Log-periodic television antenna. We make a television antenna with our own hands. To make it you will need to prepare

1. Do-it-yourself UHF television antenna

1. Ring-coaxial cable RK75, 530 mm long.
2. Loop-coaxial cable RK75, 175 mm long.
3. To the antenna.

Assembly:
To assemble this antenna, you don’t even have to go shopping.
To do this, you need to take an RK75 antenna cable 530 mm long (for the ring) and 175 mm long. (for loop).
Connect as shown in the figure.
Secure it to a sheet of plywood (plexiglass) using wire clamps.
Direct to telecentre.
Here is a UHF antenna that will work no worse than a purchased one.

2. Do-it-yourself UHF television antenna “Narodnaya”

The antenna is an aluminum disk with an outer diameter of 356mm and an inner diameter of 170mm. and 1mm thick, in which a 10mm wide cut was made.
A printed circuit board made of glass lite 1mm thick is installed in place of the cut. This board has two holes for mounting with M3 screws.
The leads of the matching transformer T1 are soldered to the printed circuit board attached to the antenna.
For a transformer, it is best to use a ring core with an outer diameter of 6...10mm and an inner diameter of 3...7mm. and thickness 2...3mm.
The transformer windings are covered with a single-layer insulated wire with a diameter of 0.2...0.25 mm. and have the same number of turns, from 2 to 3 turns. The length of the coil bends is 20mm.
With such a transformer, reception in the meter and decimeter range is possible at a distance of 25...30 km. At a distance of up to 50 km. The antenna works satisfactorily only on decimeter channels.
Without a transformer, the distance of reliable reception is halved.
However, there is a circuit that allows you to get similar results without a transformer; for this you need to assemble the following circuit:

3. Do-it-yourself log-periodic television antenna (UHF).

A. Mast
IN. Metal plate (dimensions 87x30x5)
WITH. metal tubes d 16…19mm
D. textolite plate (dimensions 87x30x5)
E. braid
F. coaxial cable
G. central core
7,6,5,4,3,2,1. vibrators

Assembly

1. Take two metal tubes 450 mm long and 16...19 mm in diameter.
2. Make two plates measuring 87x30x5mm. (one is made of metal, the other is made of textolite), drill holes in them, as shown in the pictures.
3. Secure the tubes in the plates (to the metal plate by soldering, and to the textolite plate using screws screwed from the ends of the plate with a diameter of 2.5 mm.
4. In metal tubes, along their length, at the distances indicated in the figure, drill holes with a diameter of 3.3 mm. and cut the M4 thread.
5. Screw 14 directors made from a rod with a diameter of 5 mm into the holes. At one end of each rod, cut an M4 thread to a length of 10mm.
The lengths of the directors, taking into account the part of the length of the threaded end, according to the vibrator number (see figure), are shown in the table:

Vibrator No.…..length in mm…..number of pieces
1…………………………..107………………..2
2…………………………..129………………..2
3…………………………..155………………..2
4…………………………..186………………..2
5…………………………..225………………..2
6…………………………..272………………..2
7…………………………..330………………..2

6. Place the coaxial cable in one of the tubes and solder it according to the figure. Paint the solder ends with paint.

7. Attach the antenna to the mast.

Antenna from user Evgen:
1. Take two EMPTY jars - for channels 21 to 41, 0.5 l is better, for channels 42 - 69 - 0.33 l.
2. Fasten them in any convenient way (electrical tape, adhesive tape, rope, glue, etc.) on a solid piece of dielectric (rail, stick, piece of plywood - it is better to paint or varnish the wood, textolite, getinax, etc.) onto at a distance of 10 - 15 mm from each other.
3. We make 2.5 - 4 mm holes in each jar along the edges (as many screws, washers, nuts can be found) and with the help of these we attach the central core of the cable to one jar, and the braid to the other. You can attach any balancing device, but you can do without it.
The receiving distance depends on the installation location of this design (outside is better) and the power of the transmitter.
The holes are on those edges where the jars are closer to each other. And it’s more convenient to first fasten the cable (and the balancing device - if you’re lazy), and then the jars to the supporting structure.

In Soviet times, it was not at all easy to purchase a ready-made and high-quality television antenna, so many craftsmen tried to make them themselves. They produced quite decent samples of antenna products that received a decimeter-length terrestrial signal relatively well (see the figure below).

Nowadays, everything has changed dramatically, and digital television has gradually begun to replace analogue. However, a high-quality UHF antenna that works normally in remote regions of the country still remains in demand among amateurs and professionals.

Modern digital television broadcasting

Advantages of the UHF range

In recent years, noticeable changes have been observed in the terrestrial television broadcasting sector, which have a certain impact on which UHF antenna is optimal for remote areas. It is especially important that today almost all television broadcasting is focused on the digital UHF range, to cover which the same decimeter antennas will be required.

One of the reasons why these frequencies are preferred is the well-known economic factor. The fact is that modern equipment of transmitting stations, as well as wave channels (feeders) and antennas, have become much cheaper. Let's add to this the reduction in maintenance costs for transmission systems and other station devices.

In addition, UHF antennas, complete with appropriate digital equipment, provide the following advantages:

• If you use a UHF antenna for personal purposes, you will be able to receive a signal even in places remote from the city limits that were previously considered inaccessible;
• In remote areas, range coverage is ensured by the power of transmitters without the need to use relay towers;
• Another advantage of receivers of this class is the low sensitivity of the digital UHF signal to interference.

Note! The digital signal has certain disadvantages, most often manifested when there are any mismatches in the transmitting path.

The consequence of this is the appearance of characteristic gaps in the image even if its quality is quite high. The cause of such violations can be noticeable phase distortions caused by deviations of the path characteristics from the norm.

Features of UHF antennas

A modern UHF antenna differs from its predecessors in that its individual qualities (primarily the amplifying effect) begin to come into first place. Therefore, it can be used at almost any (within line of sight) distance from the transmitting station. When using such an antenna, due to the processing of relatively weak signals in the amplifier, it is possible to achieve high image quality. The main parameters of the receiving and amplifying path are specified by the following technical requirements:

• Its amplitude-frequency response (AFC) should be as uniform as possible over the entire band of received frequencies (see the graph in the figure below);

• The presence of small dips and peaks on it should not lead to the appearance of phase distortions and discontinuities in the image;
• The electronic part of the receiving path must be coordinated with the feeder over the entire range of received frequencies.

If these conditions are met, the antenna for digital TV does not require additional devices to ensure its adaptation to local reception conditions.

Homemade antennas

Immediately before you make a decimeter antenna with your own hands, you should understand its existing types that are available for self-production.

According to the experience accumulated by radio amateurs, the following types of receiving devices fit into this category:

• The so-called all-wave antenna, the characteristics of which are practically independent of the frequency of the received signal;
• A special product with a log-periodic range, having nonlinear parameters;
• Z-type antenna (photo below).

The first of these products is particularly easy to manufacture; it can be used to receive a signal in suburban conditions (in the absence of strong interference). An all-wave indoor antenna also does an excellent job of processing an analog signal, but only if the station is not too far from the receiver.

Additional Information. Unlike devices of the type we are considering, a mv antenna, for example, due to the long wavelength of the received signal at home, is made with great difficulty.

Products with a log-periodic frequency response can also be classified as easy-to-manufacture options. They perfectly match the feed line in the range they cover and at the same time do not pass (filter) all third-party signals. Possessing average-level characteristics, such receiving structures have also proven themselves well in urban environments.

Zigzag, or Z-antennas, in the decimeter version look more miniature than in the meter version. They are much more efficient than all the samples considered and can be used even with relatively poor signal quality.

Important! It is possible to obtain ideal coordination with the feeder (to ensure the required symmetry) through the use of a special antenna design, in which certain dipole points are located in wave nodes with zero potential.

