It is correct to install the antenna amplifier directly next to the antenna, since the signal coming from the antenna along the antenna cable gradually fades. And sometimes, especially in conditions of long-distance reception, an antenna amplifier installed next to the TV is no longer useful.
Also, with the use of an antenna amplifier at the input of the feeder, it becomes possible to branch the signal to several TVs without deteriorating the signal-to-noise ratio and, as a result, a good picture on the TV screen.
You should try to install antenna amplifiers as close to the antenna as possible; power supply to the amplifier is carried out via the coaxial cable of the feeder through the decoupling in accordance with the diagram below:
The 12 volt power supply for the circuit can be taken from any suitable adapter or. Two-stage antenna amplifiers consume a current of no more than 50 mA, so the power of the adapter should not exceed 5-10 W.
Diodes D1,2 protect the transistor stages of the amplifier, assembled according to a circuit with a common emitter, from damage during a thunderstorm. R1,3 carry out temperature correction of transistor modes. The gain of this antenna amplifier is 30 dB, and the current consumption is only 12 mA. L1 - PEV-2 with a diameter of 0.8 mm, 2.5 turns wound on a mandrel with a diameter of 4 mm
The circuit is built on two transistors of different conductivity, connected according to a circuit with a common emitter and a common base. Using this particular connection reduces the noise figure of the antenna amplifier. Smooth adjustment of the device in frequency can be done using tuning capacitor C7, which is part of the oscillating circuit.
The input circuit is made of radio components L1, C1, L2, C1 and is a high-frequency filter with a frequency of about 48.5 MHz band I and around 160 MHz band II. Resistances R1 and R2 select the operating mode of the first transistor. By selecting the value of these resistors, it is necessary to obtain a voltage at the collector of about 5V at a current of 5 mA. Then the noise level of the amplifier will not be higher than 4.7 dB at a frequency of 400 MHz.
The operating mode of the second transistor is set by the values of resistors RЗ and R5. The resistance of these resistors must be selected such that the voltage at the collector junction of the transistor is around 10V at an emitter current of 1mA. With these parameters, the gain of the second stage will be about 14 dB with a frequency of 8 MHz. To reduce the voltage ripple of the power supply, capacitors C4 and C8 are used in the antenna amplifier.
Setting up and adjusting the amplifier consists of checking the operating modes of the transistors for direct current. Tuning to the desired television channel is carried out using trimmer capacitor C7. Stretching or compressing the turns of coils L1, L2 and L3, L4 regulates the cutoff of high and low frequencies.
This antenna amplifier has a gain of 10 to 15 dB in the frequency range 400 - 850 MHz. Capacitors C1, C2, C6, C7 SMD for surface mounting, when using conventional ones, the gain drops by 30%. The antenna amplifier must be placed in a metal shielding housing.
The amplifier is powered by a 12 volt power supply. The amplifier is configured by changing the resistance of resistor P1 and adjusting it according to the picture on the TV screen.
Figure 1 shows a simple amplifier SWA-36 from TELTAD, and in the figure two amplifiers SWA-49 (analogous to SWA-9) from ANPREL
The SWA-36 amplifier consists of two amplification stages made using transistors VT1 and VT2. The signal from the antenna passes through a matching transformer (not shown in the diagram) and capacitor C1 to the base of transistor VT1. The operating point of the transistor is determined by the resistance of resistor R1.
The negative voltage feedback that operates in this case linearizes the characteristic of the first stage, stabilizes the position of the operating point, but slightly reduces its gain. Frequency correction is not applied in the first stage. The second amplifier stage is also assembled according to a circuit with OE and negative feedback in voltage through resistors R2 and R3, but it also has a current negative feedback through R4, which strictly stabilizes the operating mode of transistor VT2.
To avoid a large loss in gain, resistor R4 is shunted across the variable component by capacitor SZ, the capacitance of which is about 10 pF. As a result, at low frequencies the capacitance of the capacitor is high and the resulting negative AC feedback reduces the gain, correcting the frequency response of the antenna amplifier. The SWA-36 amplifier also has disadvantages - these are passive losses in the output circuit on resistor R5.
The SWA-49 amplifier has a similar circuit, which also consists of two stages using transistors with a common emitter. But unlike the SWA-36, it has good isolation of the supply circuits through L-shaped filters L1C6, R5C4 and a higher gain.
As you can see, the antenna amplifier circuit is so simple that there is nothing to configure in it, provided that you have soldered it correctly.
Kirill Sysoev
Calloused hands never get bored!
Content
The device is used to improve the quality of reception of television channels on the antenna. As a rule, amplifiers are used in the decimeter or meter range, but they can also be installed at a considerable distance from the receiver.
