Drawing of an indoor UHF airplane antenna. Subtleties of making television antennas. Antenna - half-wave linear vibrator

Digital terrestrial television (DVB-Digital Video Broadcasting) is a technology for transmitting television images and sound using digital encoding of video and sound. Digital encoding, unlike analogue, ensures signal delivery with minimal losses, since the signal is not affected by external interference. At the time of writing, 20 digital channels are available, and this number should increase in the future. This number of digital channels is not available in all regions; you can find out more precisely about the possibility of receiving digital channels on the website www.rtrs.rf. If your region has digital channels, then you just need to make sure that your TV supports DVB-T2 technology (this can be found in the documentation for the TV) or purchase a DVB-T2 set-top box and connect the antenna. The question arises - Which antenna should I use for digital television? or How to make an antenna for digital television? In this article I would like to dwell in more detail on antennas for watching digital television, and in particular I will show how to make your own antenna for digital television.

The first thing I would like to emphasize is that digital television does not require a specialized antenna; an analog antenna (the one you used previously to watch analog channels) is quite suitable. Moreover, only a television cable can be used as an antenna...

In my opinion, the simplest antenna for digital television is a television cable. Everything is extremely simple, take a coaxial cable, put an F connector and an adapter for connecting to a TV on one end, and at the other end the central core of the cable is exposed (a kind of whip antenna). All that remains is to decide how many centimeters to expose the central core, since the quality of reception of digital channels depends on this. To do this, you need to understand at what frequency digital channels broadcast in your region, to do this, go to the website www.rtrs.rf/when/ here on the map, find the tower closest to you and see at what frequency digital channels broadcast.

You will receive more detailed information if you click the "More details" button.

Now we need to calculate the wavelength. The formula is very simple:

where, λ (lamda) is the wavelength,

c - speed of light (3-10 8 m/s)

F - frequency in hertz

or simpler λ=300/F (MHz)

In my case, the frequency is 602 MHz and 610 MHz, for the calculation I will use the frequency of 602 MHz

Total: 300/ 602 ≈ 0.5 m = 50 cm.

Leaving half a meter of the central core of a coaxial cable is not beautiful and inconvenient, so I will leave half, or maybe a quarter, of the wavelength.

l=λ*k/2

where l is the length of the antenna (central core)

λ - wavelength (calculated earlier)

k - shortening factor, since the length of the entire cable will not be large, this value can be considered equal to 1.

As a result, l=50/2=25 cm.

From these calculations it turned out that for a frequency of 602 MHz I need to expose 25 cm of coaxial cable.

Here is the result of the work done

This is what the antenna looks like when installed.

View of the antenna when watching TV.

Content:

In country houses and summer cottages, problems often arise with the reception of television signals due to the lack of amplification. This may be due to terrain features, the presence of trees and other factors. Therefore, many owners of private property are wondering how to make an antenna for digital TV with their own hands. If you have certain knowledge and skills in working with a soldering iron, this problem can be solved quite easily. Such antennas are distinguished by their simple design, good reception quality, reliability and low cost.

Simple TV antenna

The repeater, located up to 30 km from the place where the signal is received, allows you to use the simple design of a television antenna. It consists of two tubes connected to each other by a shielded cable. The output part of the cable is supplied to the corresponding input of the TV.

Before constructing such an antenna, you need to find out the broadcast frequency of the nearest TV tower. Typically, the broadcast band range is from 50 to 230 MHz. The entire band is divided into 12 channels, each of which corresponds to a certain length of tubes. They are selected using a special table. As the channel frequency increases, the length of the tubes and cables will decrease.

Materials for making the antenna:

Metal tube with a diameter of 8-24 mm, made of steel, brass, duralumin and other metals. The most commonly used diameter is 16 mm. Both tubes must have exactly the same parameters, down to the wall thickness.
The required amount of television cable with a resistance of 75 Ohms.
Getinaks or textolite for the holder, at least 4 mm thick.
Clamps or metal strips used to secure pipes.
The antenna stand can be made from a metal pipe or corner. If the height is low, you can use wooden blocks.
You will definitely need a soldering iron, solder and copper. Silicone, epoxy resin or electrical tape are used to protect solder joints.