You can learn more about the design of such an antenna at https://remstroysam.ru/.

Homemade antenna parameters

Any decimeter antenna made at home with your own hands must first be calculated according to its permissible parameters and characteristics. Their exact description will require the performer to have knowledge of the basics of electrodynamics and higher mathematics, which is not at all necessary for a visual representation.

For this purpose, approximate but understandable definitions are sufficient (see the figure below).

The figure shows that the effective sensitivity zone of UHF antennas is represented in the form of multidirectional lobes, and their characteristics are expressed through the dimensions of the main, side and rear lobe formations.

With this approach, the following performance indicators are introduced:

• Gain is the ratio of the peak value of the signal induced in the antenna in the direction of the main lobe to the reference value for a circular half-wave dipole (CU);
• The coefficient of action in a certain direction is the ratio of the signal reception angle over the entire coverage area of ​​the antenna (360 degrees) to the same indicator for the main lobe (KND);
• Protection factor is the ratio of the energy incident on the antenna from the main direction to the same parameter for the side or rear lobe (SC).

Note! There are types of antennas in which the gain and directivity are in no way connected with each other (for example, special reconnaissance devices with a high degree of directionality, but low gain).

But there are also models (Z-antennas, in particular) in which low efficiency is combined with high gain.

Features of self-production

Before assembling a UHF antenna with your own hands, in all elements of which high-frequency currents of the useful signal circulate, you should familiarize yourself with the nuances of their assembly. The features of these procedures are expressed in the following requirements.

Firstly, all connections of the metal components of home-made products should be made only by soldering or welding.

Helpful explanation. The need for high-quality articulation of guides and dipoles is explained by the fact that in the open air, poor contacts are quickly destroyed and lead to a sharp weakening of the received signal.

Particular attention to the reliability of contact should be paid when forming nodes with zero field potential. According to theoretical calculations, peak current values ​​are observed in them, which ultimately determine the quality of operation of the receiving device. That is why these parts of the structure are made in the form of a bend made from a single piece of metal tube.

Secondly, before making an antenna, it is important to pay attention to the quality of the connection between its structure and the supply cable. The fact is that both the braid and the central core of modern coaxial cables are usually made not of copper, but of inexpensive alloys that are resistant to corrosion. At the same time, they are soldered with great difficulty, and if they are overheated, they can collapse. That is why to work with them, a soldering iron with a power of up to 40 watts and low-melting solder in combination with a paste-like flux should be used.

Note! During the soldering process, you should not save much on the paste, since under its influence the solder will immediately begin to spread over the braiding wires (under a layer of flux heated to a boiling state).

The third condition for obtaining a high-quality antenna is the need to carefully monitor the dimensions of the mounted dipoles and the order in which they appear in the line of beam guides. Next, we will consider the manufacturing procedure for antennas of each of the previously listed classes.

Manufacturing Features

There are many options for making such a product. To assemble the simplest of them, you will need the following quite accessible parts:

• Two metal plate blanks of a triangular shape;
• A pair of wooden slats selected according to the size of the structure;
• A set of copper wires coated with a layer of protective enamel (general view of the product and its diagram in the figure below).

For the normal operation of such an antenna, the diameter of the wires does not matter much; in this case, the distance between their extreme points is chosen to be approximately 20-30 mm. The gap between two metal plates with the mating ends of copper wires in insulation soldered to them is 10 mm.

Additional Information. Metal plates can be made in the form of a square made of fiberglass with a layer of copper foil on one side (sometimes regular triangles are cut out along the copper layer).

The width of the antenna obtained in this way will be equal to its height, and the full opening angle of the canvases will be 90 degrees. The procedure for laying the supply wire is shown in the same figure, and the point of the so-called “zero” potential is marked in yellow.

It is not at all necessary to solder the copper braid from the coaxial cable to the working surface (plate) - it is enough to tie it tightly to it, and the resulting container can be used as a matching one.

An all-wave antenna assembled in this way can be stretched in a window opening with a size of about 1.5 meters. It is capable of receiving signals in the band of meter and DCM waves from almost all directions. The main advantage of this design is that it is not required to rotate it in order to optimally tune to the transmitting station.

Its drawback is a small (almost single) KU and completely zero SDC, which excludes the possibility of using this homemade product outside areas of reliable reception.

Log-periodic antenna (LPA)

This type of antenna device is made in the form of a supporting base (it is called a collecting line), on which the halves of the receiving dipoles are alternately placed. The latter are pieces of wire with a length that is a multiple of one-fourth of the working wave, the dimensions and distance between which vary according to a log-periodic law (as indicated in the figure below).

The electrical circuit of such an antenna is quite simple, but calculating the parameters of its components will take too much time and space. For this reason, we direct anyone who wants to become more familiar with the procedure for its construction to the address already given above.

The only thing that should be noted when carrying out preparatory work is the need to choose one of the following options:

• A product with an already configured receiving line (with a short circuit at the end farthest from the cable connection);
• LPA with an untuned (free) beam base, which is preferred when receiving a digital signal.

The second option is also good because in this case the matching parameters with the cable (input impedance of the path, in particular) do not depend on frequency.

Z-type antenna

The zigzag design, or more simply “zigzag” (it is also called the Kharchenko antenna) belongs to the category of broadband signal receivers. In the UHF range, it can be made small in size and easily placed indoors.

This design is especially convenient in areas and settlements remote from the city, where there is often a need for reception from different directions. Its overlap coefficient of received frequencies is about 2.6-2.7. The Kharchenko antenna is quite complicated to make with your own hands, since it also requires a large amount of calculations.

Those wishing to familiarize themselves with its design in more detail are advised to pay attention to the sources indicated at the end of the review.

Additional Information. One of the varieties of the zigzag design is a rhombus, the main contour of which is made of copper tubes or aluminum strips 6 mm thick. The appearance of this variety is shown in the figure below.

Most often, this version of the UHF antenna is in demand when receiving a digital signal.

Wave channel antenna

The “YAGI” type design (translated from English as “wave channel antenna”) consists of a number of passive and active vibrators located along the emitter line parallel to one another. Its appearance can be seen in the following figure.

The supply television cable is connected only to active vibrators, as a result of which the wave impedance of the receiving path decreases due to mismatch. To maintain the gain at the desired level, active vibrators are made in the form of a loop with a resistance of about 300 Ohms. The total value of this parameter for the entire set of active and passive elements after a series of appropriate actions becomes equal to 75 Ohms, which satisfies the matching requirements.

To manufacture UHF wave channel vibrators, you will need about 16 metal tubes with a diameter of 6 to 10 mm. All these elements must be welded to the main boom of the emitter at points of zero potential. In this case, any material can be chosen as the base of the arrow-shaped guide, including polypropylene tubes.

Important! To obtain high gain, the design elements of such an antenna must be perfectly matched to the parameters of the supply cable.

As a natural matching element, it is allowed to take a loop cut from a piece of coaxial cable for a TV. Its calculated size is chosen equal to half the operating wavelength.

In the final part of the review, we note that there are other antenna options, different from those considered, the drawings and diagrams of which are quite suitable for self-assembly. But for each specific user, only those that correspond to his capabilities and level of training are suitable.

Video

So, imagine this situation: in the evening you decided to watch your favorite TV program, and suddenly the TV stopped showing. Or another case: You arrived at the dacha, have already prepared for a vacation, and again the same situation - not a single channel works. What to do in this case? The answer is simple - you need to make an antenna for the TV with your own hands, because most likely the cause of the breakdown is in this device. Next, we will look at the simplest creation options, which will require a minimum of available tools and time.

Idea #1 – Use beer cans!

This version of a homemade television antenna is the simplest and fastest to manufacture. The maximum number of channels that will be provided to you is 7, but this figure may vary slightly depending on the region.

