General overview of delta television antennas. Antennas for TV at the dacha

All-wave remote antennas such as "Delta" do an excellent job of transmitting signals over a wide range of frequencies in various conditions. Typically, city residents need television antennas to broadcast over-the-air TV channels in order to provide the signal as free as possible from interference. As a rule, the structurally simple all-wave television antenna “Delta” consists of symmetrically located meter antennas and a decimeter antenna. Television antennas are installed outside the premises - on facades, roofs, windows or balconies. It is successful to use “Delta” television antennas in dachas, in village houses, in areas of not only reliable, but also insufficiently good reception, for which you can select a specific “Delta” model of the required power, if necessary, with a built-in amplifier.

Attention! Outdoor DVB-T2 antennas can be found in the section Outdoor antennas for digital television

Features of Delta antennas

Our offer includes television antennas in various designs. These are well-known Russian manufacturers of high-quality television antenna systems, whose products are in demand not only in Russia, but also outside our country. The TVdelta company presents passive and active (with amplifier) antennas from the Delta, Locus and other manufacturers, designed for operation in all weather conditions, in the temperature range from -40 to +50 degrees. To protect from bad weather, Delta antennas, made of steel or light aluminum, are coated with special powder paints.

In most options TV antennas "Delta" are supplied with all components for their installation or partially assembled, so you will not have any problems with installing such a television antenna. In conditions where it is necessary to install the Delta antenna at a certain height, for example, in a country house, masts of the required length are used; they are purchased separately. You can select these additional components for the antenna in our store. You can choose the “Delta” television antenna that is right for you after familiarizing yourself with its characteristics in our company’s catalog.

We are so accustomed to the flow of information that without it we feel insecure. That’s why, outside the city, having more or less equipped a house, the first thing that appears is a television. And for it to work in rural areas, you need a television antenna for your dacha. It is selected depending on the location of the nearest repeater - television tower and the type of television signal that you will “catch”.

Today there are several types of signals, and accordingly, the same number of types of antennas:

Terrestrial TV antenna: what to choose for your dacha

You can say exactly which antenna to install at your dacha only in relation to each specific case. When choosing, take into account:

location - plain, hill, lowland;
the presence or absence of forests and large trees near the house;
distance to the nearest repeater.

The main importance is the distance to the TV tower and which one. height you can raise the antenna. Sometimes every meter matters.

Indoor or outdoor

Indoor antennas can only be installed if the repeater is in your direct line of sight. If you can see a TV tower from your summer cottage, you can try it. In order not to waste money, you can make the most simple antenna with your own hands: take a piece of wire, connect it to the corresponding connector on the TV, and walk around the room with this “antenna”, climb higher to the ceiling, closer to the window, etc. If at least some signals are caught, you can try or buy.

Outdoor antennas “catch” tens of kilometers from repeaters

If during all your movements there are no signs of a clear signal, you need an outdoor antenna, but for a reliable reception area (with lower gain). For all other cases, when the distance to the tower is tens of kilometers, an external antenna is definitely needed.

Broadband or narrowband

Since terrestrial television is broadcast in two bands - decimeter and meter, there are antennas for these bands. If the receiver “catch” a signal in only one band, they are called narrowband. They are only available for UHF or only for VHF frequencies.

There are also broadband (also called all-wave) - their design is designed so that it is possible to normally receive a signal at all frequencies. They are usually bulkier and heavier and have a long shaft. But they put up with this - a broadband television antenna for a dacha can “catch” more channels. That's why they buy them most often.

Active or passive

More attention should be paid to whether it is better to install an active or passive antenna. An active device is a device with an amplifier built into the housing. Passive ones are just hardware for which you need to buy an amplifier separately.

Active receivers with a built-in amplifier are cheaper, receive more channels, but they have a significant drawback: amplifier boards often break. Any more or less serious thunderstorm, and channels that were previously clearly received begin to “snow” or disappear altogether. Replacing the board can help the problem. To do this, you need to climb onto the roof, remove the antenna, change the board, install it again and configure it. This procedure can be repeated after each thunderstorm.

Even if thunderstorms did not affect the performance of your country antenna, still after a year and a half the number of well-received channels decreases. The quality gradually gets worse, and sooner or later, you notice that it is no longer possible to watch. The reason is oxidation of contacts and elements on the board. The receivers on the antenna are far from sealed and dust and moisture get inside, destroying the contacts and tracks. Therefore, the average lifespan of an active antenna is about a year. If it's not a thunderstorm, oxidation will finish it off.