How to assemble the antenna:

First, the tube is cut to the required length corresponding to the broadcast frequency and sawed exactly in half.
Each tube should be flattened on one side and attached to the holder with these ends. The distance between the near tubes is 6-7 cm, between the far ones - in accordance with the table. Fastening is carried out using clamps.
The resulting structure is fixed to a rack or mast. Then, the near ends are connected to each other with a cable loop. The middle cores of the cable are soldered to the flattened ends, and their braiding is connected with the same conductor.
A connection is made between the central conductors of the loop and the cable supplied to the TV. Their shield is also connected using copper wire.

After completing all the steps, the loop is attached to the rod in the center, and the cable going down is also screwed here. It is better to set up the antenna together: one person is needed to rotate the antenna, and the other is needed to view and evaluate the image quality. After establishing the highest quality signal reception, the antenna is fixed in this position. You can navigate by the direction of the receivers installed in neighboring houses.

Pipe loop antenna

The manufacturing process of a loop antenna is considered more complex compared to the previous version. This is due to the use of a pipe bender. However, the basic materials remain the same. You will need a metal tube, cable and material for the stand. This design allows you to receive a signal at a distance of up to 40 kilometers.

The pipe can be bent to any radius. It is of great importance to comply with the required length and distance between the ends, which ranges from 65 to 70 mm. Each half of the curved pipe must be the same length. The center of the mast is the axis of symmetry for both ends. The selection of pipe and cable lengths is also carried out using a special table. The average diameter of the tube is 12-18 millimeters.

Antenna assembly procedure:

The tube is sawed off to the required length, after which it is bent at both ends so that they are symmetrical relative to the center.
One edge of the tube is flattened and then capped by welding or soldering. After this, its internal cavity is filled with sand, and the second side of the pipe is also sealed. If there is no welding, you can use plugs with glue or silicone.
The resulting antenna structure is mounted on a stand. The central wires of the cable loop are fixed to the ends of the pipe. A cable leading to the TV is screwed to one end. The cable braid is connected by copper wire with the insulation removed. All joints are carefully soldered.

After assembling and installing the antenna, it is configured in the same way as for the previous design.

Beer cans for outdoor antenna

Antennas made from beer cans are characterized by high signal reception quality. To make this design you will need 2 0.5 liter beer cans, a piece of wood or plastic approximately 0.5 m long, a television cable, a soldering iron, solder and flux.

Digital antenna assembly:

In the center of the bottom of each jar you need to drill a hole with a diameter of 5-6 mm. The cable is pulled through it and exited through the hole in the cover.
The finished jar is secured to the left on a wooden or plastic holder. The direction of the cable should be towards the center of the holder.
Then, a part of the cable, 5-6 cm long, is pulled out from this can. You need to remove about 3 cm of insulation from it and disassemble the braid.
The freed braid is cut to a length of 1.5 cm, distributed along the plane of the can and soldered.
The central conductor, protruding 3 cm, is soldered to the bottom of another can.
The distance between the cans should be minimal and fixed with electrical tape or tape.

This completes the antenna assembly. Next, the entire structure is installed and configured. The required plug is installed on the free end of the cable and plugged into the corresponding socket on the TV. All contact points must be carefully soldered and protected from external influences.

Frame antenna design

To make a loop antenna you will need a television cable and a wooden cross as a base. Fastenings will be made using electrical tape and nails. First of all, it is necessary to calculate the perimeter of the copper wire frames. To make the frames, a wire is taken from a television cable. Calculations are carried out in accordance with the broadcast frequency and channel number.

Before starting assembly, you need to remove the insulation and braiding from the television cable and free the central wire to the required length. The frames for the antenna will be made from it. This procedure requires extreme caution to prevent damage to the copper core.

The wooden frame is made according to the dimensions of the frames. First, the main points - the corners - are marked with nails. The distance between them from one nail to another will correspond to the side of the square. Laying the conductor starts from the middle on the right, then it passes through all the designated points. The frames at the minimum distance must not touch each other to avoid short circuits. The gap between the conductors is on average 2-3 cm.

After laying the entire perimeter, 3-4 cm of braid is removed from the cable, which is twisted into a bundle and soldered to the left edge of the frame. The rest of the cable is laid along the core and secured with electrical tape. Next, it is supplied to the decoder and this is where the installation process ends. Thus, the question of how to make an antenna for digital TV with your own hands can be solved in several ways. A special feature of these devices is the ability to tune to only one frequency. Therefore, the design of such an antenna is simple and effective.