To make a TV antenna from beer cans, you will need the following materials:

• 2 small screws, also called “bugs”;
• 2 prepared beer cans (empty, washed and dried);
• from 3 to 5 meters of television cable (can be taken from a failed device);
• soldering iron and tin (for better fixation of contacts), availability is optional;
• screwdriver;
• wooden trempel;
• electrical tape or tape.

Finding all the materials in the house will not be a problem, so having prepared them, we immediately get down to business.

In order to make a homemade antenna from cans, you need to complete the following steps:

1. We prepare the cable. First, at a distance of 10 cm from the edge, you need to make an incision and remove part of the top layer of insulation. Having opened access to the screen, we collapse it into one turn. After this, we cut off the middle insulating layer, exposing the thin copper core of the cable. As for the second end of the conductor, there should be a regular plug there.
2. We prepare the jars. There will also be no difficulties with containers that will act as signal receivers. First you need to choose the optimal dimensions of beer cans. It is better to use liter ones, but if these are not available, containers with a volume of 0.5 and 0.75 liters will do a good job.
3. Let's make contacts. At this stage, the twisted cable screen is attached to one can, and the copper core itself is attached to the other. Fixation is carried out with bedbugs using a screwdriver. In order to make the picture quality on the TV screen higher (signal transmission quality), it is recommended to fix the wire not only with clamps, but also with a soldering iron (tack a little). The result should look like this:
   
4. We assemble a homemade antenna for a TV. The signal receiver is ready, now we are making a supporting structure, which is the trempel. Using electrical tape, we fix the containers to the trempel (as shown in the photo). We draw your attention to the fact that the banks must be strictly on the same straight line, otherwise the homemade product will not work as we would like.
   
5. Setting up an antenna for the TV. Now you need to experiment with the optimal distance between the cans, as well as where to hang the device, so that the homemade product catches many channels. We turn on the TV and determine exactly how the receivers should be located and where is the most suitable place to work. This is where the creation technology ends.
   

As you can see, the whole process is quite simple and does not represent anything complicated. The optimal distance is 75 mm between the ends of the cans, and the best installation location is near the window. In individual cases, the distance between banks can be made larger or smaller.

Idea No. 2 – Use wire

Another equally good option that is advisable to use in the village is a homemade antenna made of copper wire with an amplifier.

All you need for production is:

• amplifier (suitable from an old device);
• two pieces of wire 180 cm each;
• a piece of metal (or wood) plate 15*15 cm;
• electric drill with a set of drills (or welding machine);
• small bolts;
• hammer;
• iron pipe;
• TV cable of suitable length.

So, to make your own TV antenna from copper wire, you need to complete the following steps:

Please note that in the photo examples, both the amplifier, the reflector, and the wire are covered with paint. Painting protects the structure from corrosion and other adverse factors, significantly extending the life of a homemade TV antenna.

Idea No. 3 – Home HDTV device

If the first 2 options worked at a frequency of no more than 270 MHz, then the next manufacturing method will allow you to enjoy a higher quality picture, because The signal range can reach up to 490 MHz. The only part that is unlikely to be found among household items is a matching transformer from 300 to 75 Ohms. You will need to buy it in advance if you decide to make your own TV antenna as an experiment and improve your skills. Although there are instructions for making a homemade transformer, you can find and use it.

Materials you will need:

1. Scotch
2. Cardboard
3. Stationery knife
4. Foil
5. Stapler
6. Scissors
7. Marker
8. Roulette

Having prepared all this school kit, let's get down to business!

First you need to sketch (or print on your computer) this diagram:

Now, according to the diagram, we cut out all the spare parts, including the necessary pieces of foil:

After this, you need to make a reflector with dimensions of 35 * 32.5 cm (height and width). Cover one side with foil.

In the middle we cut out two identical rectangles, which are necessary in order to completely assemble the signal catcher of a homemade antenna for a TV. The rectangle should be 3.5 cm long, its purpose is to maintain the distance between the reflector and the auxiliary parts.

We glue the parts onto the rectangle, and when the cardboard homemade product hardens, we drill holes for the television cable.

We connect the transformer and insert the cable into the plug. A more powerful TV antenna is ready for use! It should also be noted that this homemade version is only suitable for indoor use, because paper will quickly deteriorate outdoors.

Another option for a powerful device made at home:

Idea No. 4 – Apartment option

There is another way to make a powerful antenna for a TV from improvised materials, which is suitable for both outdoor and indoor use.

To make the device you will need the following materials and tools:

• 4-meter copper wire, cross-section 4 mm2;
• board of arbitrary thickness, 55 cm long and 7 cm wide;
• wood screws;
• ruler or tape measure;
• a simple pencil;
• screwdriver;
• soldering iron;
• plug

So, first, according to the drawing, we drill holes in the board:

Then we transfer the drawing data to the board and drill in the appropriate fastening points.

Next, the copper wire must be cut into 8 pieces of 37.5 cm each.

In the middle of each of the 37.5 cm sections, the insulation must be removed (as shown in the picture).

We cut off 2 more copper wire sections 22 cm long and roughly divide them into 3 equal parts, again removing the insulation at the inflection points.

We bend the prepared wire in exposed areas. We draw your attention to the fact that for those segments that are bent in half, the distance between the ends should be 7.5 cm (the optimal value for receiving a signal from a homemade television antenna).

Next, we attach the plug to the finished homemade product, and connect the television cable to it.

This completes the manufacturing process. We select a suitable location and install the device.

So we have provided the simplest instructions. We hope that now you know how to make a home TV antenna with your own hands! We draw your attention to the fact that today on the Internet you can find many other options in which inventors do without cans and wire. Among other available means, copper tubes, aluminum disks and electrodes are often used. The advantage of the options we have listed is that you can quickly make such antennas for a TV with your own hands, without spending the whole evening on it.

Related materials:

Visual video instructions for creating a simple antenna from cans

Assembling a digital antenna from a TV cable and a cardboard box

HDTV antenna made from improvised means

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Once upon a time, a good television antenna was in short supply; purchased ones did not differ in quality and durability, to put it mildly. Making an antenna for a “box” or “coffin” (an old tube TV) with your own hands was considered a sign of skill. Interest in homemade antennas continues to this day. There is nothing strange here: the conditions for TV reception have changed dramatically, and manufacturers, believing that there is and will not be anything significantly new in the theory of antennas, most often adapt electronics to long-known designs, without thinking about the fact that The main thing for any antenna is its interaction with the signal on the air.

What has changed on air?

Firstly, almost the entire volume of TV broadcasting is currently carried out in the UHF range. First of all, for economic reasons, it greatly simplifies and reduces the cost of the antenna-feeder system of transmitting stations, and, more importantly, the need for its regular maintenance by highly qualified specialists engaged in hard, harmful and dangerous work.

Second - TV transmitters now cover almost all more or less populated areas with their signal, and a developed communication network ensures the delivery of programs to the most remote corners. There, broadcasting in the habitable zone is provided by low-power, unattended transmitters.

Third, the conditions for the propagation of radio waves in cities have changed. On the UHF, industrial interference leaks in weakly, but reinforced concrete high-rise buildings are good mirrors for them, repeatedly reflecting the signal until it is completely attenuated in an area of ​​seemingly reliable reception.

Fourth - There are a lot of TV programs on air now, dozens and hundreds. How diverse and meaningful this set is is another question, but counting on receiving 1-2-3 channels is now pointless.

Finally, digital broadcasting has developed. The DVB T2 signal is a special thing. Where it still exceeds the noise even just a little, by 1.5-2 dB, the reception is excellent, as if nothing had happened. But a little further or to the side - no, it’s cut off. “Digital” is almost insensitive to interference, but if there is a mismatch with the cable or phase distortion anywhere in the path, from the camera to the tuner, the picture can crumble into squares even with a strong clean signal.