The best antenna for a summer residence: inactive with a separate amplifier

There is nothing to help with a thunderstorm, and oxidation can be significantly slowed down if immediately after purchase, fill the board with silicone on both sides. This will protect contacts and elements from oxidation. No one will repair it anyway; if the board “flies”, you buy a new one and put it in its place. That's all the repairs. It is also useful to seal the cable connection point. Here, too, due to oxidation, there are large signal losses.

Passive antennas with separate amplifiers are good because the hardware is installed above the roof, and the amplifier is in the attic. Replacing a circuit board in the attic is much less of a hassle than replacing it on the roof. Especially in winter. They “catch” fewer channels, but the picture is “cleaner”.

There is one more plus: individual amplifiers have two adjustments - separately for the UHF range and for MV. This is useful, since sometimes some signals come with a much higher level and they “clog” weaker ones. Then there is an overlap of sound and/or image, in some cases, if some signal is very strong, it is completely “snowing”. By adjusting the sensitivity of the ranges you can save the situation. So passive antennas with separate amplifiers for the garden are the best choice.

Samsung and LG TVs generally have a “weak signal” function. In this case, you may not need an amplifier at all. Install a passive antenna at your dacha, turn on the mode, and tune in the channels. It should be good to show at least 5-6 channels.

To ground or not

Another problem that needs to be solved is whether the TV antenna for the dacha should be grounded. On the one hand, this is often the highest point. On the other hand, if it is grounded, it will catch any lightning strike that is nearby. Accordingly, you will have to change the board every time, as it will fail.

For this reason, “antenna specialists” insist that they do not need to be grounded. Especially if the device is located below the power wires. Lightning will then strike the highest grounded point. The main thing is that it is not your antenna.

Which antennas are better

As usual, in addition to the type of equipment, you have to choose a manufacturer. And this, perhaps, is no simpler. Recommendations can help. There are several popular manufacturers on the forums:

Locus (Locus). Antennas made in Russia. Wide range, low prices (from 480 rubles to 1.7 thousand rubles). There are both active ones - with a built-in amplifier, and passive ones.
Harpoon. Also a Russian-made antenna. Receives in UHF and MV zones. They are produced only in passive form and are intended for installation in areas of poor reception. Retail price - Harpoon-0416 - 1500 rubles, Harpoon-1028 - 2300 rubles.
Antennas "Delta" produced by JSC "NPP OST". The range here is very wide. There are both narrowly targeted only for VHF or only for UHF bands, and broadband ones. Moreover, UHF antennas can be used to receive a DVB-T2 digital television signal. Many models are equipped with an F-connector - a device through which the cable is connected: during installation, you do not need to disassemble it to connect it. Insert the conductor, stripped of insulation, into the socket. All. The cable is connected.
GoldMaster (GoldMaster). There are few reviews, but according to those available, it receives reliably even in the area of uncertain reception. Even during rain, the signal quality hardly drops. The picture is still clear, without “snow”.

All other manufacturers are not particularly popular.

For inactive antennas, amplifiers are also needed. There are also preferences here:

LHA House Amplifier;
TERRA (Terra);
Powerful amplifiers with low noise levels Breeze, Alcad.

Antenna installation

Before starting all work, it is useful to lubricate all screws, nuts, and antenna connections with Movil or Litol, something similar in properties. If an active antenna is selected, it is better to seal the board with silicone. After such treatment, the antenna will last not a year, but much longer.

About which cable to use for connection. It’s better not to try to save money here: the losses will be too great. Therefore, take branded SAT 50 or SAT 703. The “picture” depends no less on the quality of the cable and the quality of connections than on the reception.

TV antenna for a summer residence: where and how to install

The installation location is selected taking into account where you will need to point the antenna. If the roof and wind loads allow, it can be fixed to the roof. In order to raise the receiver higher, the antenna is mounted on a mast. There are special clamps for this.

In some cases, you have to raise the antenna as high as possible - in lowlands or if trees block reception. Then telescopic rods will come in handy

There are prefabricated metal masts, and there are telescopic - folding masts. This type is more convenient, especially if the antenna is with a receiver - you will need to change the board periodically, and completely dismantling the mast every time is a pleasure. Telescopic masts can be lowered by unscrewing the locking ring. The antenna attached to the top will lower along with the top of the boom.