To increase the signal reception level of the antenna, an amplifier is connected to it. It is useful in cases where the distance from the television center to the receiver is significant or the wrong model of cable or satellite antenna is selected. Using the device you can significantly improve the quality of the picture shown on your TV. It is considered correct to install this device directly next to the receiver, since the signal coming from it along the cable gradually decreases. In conditions of long-distance reception, however, an amplifier located nearby will be of no use.
TV antenna amplifiers have different parameters and can be broadband, multi-band, or range. In addition, excellent types of devices are designed for long-range and short-range reception, and are installed next to outdoor and indoor receivers. Distinctive features of different types of devices:
The modern market presents many different models, for this reason, many people find it difficult to decide which device suits them best. To make the right choice, you should consider several important parameters:
A huge selection of devices that improve the signal of television receivers is presented in online stores, points of sale of electronics, and hypermarkets with corresponding departments. The price of these devices varies greatly and depends not only on the parameters, but also on the regions where the TV antenna amplifier is sold. Average cost of popular models:
An indoor antenna with an amplifier allows you to provide a better picture on the TV screen, minimize noise and find more channels. At the same time, it is not necessary to buy a device, because it is not very difficult to make it yourself using beer cans. An amplifier for a TV antenna of this type can be made in 10-15 minutes and functions perfectly. To create it you need:
Scheme for creating a device for dvb:
Since television channels are in the UHF range, there is no need for balancing. The characteristic impedance of the half-wave vibrator is between 72 and 76 Ohms, which is in excellent agreement with the cable. To configure the receiver, you must adjust the distance between the banks. As the diameter of the wire (can) increases, the signal bandwidth will increase.
Recently, local commercial television channels have appeared in many cities, operating mainly on UHF, but often on MB. However, due to the low power of inexpensive television transmitters, the specifics of UHF propagation and many other factors (the height of the transmitting antenna, its design, terrain), the reliable reception zone of such television transmitters is only a few kilometers.
In this case, TV viewers living on the outskirts of the city suffer especially hard, since the TV transmitter is usually installed in the city center. To ensure decent reception quality, it is necessary to use complex antennas tuned to a specific channel and low-noise antenna amplifiers. Residents of rural areas face the same problems.
The proposed antenna amplifier is designed for operation in such conditions; it is easy to manufacture and configure and has such characteristics:
1. The unevenness of the frequency response throughout the entire television range is no more than....................... 3 dB.
2. Gain.................................... 12 dB.
3. Input impedance......... 75 Ohm.
4. Output impedance................... 75 Ohm.
5. Supply voltage........................... +12V.
6. Current consumption no more than ............. 15 mA.
The circuit diagram of the amplifier is shown in the figure. The amplifier is broadband; there are no resonant circuits at its input. The signal from the antenna is fed to the input of the amplifier, the input impedance of which is reduced to 75 Ohms using resistor R1. Diodes VD1 and VD2 serve to protect the amplifier input from static discharges that can penetrate through the antenna.
The amplifier is two-stage, both amplification stages are built according to a circuit with a common emitter and capacitive coupling between the stages. Stabilization of transistor modes for direct current is carried out using negative feedback through resistors R2 and R5.
This stabilization allows the emitters of the transistors to be connected directly to the common wire, which ensures a high stable gain of the cascades. Low load resistances of the cascades (resistors R3 and R6) eliminate the possibility of self-excitation of the amplifier at low frequencies.
The amplifier is powered directly from the +12V power supply of the USST TV. The possibility of power supply from a separate network adapter is not excluded. In any case, power is supplied via a separate shielded cable, which is connected to the +12V connector. The amplifier is located close to the antenna, so the length of the power cable is equal to the length of the cable going to the antenna socket of the TV.
The amplifier is mounted in a housing soldered from brass plates or tin. The case has dimensions 50x70x20 mm. The cascades are located along the body according to the schematic diagram. At one end there is a connector for connecting an antenna, at the opposite end there are two connectors, one for connecting a cable from the antenna socket of the TV, and the other for supplying power.
Setting up the antenna amplifier consists of setting the collector currents of the transistors by selecting the values of resistors R2 and R5, the collector current VT1 is 3 mA, the collector VT2 = 5 mA.
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.
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.
In accordance with the new reception conditions, the basic requirements for TV antennas have also changed:
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:
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.
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.
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.
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):
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.
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.
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.
An all-wave (more precisely, frequency-independent, FNA) antenna is shown in Fig. It consists of two triangular metal plates, two wooden slats, and a lot of enameled copper wires. The diameter of the wire does not matter, and the distance between the ends of the wires on the slats is 20-30 mm. The gap between the plates to which the other ends of the wires are soldered is 10 mm.