Antenna requirements

In accordance with the new reception conditions, the basic requirements for TV antennas have also changed:

• Its parameters such as the directivity coefficient (DAC) and the protective action coefficient (PAC) are now of no decisive importance: modern air is very dirty, and along the tiny side lobe of the directional pattern (DP), at least some interference will get through, and You need to fight it using electronic means.
• In return, the antenna's own gain (GA) becomes especially important. An antenna that catches the air well, rather than looking at it through a small hole, will provide a reserve of power for the received signal, allowing the electronics to clear it of noise and interference.
• A modern television antenna, with rare exceptions, must be a range antenna, i.e. its electrical parameters must be preserved naturally, at the level of theory, and not squeezed into acceptable limits through engineering tricks.
• The TV antenna must be matched with the cable over its entire operating frequency range without additional matching and balancing devices (MCD).
• The amplitude-frequency response of the antenna (AFC) should be as smooth as possible. Sharp surges and dips are certainly accompanied by phase distortions.

The last 3 points are determined by the requirements for receiving digital signals. Customized, i.e. Working theoretically at the same frequency, antennas can be “stretched” in frequency, for example. antennas of the “wave channel” type on the UHF with an acceptable signal-to-noise ratio capture channels 21-40. But their coordination with the feeder requires the use of USSs, which either strongly absorb the signal (ferrite) or spoil the phase response at the edges of the range (tuned). And such an antenna, which works perfectly on analogue, will receive “digital” poorly.

In this regard, from all the great variety of antennas, this article will consider TV antennas, available for self-production, of the following types:

1. Frequency independent (all-wave)– does not have high parameters, but is very simple and cheap, it can be done in literally an hour. Outside the city, where the airwaves are cleaner, it will be able to receive digital or a fairly powerful analogue not a short distance from the television center.
2. Range log-periodic. Figuratively speaking, it can be likened to a fishing trawl, which sorts the prey during fishing. It is also quite simple, fits perfectly with the feeder throughout its entire range, and does not change its parameters at all. The technical parameters are average, so it is more suitable for a summer residence, and in the city as a room.
3. Several modifications of the zigzag antenna, or Z-antennas. In the MV range, this is a very solid design that requires considerable skill and time. But on the UHF, due to the principle of geometric similarity (see below), it is so simplified and shrunk that it can well be used as a highly efficient indoor antenna under almost any reception conditions.

Note: The Z-antenna, to use the previous analogy, is a frequent flyer that scoops up everything in the water. As the air became littered, it fell out of use, but with the development of digital TV, it was once again on the high horse - throughout its entire range, it is just as perfectly coordinated and keeps the parameters as a “speech therapist.”

Precise matching and balancing of almost all antennas described below is achieved by laying the cable through the so-called. zero potential point. It has special requirements, which will be discussed in more detail below.

About vibrator antennas

In the frequency band of one analog channel, up to several dozen digital ones can be transmitted. And, as already said, the digital works with an insignificant signal-to-noise ratio. Therefore, in places very remote from the television center, where the signal of one or two channels barely reaches, the good old wave channel (AVK, wave channel antenna), from the class of vibrator antennas, can be used for receiving digital TV, so at the end we will devote a few lines and to her.

About satellite reception

There is no point in making a satellite dish yourself. You still need to buy a head and a tuner, and behind the external simplicity of the mirror lies a parabolic surface of oblique incidence, which not every industrial enterprise can produce with the required accuracy. The only thing homemade people can do is set up a satellite dish, about that.

About antenna parameters

Accurate determination of the antenna parameters mentioned above requires knowledge of higher mathematics and electrodynamics, but it is necessary to understand their meaning when starting to manufacture an antenna. Therefore, we will give somewhat rough, but still clarifying definitions (see figure on the right):

• KU - the ratio of the signal power received by the antenna on the main (main) lobe of its RP to its same power received in the same place and at the same frequency by an omnidirectional, circular, DP antenna.
• KND is the ratio of the solid angle of the entire sphere to the solid angle of the opening of the main lobe of the DN, assuming that its cross section is a circle. If the main petal has different sizes in different planes, you need to compare the area of ​​the sphere and its cross-sectional area of ​​the main petal.
• SCR is the ratio of the signal power received at the main lobe to the sum of the interference powers at the same frequency received by all secondary (back and side) lobes.

Notes:

1. If the antenna is a band antenna, the powers are calculated at the frequency of the useful signal.
2. Since there are no completely omnidirectional antennas, a half-wave linear dipole oriented in the direction of the electric field vector (according to its polarization) is taken as such. Its QU is considered equal to 1. TV programs are transmitted with horizontal polarization.

It should be remembered that CG and KNI are not necessarily interrelated. There are antennas (for example, “spy” - single-wire traveling wave antenna, ABC) with high directivity, but single or lower gain. These look into the distance as if through a diopter sight. On the other hand, there are antennas, e.g. Z-antenna, which combines low directivity with significant gain.

About the intricacies of manufacturing

All antenna elements through which useful signal currents flow (specifically, in the descriptions of individual antennas) must be connected to each other by soldering or welding. In any prefabricated unit in the open air, the electrical contact will soon be broken, and the parameters of the antenna will deteriorate sharply, up to its complete unusability.

This is especially true for points of zero potential. In them, as experts say, there is a voltage node and a current antinode, i.e. its greatest value. Current at zero voltage? Nothing surprising. Electrodynamics has moved as far from Ohm's law on direct current as the T-50 has gone from a kite.

Places with zero potential points for digital antennas are best made bent from solid metal. A small “creeping” current in welding when receiving the analogue in the picture will most likely not affect it. But, if a digital signal is received at the noise level, then the tuner may not see the signal due to the “creep”. Which, with pure current at the antinode, would give stable reception.

About cable soldering

The braid (and often the central core) of modern coaxial cables is made not of copper, but of corrosion-resistant and inexpensive alloys. They solder poorly and if you heat them for a long time, you can burn out the cable. Therefore, you need to solder the cables with a 40-W soldering iron, low-melting solder and with flux paste instead of rosin or alcohol rosin. There is no need to spare the paste; the solder immediately spreads along the veins of the braid only under a layer of boiling flux.

Types of antennas

All-wave

An all-wave (more precisely, frequency-independent, FNA) antenna is shown in Fig. It consists of two triangular metal plates, two wooden slats, and a lot of enameled copper wires. The diameter of the wire does not matter, and the distance between the ends of the wires on the slats is 20-30 mm. The gap between the plates to which the other ends of the wires are soldered is 10 mm.

Note: Instead of two metal plates, it is better to take a square of one-sided foil fiberglass with triangles cut out of copper.

The width of the antenna is equal to its height, the opening angle of the blades is 90 degrees. The cable routing diagram is shown there in Fig. The point marked in yellow is the point of quasi-zero potential. There is no need to solder the cable braid to the fabric in it; just tie it tightly, and the capacity between the braid and the fabric will be enough for matching.

The CHNA, stretched in a window 1.5 m wide, receives all meter and DCM channels from almost all directions, except for a dip of about 15 degrees in the plane of the canvas. This is its advantage in places where it is possible to receive signals from different television centers; it does not need to be rotated. Disadvantages - single gain and zero gain, therefore, in the interference zone and outside the zone of reliable reception, the CNA is not suitable.

Note : There are other types of CNA, for example. in the form of a two-turn logarithmic spiral. It is more compact than the CNA made of triangular sheets in the same frequency range, therefore it is sometimes used in technology. But in everyday life this does not provide any advantages, it is more difficult to make a spiral CNA, and it is more difficult to coordinate with a coaxial cable, so we are not considering it.

