ratio) due to their directional properties. Moreover, the magnetic antenna does not receive the electrical component of the electromagnetic field, which also reduces the level of interference.

By the way, EXPERIMENT is the basis of amateur radio. External conditions play a significant role in the propagation of radio waves. What works well for one radio amateur may not work at all for another. The most visual experiment of radio wave propagation can be carried out with a decimeter television antenna. By rotating it around the vertical axis, you can see that the highest quality image does not always correspond to the direction towards the television center. This is due to the fact that radio waves, when propagating, are reflected and “mixed with others” (interference occurs) and the highest quality signal comes from the reflected wave, and not from the direct one.

Grounding

Don't forget about grounding(through the heating pipe). Do not ground to the protective conductor (PE) in the socket. Old tube radios especially “love” grounding.

Jokes

Anti-radio interference

In addition to this, to combat interference and overloads, you can use preselector(antenna tuner). Using this device can suppress out-of-band interference and strong signals to a certain extent.

Unfortunately, in the city all these tricks may not give the desired result. When you turn on the radio, you can only hear noise (as a rule, the noise is stronger in the low frequency ranges). Sometimes novice radio observers even suspect their radios of malfunction or unworthy performance. It's easy to check the receiver. Disconnect the antenna (fold the telescopic antenna or switch to an external one, but do not attach it) and read the S-meter reading. After this, extend the telescopic antenna or connect an external one. If the S-meter readings have increased significantly, then everything is in order with the radio receiver, and you are out of luck with the receiving location. If the interference level is close to 9 points or higher, normal reception will not be possible.

Finding and identifying the source of interference

Alas, the city is full of “broadband” interference. Many sources generate broad spectrum electromagnetic waves, like a spark discharge. Typical representatives: switching power supplies, brushed electric motors, cars, electric lighting networks, networks cable television and Internet, Wi-Fi routers, ADSL modems, industrial equipment and much more.

The easiest way to “search” for the source of interference is to examine the room using a pocket radio (no matter what range, DV-SV or HF, just not the FM range). Walking around the room, you can easily notice that in some places the receiver is noisier - this is the “localization location” of the interference source. Almost everything connected to the network (computers, energy-saving lamps, network wires, charging device etc.), as well as the electrical wiring itself.

It is in order to somehow reduce the harmful effects of urban interference that “super-duper” sophisticated radios and transceivers have become popular. A city radio amateur simply cannot work comfortably on household equipment that performs well “in the wild.” Greater selectivity and dynamics are required, and digital processing signal (DSP) allows you to “work wonders” (for example, suppress tonal interference) that are inaccessible to analog methods.

Of course, the best HF antenna is directional (wave channel, QUARD, traveling wave antennas, etc.). But let's be realistic. Building a directional antenna, even a simple one, is quite difficult and expensive.