Note: Instead of two metal plates, it is better to take a square of one-sided foil fiberglass with triangles cut out of copper.
The width of the antenna is equal to its height, the opening angle of the blades is 90 degrees. The cable routing diagram is shown there in Fig. The point marked in yellow is the point of quasi-zero potential. There is no need to solder the cable braid to the fabric in it, just tie it tightly, and the capacity between the braid and the fabric will be enough for matching.
The CHNA, stretched in a window 1.5 m wide, receives all meter and DCM channels from almost all directions, except for a dip of about 15 degrees in the plane of the canvas. This is its advantage in places where it is possible to receive signals from different television centers; it does not need to be rotated. Disadvantages - single gain and zero gain, therefore, in the interference zone and outside the zone of reliable reception, the CNA is not suitable.
Note : There are other types of CNA, for example. in the form of a two-turn logarithmic spiral. It is more compact than the CNA made of triangular sheets in the same frequency range, therefore it is sometimes used in technology. But in everyday life this does not provide any advantages, it is more difficult to make a spiral CNA, and it is more difficult to coordinate with a coaxial cable, so we are not considering it.
Based on the CHNA, the once very popular fan vibrator (horns, flyer, slingshot) was created, see fig. Its directivity factor and coefficient of performance are something around 1.4 with a fairly smooth frequency response and linear phase response, so it would be suitable for digital use even now. But - it works only on HF (channels 1-12), and digital broadcasting is on UHF. However, in the countryside, with an elevation of 10-12 m, it may be suitable for receiving an analogue. Mast 2 can be made of any material, but fastening strips 1 are made of a good non-wetting dielectric: fiberglass or fluoroplastic with a thickness of at least 10 mm.
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.
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:
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:
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.
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.
If the UHF LPA is consistent with the cable amplifier (see below, about Polish antennas), then the arms of a meter dipole, linear or fan-shaped, like a “slingshot”, can be attached to the line. Then we will get a universal VHF-UHF antenna of excellent quality. This solution is used in the popular Delta antenna, see fig.
Antenna “Delta”
A Z-antenna with a reflector gives the same gain and gain as the LPA, but its main lobe is more than twice as wide horizontally. This can be important in rural areas when there is TV reception from different directions. And the decimeter Z-antenna has small dimensions, which is essential for indoor reception. But its operating range is theoretically not unlimited; frequency overlap while maintaining parameters acceptable for the digital range is up to 2.7.
The design of the MV Z-antenna is shown in Fig; The cable route is highlighted in red. There in the lower left there is a more compact ring version, colloquially known as a “spider”. It clearly shows that the Z-antenna was born as a combination of a CNA with a range vibrator; There is also something of a rhombic antenna in it, which does not fit into the theme. Yes, the “spider” ring does not have to be wooden, it can be a metal hoop. "Spider" receives 1-12 MV channels; The pattern without a reflector is almost circular.
The classic zigzag works either on 1-5 or 6-12 channels, but for its manufacture you only need wooden slats, enameled copper wire with d = 0.6-1.2 mm and several scraps of foil fiberglass, so we give the dimensions in fraction for 1-5/6-12 channels: A = 3400/950 mm, B, C = 1700/450 mm, b = 100/28 mm, B = 300/100 mm. At point E there is zero potential; here you need to solder the braid to a metallized support plate. Reflector dimensions, also 1-5/6-12: A = 620/175 mm, B = 300/130 mm, D = 3200/900 mm.
The range Z-antenna with a reflector gives a gain of 12 dB, tuned to one channel - 26 dB. To build a single-channel one based on a band zigzag, you need to take the side of the square of the canvas in the middle of its width at a quarter of the wavelength and recalculate all other dimensions proportionally.
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.
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:
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.
Many users have Polish antennas, which previously received analogue decently, but refuse to accept digital - they break or even disappear completely. The reason, I beg your pardon, is the obscene commercial approach to electrodynamics. Sometimes I feel ashamed for my colleagues who have concocted such a “miracle”: the frequency response and phase response resemble either a psoriasis hedgehog or a horse’s comb with broken teeth.
The only good thing about the Poles is their antenna amplifiers. Actually, they do not allow these products to die ingloriously. Belt amplifiers are, firstly, low-noise, broadband. And, more importantly, with a high-impedance input. This allows, at the same strength of the EMF signal on the air, to supply several times more power to the tuner input, which makes it possible for the electronics to “rip out” a number from very ugly noise. In addition, due to the high input impedance, the Polish amplifier is an ideal USS for any antennas: whatever you attach to the input, the output is exactly 75 Ohms without reflection or creep.