Based on the CHNA, the once very popular fan vibrator (horns, flyer, slingshot) was created, see fig. Its directivity factor and coefficient of performance are something around 1.4 with a fairly smooth frequency response and linear phase response, so it would be suitable for digital use even now. But - it works only on HF (channels 1-12), and digital broadcasting is on UHF. However, in the countryside, with an elevation of 10-12 m, it may be suitable for receiving an analogue. Mast 2 can be made of any material, but fastening strips 1 are made of a good non-wetting dielectric: fiberglass or fluoroplastic with a thickness of at least 10 mm.

Beer all-wave

The all-wave antenna made from beer cans is clearly not the fruit of the hangover hallucinations of a drunken radio amateur. This is truly a very good antenna for all reception situations, you just need to do it right. And it’s extremely simple.

Its design is based on the following phenomenon: if you increase the diameter of the arms of a conventional linear vibrator, then its operating frequency band expands, but other parameters remain unchanged. In long-distance radio communications, since the 20s, the so-called Nadenenko's dipole based on this principle. And beer cans are just the right size to serve as the arms of a vibrator on the UHF. In essence, the CHNA is a dipole, the arms of which expand indefinitely to infinity.

The simplest beer vibrator made of two cans is suitable for indoor analogue reception in the city, even without coordination with the cable, if its length is no more than 2 m, on the left in Fig. And if you assemble a vertical in-phase array from beer dipoles with a step of half a wave (on the right in the figure), match it and balance it using an amplifier from a Polish antenna (we will talk about it later), then thanks to the vertical compression of the main lobe of the pattern, such an antenna will give good CU.

The gain of the “tavern” can be further increased by adding a CPD at the same time, if a mesh screen is placed behind it at a distance equal to half the grid pitch. The beer grill is mounted on a dielectric mast; The mechanical connections between the screen and the mast are also dielectric. The rest is clear from the following. rice.

Note: the optimal number of lattice floors is 3-4. With 2, the gain in gain will be small, and more is difficult to coordinate with the cable.

Video: making a simple antenna from beer cans

"Speech therapist"

A log-periodic antenna (LPA) is a collecting line to which halves of linear dipoles (i.e., pieces of conductor a quarter of the operating wavelength) are alternately connected, the length and distance between which vary in geometric progression with an index less than 1, in the center in Fig. The line can be either configured (with a short circuit at the end opposite to the cable connection) or free. An LPA on a free (unconfigured) line is preferable for digital reception: it comes out longer, but its frequency response and phase response are smooth, and the matching with the cable does not depend on frequency, so we will focus on it.

The LPA can be manufactured for any predetermined frequency range, up to 1-2 GHz. When the operating frequency changes, its active region of 1-5 dipoles moves back and forth along the canvas. Therefore, the closer the progression indicator is to 1, and accordingly the smaller the antenna opening angle, the greater the gain it will give, but at the same time its length increases. At UHF, 26 dB can be achieved from an outdoor LPA, and 12 dB from a room LPA.

LPA can be said to be an ideal digital antenna based on its totality of qualities, so let’s look at its calculation in a little more detail. The main thing you need to know is that an increase in the progression indicator (tau in the figure) gives an increase in gain, and a decrease in the LPA opening angle (alpha) increases the directivity. A screen is not needed for the LPA; it has almost no effect on its parameters.

Calculation of digital LPA has the following features:

1. They start it, for the sake of frequency reserve, with the second longest vibrator.
2. Then, taking the reciprocal of the progression index, the longest dipole is calculated.
3. After the shortest dipole based on the given frequency range, another one is added.

Let's explain with an example. Let's say our digital programs are in the range of 21-31 TVK, i.e. at 470-558 MHz in frequency; wavelengths, respectively, are 638-537 mm. Let’s also assume that we need to receive a weak noisy signal far from the station, so we take the maximum (0.9) progression rate and the minimum (30 degrees) opening angle. For the calculation, you will need half the opening angle, i.e. 15 degrees in our case. The opening can be further reduced, but the length of the antenna will increase exorbitantly, in cotangent terms.

We consider B2 in Fig: 638/2 = 319 mm, and the arms of the dipole will be 160 mm each, you can round up to 1 mm. The calculation will need to be carried out until you get Bn = 537/2 = 269 mm, and then calculate another dipole.

Now we consider A2 as B2/tg15 = 319/0.26795 = 1190 mm. Then, through the progression indicator, A1 and B1: A1 = A2/0.9 = 1322 mm; B1 = 319/0.9 = 354.5 = 355 mm. Next, sequentially, starting with B2 and A2, we multiply by the indicator until we reach 269 mm:

• B3 = B2*0.9 = 287 mm; A3 = A2*0.9 = 1071 mm.
• B4 = 258 mm; A4 = 964 mm.

Stop, we are already less than 269 mm. We check whether we can meet the gain requirements, although it is clear that we can’t: to get 12 dB or more, the distances between the dipoles should not exceed 0.1-0.12 wavelengths. In this case, for B1 we have A1-A2 = 1322 – 1190 = 132 mm, which is 132/638 = 0.21 wavelengths of B1. We need to “pull up” the indicator to 1, to 0.93-0.97, so we try different ones until the first difference A1-A2 is reduced by half or more. For a maximum of 26 dB, you need a distance between dipoles of 0.03-0.05 wavelengths, but not less than 2 dipole diameters, 3-10 mm at UHF.

Note: cut off the rest of the line behind the shortest dipole; it is needed only for calculations. Therefore, the actual length of the finished antenna will be only about 400 mm. If our LPA is external, this is very good: we can reduce the opening, obtaining greater directionality and protection from interference.

Video: antenna for digital TV DVB T2

About the line and the mast

The diameter of the tubes of the LPA line on the UHF is 8-15 mm; the distance between their axes is 3-4 diameters. Let’s also take into account that thin “lace” cables give such attenuation per meter on the UHF that all antenna-amplification tricks will come to naught. You need to take a good coaxial for an outdoor antenna, with a shell diameter of 6-8 mm. That is, the tubes for the line must be thin-walled, seamless. You cannot tie the cable to the line from the outside; the quality of the LPA will drop sharply.

It is necessary, of course, to attach the outer propulsion boat to the mast by the center of gravity, otherwise the small windage of the propulsion craft will turn into a huge and shaking one. But it is also impossible to connect a metal mast directly to the line: you need to provide a dielectric insert of at least 1.5 m in length. The quality of the dielectric does not play a big role here; oiled and painted wood will do.

About the Delta antenna

If the UHF LPA is consistent with the cable amplifier (see below, about Polish antennas), then the arms of a meter dipole, linear or fan-shaped, like a “slingshot”, can be attached to the line. Then we will get a universal VHF-UHF antenna of excellent quality. This solution is used in the popular Delta antenna, see fig.

Antenna “Delta”

Zigzag on air

A Z-antenna with a reflector gives the same gain and gain as the LPA, but its main lobe is more than twice as wide horizontally. This can be important in rural areas when there is TV reception from different directions. And the decimeter Z-antenna has small dimensions, which is essential for indoor reception. But its operating range is theoretically not unlimited; frequency overlap while maintaining parameters acceptable for the digital range is up to 2.7.

The design of the MV Z-antenna is shown in Fig; The cable route is highlighted in red. There in the lower left there is a more compact ring version, colloquially known as a “spider”. It clearly shows that the Z-antenna was born as a combination of a CNA with a range vibrator; There is also something of a rhombic antenna in it, which does not fit into the theme. Yes, the “spider” ring does not have to be wooden, it can be a metal hoop. "Spider" receives 1-12 MV channels; The pattern without a reflector is almost circular.

The classic zigzag works either on 1-5 or 6-12 channels, but for its manufacture you only need wooden slats, enameled copper wire with d = 0.6-1.2 mm and several scraps of foil fiberglass, so we give the dimensions in fraction for 1-5/6-12 channels: A = 3400/950 mm, B, C = 1700/450 mm, b = 100/28 mm, B = 300/100 mm. At point E there is zero potential; here you need to solder the braid to a metallized support plate. Reflector dimensions, also 1-5/6-12: A = 620/175 mm, B = 300/130 mm, D = 3200/900 mm.