If you don’t need to lift it high, you can use a wooden beam or a sanded trunk of a young pine tree. This is a completely dacha option. You can use a steel pipe of not very large diameter or a corner. There are a lot of options. Selected support needs to be secured. Mounting methods are shown in the figure.

The most common antenna mount is on the pediment. It is the easiest to implement, but only if the decoration or material of the walls allows it. This is not how they are mounted on walls covered with siding, and it is too complicated. Then the option is to fasten the rod to the pipe, to the rafters, or on guy wires to the roofing material.

When attaching to the gable, the distance between the fasteners must be at least 1.5 meters. If none of these methods can be implemented for some reason, you can try to install the antenna on a powerful tree growing nearby. You can attach the antenna to the trunk and trim branches that interfere with reception. Sometimes this is the best way.

Cable fastening

When installing the antenna, the cable is lowered down along the rod. It is secured with clamps every 50-80 cm. Having lowered the cable to the level of the roofing material, it is led along the ridge (so that it is not torn off by the snow) to a bracket, with the help of which it is lowered from the roof. The bracket is mounted above the window near the TV. The cable is brought into the room through a hole in the window frame. With an upward slope, drill a hole with a slightly larger diameter than the diameter of the cable. This will prevent raindrops from getting inside the frame. The cable in front of the frame should sag slightly - this gives freedom to temperature changes.

If the television antenna for the dacha is inactive, the amplifier is installed in the attic, the cable from the antenna is led to it, and from the amplifier to the TV.

One tip: when laying, you need to avoid sharp bends. The minimum radius is at least 5 cable diameters. When fastening with staples, do not pinch it.

Watch the video to see how to cut and connect antenna cables.

V. DAVYDOV (UW9WR), UfaThe disadvantage of the previously described electronic switches antennas is a significant attenuation in the receiving mode, reaching 45-50% (especially in the ranges of 21 and 28 MHz). Switch, scheme which is shown in the figure, provides an attenuation of no more than 10%. When manufacturing the switch, it is necessary to isolate the body of the output capacitor of the P-circuit (in the diagram - C4) from the chassis with a fluoroplastic or polystyrene gasket 5 mm thick. The antenna is connected to the Gn1 socket, the receiver input - to nest GN2.RADIO No. 7, 1975 p.15...

For the scheme "MINIATURE DIRECTIONAL ANTENNA FOR 144-146 MHz RANGE"

For the "ALL METAL DELTA ANTENNA" circuit

For the diagram "Double square antenna design"

For the "DUAL BAND UHF ANTENNA" circuit

For the "144 MHz VERTICAL ANTENNA" circuit

For the circuit "Antenna amplifier for a radio transmitter"

RF power amplifiersAntenna amplifier for radio transmitter Scheme The antenna amplifier does not require any special explanation. The amplifier is mounted in a casing made of galvanized metal 1 mm thick, dimensions 120x60x30 mm. An aluminum plate of the same size, 10 mm thick, is screwed to the bottom of the body. The design of the printed circuit board is the same as in [Z]. The drawing is not shown here, because The board configuration is highly dependent on the type of parts used. It is only important that all connections are as short as possible and reliable thermal contact of transistor VT1 with the heatsink plate is ensured. Details. Relay K1, K2 - RES-15(002). Connectors XW1, XW2 - SR-50-73F. Resistors - MLT. Capacitors - CT, KM; S16.S17-KPK-MP. Inductors: LI - inductor DPMZ-3 10 μH; L2 - 14 turns on a resistor MLT-0.5 150 Ohm PEV-2 0.35 turn to turn. L9, L11 -DPM1-0.1 56 µH. The remaining coils are frameless, wound with PEV-2 0.8 wire on a 5.5 mm mandrel. The number of turns depending on the range is given in the table. The same table shows the capacitances SZ...S15 (pF). RangeL3L4L516L718L1C3С4С5С7С8С9С10С11С12С14С1527. ..29 MHz346999856047011068470200...27027027011Q682750 Hz23577763302706839270120...150150150683915 Setting up the antenna unit is contained in the settings using C16, C17 input circuit of the antenna amplifier for maximum reception sensitivity nickname of the radio station. By connecting an HF generator to input A5...

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 penetrates 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 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:

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.

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 in the same place 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:

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.

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.

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. Firstly, the “belt” amplifiers are broadband, low-noise. 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.