DIY digital TV antenna

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 given 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.

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:

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.
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.
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 that DIYers can do is set up a satellite dish; read about that here.

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):

To determine antenna parameters

KU is the ratio of the signal power received by the antenna on the main (main) lobe of its DP 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:

If the antenna is a band antenna, the powers are calculated at the frequency of the useful signal.
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.

Frequency independent antenna with horizontal polarization

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 into 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.

Fan vibrator for receiving MV TV

Beer all-wave

Beer can antennas

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 “pivnuha” 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.

In-phase array of beer dipoles

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.

"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.

Log-periodic antenna design

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:

They start it, for the sake of frequency reserve, with the second longest vibrator.
Then, taking the reciprocal of the progression index, the longest dipole is calculated.
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.

Delta antenna

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.

Z-antenna MV

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 range 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.

People's UHF antenna

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

Wave channel antenna

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:

U-loop: USS for AVK

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 AVCs for digital use, 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.

AVK for digital TV

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.

UHF TV signal amplifier

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.

Despite the rapid development of satellite and cable television, the reception of terrestrial television broadcasts still remains relevant, for example, for places of seasonal residence. It is not at all necessary to buy a finished product for this purpose; a home UHF antenna can be assembled with your own hands. Before moving on to considering the designs, we will briefly explain why this particular range of the television signal was chosen.

Why DMV?

There are two good reasons to choose designs of this type:

The thing is that most channels are broadcast in this range, since the design of repeaters is simplified, and this makes it possible to install a larger number of unattended low-power transmitters and thereby expand the coverage area.
This range is selected for digital broadcasting.

Indoor TV antenna “Rhombus”

This simple, but at the same time, reliable design was one of the most common in the heyday of on-air television broadcasting.

Rice. 1. The simplest homemade Z-antenna, known under the names: “Rhombus”, “Square” and “People’s Zigzag”

As can be seen from the sketch (B Fig. 1), the device is a simplified version of the classic zigzag (Z-design). To increase sensitivity, it is recommended to equip it with capacitive inserts (“1” and “2”), as well as a reflector (“A” in Fig. 1). If the signal level is quite acceptable, this is not necessary.

The material you can use is aluminum, copper, and brass tubes or strips 10-15 mm wide. If you plan to install the structure outdoors, it is better to abandon aluminum, since it is susceptible to corrosion. Capacitive inserts are made of foil, tin or metal mesh. After installation, they are soldered along the circuit.

The cable is laid as shown in the figure, namely: it did not have sharp bends and did not leave the side insert.

UHF antenna with amplifier

In places where a powerful relay tower is not located in relative proximity, you can raise the signal level to an acceptable value using an amplifier. Below is a schematic diagram of a device that can be used with almost any antenna.

Rice. 2. Antenna amplifier circuit for the UHF range

List of elements:

Resistors: R1 – 150 kOhm; R2 – 1 kOhm; R3 – 680 Ohm; R4 – 75 kOhm.
Capacitors: C1 – 3.3 pF; C2 – 15 pF; C3 – 6800 pF; C4, C5, C6 – 100 pF.
Transistors: VT1, VT2 – GT311D (can be replaced with: KT3101, KT3115 and KT3132).

Inductance: L1 – is a frameless coil with a diameter of 4 mm, wound with copper wire Ø 0.8 mm (2.5 turns must be made); L2 and L3 are high-frequency chokes 25 µH and 100 µH, respectively.

If the circuit is assembled correctly, we will get an amplifier with the following characteristics:

bandwidth from 470 to 790 MHz;
gain and noise factors – 30 and 3 dB, respectively;
the value of the output and input resistance of the device corresponds to the RG6 cable – 75 Ohm;
the device consumes about 12-14 mA.

Let's pay attention to the method of power supply; it is carried out directly through the cable.

This amplifier can work with the simplest designs made from improvised means.

Indoor antenna made from beer cans

Despite the unusual design, it is quite functional, since it is a classic dipole, especially since the dimensions of a standard can are perfectly suitable for the arms of a decimeter range vibrator. If the device is installed in a room, then in this case it is not even necessary to coordinate with the cable, provided that it is not longer than two meters.