However, with a very poor signal, outside the zone of reliable reception, the Polish amplifier no longer works. Power is supplied to it via a cable, and power decoupling takes away 2-3 dB of the signal-to-noise ratio, which may not be enough for the digital signal to go right into the outback. Here you need a good TV signal amplifier with separate power supply. It will most likely be located near the tuner, and the control system for the antenna, if required, will have to be made separately.
The circuit of such an amplifier, which has shown almost 100% repeatability even when implemented by novice radio amateurs, is shown in Fig. Gain adjustment – potentiometer P1. The decoupling chokes L3 and L4 are standard purchased ones. Coils L1 and L2 are made according to the dimensions in the wiring diagram on the right. They are part of signal bandpass filters, so small deviations in their inductance are not critical.
However, the installation topology (configuration) must be observed exactly! And in the same way, a metal shield is required, separating the output circuits from the other circuit.
We hope that experienced craftsmen will find some useful information in this article. And for beginners who don’t yet feel the air, it’s best to start with a beer antenna. The author of the article, by no means an amateur in this field, was quite surprised at one time: the simplest “pub” with ferrite matching, as it turned out, takes the MV no worse than the proven “slingshot”. And what it costs to do both - see the text.
(2
ratings, average: 4,00
out of 5)
Said):
And on the roof there was a satisfactory reception for Polyachka. I’m 70–80 kilometers from the television center. These are the problems I have. From the balcony you can catch 3-4 pieces from 30 channels, and then with “cubes”. Sometimes I watch TV channels from the Internet on the computer in my room, but my wife cannot watch her favorite channels normally on her TV. Neighbors advise installing cable, but you have to pay for it every month, and I already pay for the Internet, and my pension is not flexible. We keep pulling and pulling and there’s not enough for everything.
Pyotr Kopitonenko said:
It’s not possible to install an antenna on the roof of the house; the neighbors swear that I walk around and break the roofing material covering and then their ceiling leaks. Actually, I am very “grateful” to that economist who received a prize for saving money. He came up with the idea of removing the expensive gable roof from the houses and replacing it with a flat roof covered with poor roofing material. The economist received money for saving, and the people on the top floors now suffer all their lives. Water flows on their heads and on their beds. They change the roofing felt every year, but it becomes unusable within a season. In frosty weather, it cracks and rainwater and snow flow into the apartment, even if no one walks on the roof!!!
Sergey said:
Greetings!
Thanks for the article, who is the author (I don’t see the signature)?
The LPA works perfectly according to the above method, UHF channels 30 and 58. Tested in the city (reflected signal) and outside the city, distances to the transmitter (1 kW) respectively: 2 and 12 km approximately. Practice has shown that there is no urgent need for the “B1” dipole, but another dipole before the shortest one has a significant effect, judging by the signal intensity in %. Especially in city conditions, where you need to catch (in my case) the reflected signal. Only I made an antenna with a “short circuit”, it turned out that way, there was simply no suitable insulator.
In general, I recommend it.
Vasily said:
IMHO: people looking for an antenna to receive digital TV, forget about the LPA. These wide-range antennas were created in the second half of the 50s (!!) of the last century in order to catch foreign television centers while on the shores of the Soviet Baltic states. In magazines of the time, this was bashfully called “extra-long-range reception.” Well, we really loved watching Swedish porn at night on the Riga seaside...
In terms of purpose, I can say the same about “double, triple, etc. squares”, as well as any “zigzags”.
Compared to a “wave channel” of similar range and gain, LPAs are more bulky and material-intensive. Calculating the LPA is complex, intricate and more like fortune telling and adjusting the results.
If in your region ECTV is broadcast on neighboring UHF channels (I have 37-38), then the best solution is to find a book online: Kapchinsky L.M. Television antennas (2nd edition, 1979) and make a “wave channel” for a group of UHF channels (if you broadcast above 21-41 channels, you will have to recalculate) described on page 67 et seq. (Fig. 39, Table 11).
If the transmitter is 15 - 30 km away, the antenna can be simplified by making it four - five element, simply without installing directors D, E and Zh.
For very close transmitters, I recommend indoor antennas; by the way, in the same book on pp. 106 – 109 there are drawings of wide-range indoor “wave channel” and LPA. The “wave channel” is visually smaller, simpler and sleeker with higher gain!
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Despite the rapid development of the Internet, television remains the main source of information for the majority of the population. But in order for your TV to have a high-quality picture, you need a good antenna. It is not at all necessary to buy a television antenna in a store, because you can make it yourself and save a lot of money.