The range Z-antenna with a reflector gives a gain of 12 dB, tuned to one channel - 26 dB. To build a single-channel one based on a band zigzag, you need to take the side of the square of the canvas in the middle of its width at a quarter of the wavelength and recalculate all other dimensions proportionally.

Folk Zigzag

As you can see, the MV Z-antenna is a rather complex structure. But its principle shows itself in all its glory on the UHF. The UHF Z-antenna with capacitive inserts, combining the advantages of the “classics” and the “spider”, is so easy to make that even in the USSR it earned the title of folk antenna, see fig.

Material – copper tube or aluminum sheet with a thickness of 6 mm. The side squares are solid metal or covered with mesh, or covered with a tin. In the last two cases, they need to be soldered along the circuit. The coax cannot be bent sharply, so we guide it so that it reaches the side corner, and then does not go beyond the capacitive insert (side square). At point A (zero potential point), we electrically connect the cable braid to the fabric.

Note: aluminum cannot be soldered with conventional solders and fluxes, so “folk” aluminum is suitable for outdoor installation only after sealing the electrical connections with silicone, since everything in it is screwed.

Video: example of a double triangle antenna

Wave channel

The wave channel antenna (AWC), or Udo-Yagi antenna, available for self-production, is capable of giving the highest gain, directivity factor and efficiency factor. But it can only receive digital signals on UHF on 1 or 2-3 adjacent channels, because belongs to the class of highly tuned antennas. Its parameters deteriorate sharply beyond the tuning frequency. It is recommended to use AVK under very poor reception conditions, and make a separate one for each TVK. Fortunately, this is not very difficult - AVK is simple and cheap.

The operation of the AVK is based on “raking” the electromagnetic field (EMF) of the signal to the active vibrator. Externally small, lightweight, with minimal windage, the AVK can have an effective aperture of dozens of wavelengths of the operating frequency. Directors (directors) that are shortened and therefore have capacitive impedance (impedance) direct the EMF to the active vibrator, and the reflector (reflector), elongated, with inductive impedance, throws back to it what has slipped past. Only 1 reflector is needed in an AVK, but there can be from 1 to 20 or more directors. The more there are, the higher the gain of the AVC, but the narrower its frequency band.

From interaction with the reflector and directors, the wave impedance of the active (from which the signal is taken) vibrator drops the more, the closer the antenna is tuned to the maximum gain, and coordination with the cable is lost. Therefore, the active dipole AVK is made into a loop, its initial wave impedance is not 73 Ohms, like a linear one, but 300 Ohms. At the cost of reducing it to 75 Ohms, an AVK with three directors (five-element, see the figure on the right) can be adjusted to almost a maximum gain of 26 dB. A characteristic pattern for AVK in the horizontal plane is shown in Fig. at the beginning of the article.

AVK elements are connected to the boom at points of zero potential, so the mast and boom can be anything. Propylene pipes work very well.

Calculation and adjustment of AVK for analog and digital are somewhat different. For analogue, the wave channel must be calculated at the carrier frequency of the image Fi, and for digital – at the middle of the TVC spectrum Fc. Why this is so - unfortunately, there is no room to explain here. For the 21st TVC Fi = 471.25 MHz; Fс = 474 MHz. UHF TVCs are located close to each other at 8 MHz, so their tuning frequencies for AVK are calculated simply: Fn = Fi/Fс(21 TVC) + 8(N – 21), where N is the number of the desired channel. Eg. for 39 TVCs Fi = 615.25 MHz, and Fc = 610 MHz.

In order not to write down a lot of numbers, it is convenient to express the dimensions of the AVK in fractions of the operating wavelength (it is calculated as A = 300/F, MHz). The wavelength is usually denoted by the small Greek letter lambda, but since there is no default Greek alphabet on the Internet, we will conventionally denote it by the large Russian L.

The dimensions of the digitally optimized AVK, according to the figure, are as follows:

• P = 0.52L.
• B = 0.49L.
• D1 = 0.46L.
• D2 = 0.44L.
• D3 = 0.43l.
• a = 0.18L.
• b = 0.12L.
• c = d = 0.1L.

If you don’t need a lot of gain, but reducing the size of the AVK is more important, then D2 and D3 can be removed. All vibrators are made of a tube or rod with a diameter of 30-40 mm for 1-5 TVKs, 16-20 mm for 6-12 TVKs and 10-12 mm for UHF.

AVK requires precise coordination with the cable. It is the careless implementation of the matching and balancing device (CMD) that explains most of the failures of amateurs. The simplest USS for AVK is a U-loop made from the same coaxial cable. Its design is clear from Fig. on right. The distance between signal terminals 1-1 is 140 mm for 1-5 TVKs, 90 mm for 6-12 TVKs and 60 mm for UHF.

Theoretically, the length of the knee l should be half the length of the working wave, and this is what is indicated in most publications on the Internet. But the EMF in the U-loop is concentrated inside the cable filled with insulation, so it is necessary (for numbers - especially mandatory) to take into account its shortening factor. For 75-ohm coaxials it ranges from 1.41-1.51, i.e. l you need to take from 0.355 to 0.330 wavelengths, and take exactly so that the AVK is an AVK, and not a set of pieces of iron. The exact value of the shortening factor is always in the cable certificate.

Recently, the domestic industry has begun to produce reconfigurable AVK for digital, see Fig. The idea, I must say, is excellent: by moving the elements along the boom, you can fine-tune the antenna to local reception conditions. It is better, of course, for a specialist to do this - the element-by-element adjustment of the AVC is interdependent, and an amateur will certainly get confused.

About “Poles” and amplifiers

Many users have Polish antennas, which previously received analogue decently, but refuse to accept digital - they break or even disappear completely. The reason, I beg your pardon, is the obscene commercial approach to electrodynamics. Sometimes I feel ashamed for my colleagues who have concocted such a “miracle”: the frequency response and phase response resemble either a psoriasis hedgehog or a horse’s comb with broken teeth.

The only good thing about the Poles is their antenna amplifiers. Actually, they do not allow these products to die ingloriously. Belt amplifiers are, firstly, low-noise, broadband. And, more importantly, with a high-impedance input. This allows, at the same strength of the EMF signal on the air, to supply several times more power to the tuner input, which makes it possible for the electronics to “rip out” a number from very ugly noise. In addition, due to the high input impedance, the Polish amplifier is an ideal USS for any antennas: whatever you attach to the input, the output is exactly 75 Ohms without reflection or creep.

However, with a very poor signal, outside the zone of reliable reception, the Polish amplifier no longer works. Power is supplied to it via a cable, and power decoupling takes away 2-3 dB of the signal-to-noise ratio, which may not be enough for the digital signal to go right into the outback. Here you need a good TV signal amplifier with separate power supply. It will most likely be located near the tuner, and the control system for the antenna, if required, will have to be made separately.

The circuit of such an amplifier, which has shown almost 100% repeatability even when implemented by novice radio amateurs, is shown in Fig. Gain adjustment – ​​potentiometer P1. The decoupling chokes L3 and L4 are standard purchased ones. Coils L1 and L2 are made according to the dimensions in the wiring diagram on the right. They are part of signal bandpass filters, so small deviations in their inductance are not critical.

However, the installation topology (configuration) must be observed exactly! And in the same way, a metal shield is required, separating the output circuits from the other circuit.

Where to begin?

We hope that experienced craftsmen will find some useful information in this article. And for beginners who don’t yet feel the air, it’s best to start with a beer antenna. The author of the article, by no means an amateur in this field, was quite surprised at one time: the simplest “pub” with ferrite matching, as it turned out, takes the MV no worse than the proven “slingshot”. And what it costs to do both - see the text.