Designations:

A - two cans with a volume of 500 mg (if you take tin and not aluminum, you can solder the cable instead of using screws).
B – places where the cable shielding is attached.
C – central vein.
D – place of attachment of the central core
E – cable coming from the TV.

The arms of this exotic dipole must be mounted on a holder made of any insulating material. As such, you can use improvised things, for example, a plastic clothes hanger, a mop bar or a piece of wooden beam of the appropriate size. The distance between the shoulders is from 1 to 8 cm (selected empirically).

The main advantages of the design are fast production (10 - 20 minutes) and quite acceptable picture quality, provided there is sufficient signal power.

Making an antenna from copper wire

There is a design that is much simpler than the previous version, which only requires a piece of copper wire. We are talking about a narrow band loop antenna. This solution has undoubted advantages, since in addition to its main purpose, the device plays the role of a selective filter that reduces interference, which allows you to confidently receive a signal.

Fig.4. A simple UHF loop antenna for receiving digital TV

For this design, you need to calculate the length of the loop; to do this, you need to find out the frequency of the “digit” for your region. For example, in St. Petersburg it is broadcast on 586 and 666 MHz. The calculation formula will be as follows: L R = 300/f, where L R is the length of the loop (the result is presented in meters), and f is the average frequency range, for St. Petersburg this value will be 626 (the sum of 586 and 666 divided by 2). Now we calculate L R, 300/626 = 0.48, which means the length of the loop should be 48 centimeters.

If you take a thick RG-6 cable with braided foil, it can be used instead of copper wire to make a loop.

Now let's tell you how the structure is assembled:

A piece of copper wire (or RG6 cable) with a length equal to L R is measured and cut.
A loop of suitable diameter is folded, after which a cable leading to the receiver is soldered to its ends. If RG6 is used instead of copper wire, then the insulation from its ends is first removed, approximately 1-1.5 cm (the central core does not need to be cleaned, it is not involved in the process).
The loop is installed on the stand.
The F connector (plug) is screwed onto the cable to the receiver.

Note that despite the simplicity of the design, it is most effective for receiving “digits”, provided that the calculations are carried out correctly.

Do-it-yourself MV and UHF indoor antenna

If, in addition to UHF, there is a desire to receive MF, you can assemble a simple multiwave oven, its drawing with dimensions is presented below.

To amplify the signal, this design uses a ready-made SWA 9 unit; if you have problems purchasing it, you can use a homemade device, the diagram of which was shown above (see Fig. 2).

It is important to maintain the angle between the petals; going beyond the specified range significantly affects the quality of the “picture”.

Despite the fact that such a device is much simpler than a log-periodic design with a wave channel, it nevertheless shows good results if the signal is of sufficient power.

DIY figure eight antenna for digital TV

Let's consider another common design option for receiving “digits”. It is based on the classic scheme for the UHF range, which, because of its shape, is called “Figure Eight” or “Zigzag”.

Rice. 6. Sketch and implementation of the digital eight

Design dimensions:

outer sides of the diamond (A) – 140 mm;
inner sides (B) – 130 mm;
distance to the reflector (C) – from 110 to 130 mm;
width (D) – 300 mm;
the pitch between the rods (E) is from 8 to 25 mm.

The cable connection location is at points 1 and 2. The material requirements are the same as for the “Rhombus” design, which was described at the beginning of the article.

Homemade antenna for DBT T2

Actually, all of the examples listed above are capable of receiving DBT T2, but for variety we will present a sketch of another design, popularly called “Butterfly”.

The material can be used as plates made of copper, brass, aluminum or duralumin. If the structure is planned to be installed outdoors, then the last two options are not suitable.

Bottom line: which option to choose?

Oddly enough, the simplest option is the most effective, so the “loop” is best suited for receiving a “digit” (Fig. 4). But, if you need to receive other channels in the UHF range, then it is better to stop at “Zigzag” (Fig. 6).

The antenna for the TV should be directed towards the nearest active repeater, in order to select the desired position, you should rotate the structure until the signal strength is satisfactory.

If, despite the presence of an amplifier and reflector, the quality of the “picture” leaves much to be desired, you can try installing the structure on a mast.

In this case, it is necessary to install lightning protection, but this is a topic for another article.