You can find out how to make high-quality antennas for various broadcast bands and what materials to use by reading our article.
There are many types and forms of television antennas, the main ones are listed below:
The whole world, including our country, has switched from analogue to digital broadcasting. Therefore, when making an antenna with your own hands or buying it in a store, you need to know which antenna is best suited for receiving DVB-T2 format:
If you live not far from a TV tower, then you can easily make a simple antenna for receiving a signal in DVB-T2 format with your own hands:
The antenna is ready! It should be noted that such a primitive antenna is not capable of providing a high-quality and stable signal at a distance from the TV tower and in places with sources of interference.
Let's look at several options for television antennas that you can make yourself from scrap materials:
An antenna from beer cans can be made in literally half an hour, using the materials you have on hand. Of course, such an antenna will not provide a super-stable signal, but for temporary use in a country house or in a rented apartment it is quite suitable. 
Beer can antenna
To make an antenna you will need:
After making sure that you have all the above items in stock, do the following:
There are other variations of this antenna, with four and even eight banks, but no obvious effect of the number of banks on the signal quality has been identified.
You can also learn how to make an antenna from beer cans from the video:
The antenna received its name in 1961, after the name of its inventor Kharchenko K.P., who proposed using zigzag-shaped antennas to receive television broadcasts. This antenna is very well suited for receiving digital signals. 
Antenna Kharchenko
To make a zigzag antenna you will need:
First you need to make an antenna frame. To do this, take the wire and cut off a piece of 109 centimeters. Next, we bend the wire so that we get a frame of two parallel rhombuses, each side of the rhombus should be 13.5 centimeters, make loops from the remaining centimeter to fasten the wire. Using a soldering iron and solder, connect the ends of the wire and close the frame.
Take the cable and strip its end so that you can solder the rod and cable shield to the frame. Next, solder the rod and cable shield in the center of the frame. Please note that the screen and the rod should not touch.
Place the frame on the base. The distance between the corners of the frame at the junction with the cable should be two centimeters. Make the size of the base approximately 10 by 10 centimeters.
Strip the other end of the cable and install the plug.
If necessary, attach the antenna base to a stand for further installation on the roof.
You can watch more detailed instructions for making the Kharchenko antenna in the video:
To make the antenna you will need a 75 ohm coaxial cable with a standard connector. To calculate the cable length required for the antenna, you need to find out the digital broadcasting frequency and divide it in megahertz by 7500, and round the resulting amount. 
Cable antenna
Once you have the cable length, do the following:
You can visually consolidate the information by watching the video:
It’s worth mentioning right away that to receive a satellite signal you need a tuner and a special set-top box. Therefore, if you do not have this equipment, then creating a satellite dish with your own hands will not be possible, since you yourself can only make a parabolic reflector:
All of the methods listed above can be considered seriously only out of sporting interest, since making a parabolic reflector by hand is a very labor-intensive and expensive process. In addition, it is very difficult to accurately calculate the parameters of a satellite dish at home. Therefore, we advise you not to be original and buy a complete satellite dish.
If the place where you live has a weak television signal and a conventional antenna cannot provide a high-quality picture on your TV, then an antenna amplifier can help in this situation. You can make it yourself if you have a little knowledge of radio electronics and know how to solder. 
Amplifiers should be installed as close to the antenna as possible. It is better to power the antenna amplifier via a coaxial cable through a decoupler. 
Isolation power circuit
The decoupler is installed at the bottom of the TV and is supplied with 12 volt power from the adapter. Two-stage amplifiers consume a current of no more than 50 milliamps; for this reason, the power of the power supply should not exceed 10 watts.
All connections of the antenna amplifier on the mast must be made by soldering, since the installation of mechanical connections will lead to their corrosion and rupture during further operation in an aggressive external environment.
There are times when you have to receive and amplify a weak signal in the presence of powerful signals from other sources. In this case, both weak and strong signals arrive at the amplifier input. This leads to blocking the operation of the amplifier or switching it to a non-linear mode, mixing both signals, which is expressed in the overlay of the image from one channel to another. Reducing the amplifier supply voltage will help correct the situation.
Please note that UHF amplifiers are greatly influenced by signals in the meter range. To weaken the impact of meter signals, a high-pass filter is placed in front of the UHF amplifier, which blocks meter waves and transmits only signals in the decimeter range.
Below is a diagram of a VHF antenna amplifier:
We also suggest that you familiarize yourself with the circuit of the decimeter amplifier:
You can see the operating principle of the antenna amplifier in the video:
We hope that our article about television antennas was useful to you!