(2 ratings, average: 4,00 out of 5)

Said):

And on the roof there was a satisfactory reception for Polyachka. I’m 70–80 kilometers from the television center. These are the problems I have. From the balcony you can catch 3-4 pieces from 30 channels, and then with “cubes”. Sometimes I watch TV channels from the Internet on the computer in my room, but my wife cannot watch her favorite channels normally on her TV. Neighbors advise installing cable, but you have to pay for it every month, and I already pay for the Internet, and my pension is not flexible. We keep pulling and pulling and there’s not enough for everything.

Pyotr Kopitonenko said:

It’s not possible to install an antenna on the roof of the house; the neighbors swear that I walk around and break the roofing material covering and then their ceiling leaks. Actually, I am very “grateful” to that economist who received a prize for saving money. He came up with the idea of ​​removing the expensive gable roof from the houses and replacing it with a flat roof covered with poor roofing material. The economist received money for saving, and the people on the top floors now suffer all their lives. Water flows on their heads and on their beds. They change the roofing felt every year, but it becomes unusable within a season. In frosty weather, it cracks and rainwater and snow flow into the apartment, even if no one walks on the roof!!!

Sergey said:

Greetings!
Thanks for the article, who is the author (I don’t see the signature)?
The LPA works perfectly according to the above method, UHF channels 30 and 58. Tested in the city (reflected signal) and outside the city, distances to the transmitter (1 kW) respectively: 2 and 12 km approximately. Practice has shown that there is no urgent need for the “B1” dipole, but another dipole before the shortest one has a significant effect, judging by the signal intensity in %. Especially in city conditions, where you need to catch (in my case) the reflected signal. Only I made an antenna with a “short circuit”, it turned out that way, there was simply no suitable insulator.
In general, I recommend it.

Vasily said:

IMHO: people looking for an antenna to receive digital TV, forget about the LPA. These wide-range antennas were created in the second half of the 50s (!!) of the last century in order to catch foreign television centers while on the shores of the Soviet Baltic states. In magazines of the time, this was bashfully called “extra-long-range reception.” Well, we really loved watching Swedish porn at night on the Riga seaside...

In terms of purpose, I can say the same about “double, triple, etc. squares”, as well as any “zigzags”.

Compared to a “wave channel” of similar range and gain, LPAs are more bulky and material-intensive. Calculating the LPA is complex, intricate and more like fortune telling and adjusting the results.

If in your region ECTV is broadcast on neighboring UHF channels (I have 37-38), then the best solution is to find a book online: Kapchinsky L.M. Television antennas (2nd edition, 1979) and make a “wave channel” for a group of UHF channels (if you broadcast above 21-41 channels, you will have to recalculate) described on page 67 et seq. (Fig. 39, Table 11).
If the transmitter is 15 - 30 km away, the antenna can be simplified by making it four - five element, simply without installing directors D, E and Zh.

For very close transmitters, I recommend indoor antennas; by the way, in the same book on pp. 106 – 109 there are drawings of wide-range indoor “wave channel” and LPA. The “wave channel” is visually smaller, simpler and sleeker with higher gain!

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Previously, it was difficult to purchase a ready-made, high-quality television antenna. Craftsmen, using radio engineering knowledge, independently constructed decent samples that reliably received the on-air signal. Times have changed, digital television has replaced analogue, but the problem of having a good decimeter antenna in places with difficult conditions remains relevant.

The evolution of television broadcasting

A number of changes have occurred in broadcast television that must be taken into account before making a decimeter antenna with your own hands:

1. Now almost all TV broadcasting is produced in the UHF range. One of the reasons is the economic factor. Equipment of transmitting stations: antennas, feeders are significantly reduced in price. The need for their preventive maintenance by highly qualified specialists is reduced;
2. The TV signal covers all places that were previously inaccessible. In “blind corners” coverage is provided by a transmitter without maintenance personnel;
3. Digital television signal has its own characteristic features. It feels little interference, but if the cable is mismatched, or there are phase distortions in any place in the receiving-transmitting path, the image may be “torn” even with a high signal quality;
4. Television has a huge number of programs, and it makes no sense to configure the UHF antenna for several channels;
5. Urban conditions for the transmission of waves have been transformed due to the rapid construction of multi-story buildings, the reinforced concrete buildings of which are capable of repeatedly reflecting them before gradually fading.

The length of the LW wave is in the range of 0.1-1 m. Hence its name. Electromagnetic waves can only propagate in the forward direction, without going around obstacles. Therefore, for long distances such communication is problematic. Its coverage radius is 100 km. The UHF antenna must be manufactured taking into account the changing requirements.

Modern requirements

1. Previously, the decisive importance was given to the coefficients of directional and protective action. This is not the case now. The airwaves have become heavily polluted, and it is necessary to overcome the interference by electronic means;
2. The individual antenna gain comes first. Such a UHF antenna can create the necessary margin of safety for the signal, which will subsequently be processed by electronics;
3. It is important to ensure the smoothness of the amplitude-frequency response. Sharp peaks and valleys will cause phase distortion;
4. Coordination with the cable over the entire frequency range must be complete without the use of additional devices;
5. The antenna parameters must meet the requirements over the entire frequency range initially. The band antenna does not need to be artificially adapted using engineering tricks.

Properties of different types of antennas

Antennas suitable for self-production:

1. All-wave. Does not depend on frequency. UHF antenna with the lowest parameters. But it is the easiest and cheapest to do. It is good to use for a TV in a country house, where, under relatively clear air conditions, the device can receive a digital signal. Copes well with receiving an analog signal near a television center;
2. Log-periodic range. This is also an easy option. Accurately matches the outgoing feeder within its range. It filters out certain frequencies. Has average characteristics. Serves well as an indoor antenna in a city house or apartment;
3. Zigzag or Z-type. If this is an MV antenna, then it is much more difficult to make it. It is required to make complex calculations and spend a lot of time on manufacturing. In the decimeter range, all dimensions are reduced, calculations are simplified, and an effective antenna is obtained for indoor or outdoor use with virtually any signal quality.

Important! Perfect matching and symmetry of the antenna can be achieved by laying the cable across the “zero” (the point with zero potential, where the currents are maximum and the voltage is zero).

Antenna parameters

A decimeter antenna can be made with your own hands with a minimum of theoretical knowledge, but it is necessary to practically understand the meaning of its parameters.

1. Gain factor (GC) is the relative increase in radiation at the moment of the peak, the value of which (dB) is higher than the reference (dipole of 0.5 wavelength);
2. Directional coefficient (DC) - in numerical terms, the ratio of the incoming power arriving at the TV from a directional antenna to the same power from an omnidirectional dipole of 0.5 wavelengths;
3. The protective action coefficient (PFC) is the ratio of the power that the antenna releases when receiving a side or rear signal to the power from the main direction.

The radiation pattern for the antennas is reproduced in the form of lobes. The directivity of the antenna is determined by the width of the main lobe, and the immunity from interference is determined by the level of the side and rear lobes.

A similar homemade outdoor antenna, known as a "horn" (fan vibrator), was often used to receive broadcast signals not so long ago. In terms of parameters, it would be suitable for “digital”. But it is used only for receiving MV from channels 1 to 12. Using the same principle, you can make a UHF antenna.

The simplest design consists of metal plates in the form of isosceles triangles. The triangles need to be positioned so that their right angles are towards each other with a gap of about 1 cm. Along the hypotenuses, you need to strengthen two slats and install copper wires (enameled) of any diameter at a distance of 2-2.5 cm from each other. The width and height of the decimeter antenna are the same. When attaching the cable at a point with zero potential, it can be tied without soldering.

If you stretch such an antenna in the area of ​​a window, one and a half meters wide, then it will receive a TV signal from any direction, without additional rotation. The disadvantage of the design is the low gain, and the efficiency factor is completely zero. So in places with strong interference and a very weak signal, using an antenna is problematic.

Important. Sometimes radio amateurs try to make an omnidirectional antenna using a helix instead of a triangle, since it is smaller in size for similar frequencies. But it is more difficult to construct this type of UHF antenna with your own hands. Coordination with the cable also causes difficulties.

A type of all-wave antenna, easy to manufacture, allowing you to get a decent image. Well suited for use in environments with a strong but intermittent signal. The device is a classical dipole circuit. Due to their size, 0.5-liter aluminum cans are ideal for use as arms of a UHF vibrator. If you take jars of larger or smaller dimensions, the reception frequencies will change. The basis is the principle that when the diameter of the vibrator arms (linear) increases, the operating frequency range expands while maintaining other characteristics.

The simplest antenna of two cans is suitable as an indoor antenna for receiving an analog signal. The cable is not even subject to approval if its length is no more than two meters.

Sequencing:

1. Attach a plug to one end of the cable to connect to the TV, strip the other by removing the insulating layer, 10 centimeters from the beginning. Untwist the cable cores, remove the foil;
2. Attach the central core of the cable to one can, and the wires of the shielding braid to the other;
3. Using adhesive tape or tape, install the cans on the insulating frame with the open part facing each other. This can be a wooden plank or a regular clothes hanger.

The distance between the banks is set to approximately 7-8 cm.

Important! It is necessary to ensure a tight fit of the wires to the metal of the can.

You can assemble a whole grid from cans, increasing the protection against interference with the help of a mesh screen installed at the back. This design is used outdoors and is mounted on a dielectric mast. The screen must also be connected to the mast using dielectric materials. If you make more than 4 crossbars, then difficulties will arise in matching the cable; 2 will not provide sufficient reinforcement. The distance between the crossbars is equal to half the average wavelength of the channels to which reception needs to be tuned. If you have an amplifier, it can be mounted additionally.

Another simple antenna is made from coaxial cable. The goal is to obtain a circle-shaped frame capable of receiving a narrow range signal. An antenna for digital TV must have high immunity to interference. This design is also a selective filter that reduces interference. It works well inside apartments with reinforced concrete walls.

The disadvantage of this antenna is that the input impedance of the frame will be about 300 Ohms, and for the feeder the wave impedance will be 75 Ohms. It is necessary to install a matching device or make a frame with an input impedance of 75 Ohms. It has the shape of a rectangle (side length ratio 1:2). Both options are not very convenient. There is a third original solution - for the matching device, take the same cable and make a special loop out of it.

Based on the calculations, in the decimeter range for the ring you need to take a piece of coaxial cable 5.3 m, for a loop - 1.75 m

Making a loop antenna:

1. Cut a piece of cable for the ring and for the loop;
2. A part of the cable is bent into a ring and installed on plywood, plexiglass or other insulating material;
3. A loop is made from another piece, the ends of which should be flush with the end of the cable going to the TV or receiver. Can be fixed with tape;
4. The wires of the three shielding braids are connected to each other by soldering. The shield cores from the loop must be connected on both sides to the shielding cores of the ring. The central wire of the cable to the TV is with one side.

Note! The structure, placed outdoors, is protected from bad weather by a plastic casing.

Wave channel

The maximum gain, efficiency and interference protection for a self-made device is provided by a wave channel antenna. Suitable for use at a considerable distance from the broadcast center. In the city it is able to reduce interference, as it has precise directionality. The same property limits the number of received channels, since beyond the boundaries of the frequency selected for tuning, the antenna characteristics sharply decrease.

The antenna drawings represent a device that consists of shortened directors, or guides with capacitive reactance, an active vibrator and a reflector. The electromagnetic signal is oriented by the directors in the direction of the active vibrator. A longer reflector with inductive resistance located behind it reflects the waves passing by it.

Important! One reflector is enough, but there can be a different number of directors: up to 10 or more. With a larger number of directors, the gain increases, but the range of received frequencies decreases.

The television cable is connected to an active vibrator. Its relationship with the directors and reflector reduces its own wave resistance. The force of the fall depends on the gain. As a result, there is a mismatch with the television cable. For this reason, the active vibrator is made in the form of a loop, having an initial resistance of 300 Ohms. After interacting with several directors and a reflector, the resistance becomes 75 ohms. This ratio is valid for a five-element device.

For UHF, vibrators must be made of a metal tube from 6 to 10 mm in diameter. The total number of elements of the decimeter device is 16. All elements are connected to the boom actually at points with zero potential. This means that the material of the boom, like the mast, can be taken of any kind. For example, polypropylene pipes.

Important! The antenna must be strictly coordinated with the cable. A loop of coaxial cable can be used as a matching device.

In theory, the length of the loop is half the wavelength (the working wave is taken). But it is necessary to take into account the correction for cable insulation. When using 75 ohm coaxial cable, the loop size will be 0.35 of the wavelength. Inter-terminal distance – 6 cm.

Zigzag

Zigzag is a Kharchenko antenna circuit, refers to broadband devices. The design dimensions for the decimeter range are compact and easily allow it to be used indoors. It is especially effective in remote settlements when receiving in different directions. The limits of received frequencies while maintaining parameters overlap with a factor of 2.6-2.7.

The classic zigzag is difficult to manufacture and requires precise calculations. Widely used for receiving analogue television programs. For a digital signal, everything is greatly simplified.

Rhombus

The diamond design is a type of zigzag. The best material for the main circuit is copper tubes, another possible material is aluminum sheets (thickness 6 mm and above), cut into strips. To create a container, inserts made of tin, metal mesh or foil are used within the boundaries of small side rhombuses. A reflector is mounted at the back. Insert containers and a reflector complement the structure to increase sensitivity. If the signal is good, you can do without these elements.

Important! Mesh or tin inserts are soldered along the contour. This is not necessary when using thin metal sheets.

The coaxial cable should not be bent too much. It is brought to the side top of the diamond, and then directed to the center and soldered.

At the point with zero potential (the lower vertex of the diamond), an electrical connection must be made to the wires of the shielding braid.

Log-periodic

If the antenna does not always cope with an analog signal without adjustment, then it is ideal for receiving a digital television signal. It consists of a long rod to which halves of dipoles of different lengths are attached. The gaps between the vibrators and their length vary exponentially. Calculating an antenna is quite difficult. There are several methods presented on the Internet.

Features of a log periodic antenna:

1. The central rod feeds the right and left vibrators separately. They must be in antiphase;
2. The rod consists of two load-bearing members. Left-right vibrators take turns changing carriers. The first left is the upper carrier, the first right is the lower. The next row is the opposite;
3. The number of vibrators is determined by the design of the antenna. The longest ones, located at the back, are equal in length to the length of a half-wave of the lower limit of the range;
4. The coaxial cable is laid to the middle of the structure, passing inside one of the guides. At the exit from the nose, the central core must be connected to the second carrier. Such a line, consisting of two wires, will act as a balun transformer. There is another gasket option;
5. For better matching, the line is short-circuited behind the longest vibrator (a distance of 1/8 of the wavelength of the lower limit of the range);
6. The diameter of the tubes should be 10-15 mm for a decimeter wave.
7. Thin cables will cause high attenuation, requiring a wire of at least 6mm in diameter. The cable is tied only from the inside, otherwise the quality of the antenna decreases.

1. All structural elements with signal current flowing must be soldered or welded. This is especially true for outdoor antennas;
2. Coaxial cables do not lend themselves well to conventional soldering, and prolonged heating can damage the cable. It is best to solder using low-melting solder, replacing rosin with flux paste.

There are the simplest options for making homemade antennas and more complex ones. Depending on knowledge and accumulated experience, each user can choose an option that is personally acceptable to him.

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