5.1. FEATURES OF LONG RECEPTION

The main feature of long-range reception of television broadcasts is the low level of the field strength of the received signal due to the large distance between the transmitting and receiving antennas in the far part of the line of sight and because of shading by the earth's surface beyond the border of the line of sight - in the penumbra. With distance from the transmitter, the field strength decreases monotonically, but in the penumbra zone, this decrease becomes sharper. In the line of sight, an increase in the distance from the transmitter is accompanied by a decrease in the signal power flux density (the density of the field lines decreases) simply because the circumference increases with an increase in its radius. Beyond the line of sight, field strength is determined almost exclusively by diffraction and normal refraction of radio waves.

Another feature of long-range reception is the presence of interference from other television transmitters operating on the same or adjacent frequency channel. To mitigate such interference, the current regulations establish the minimum distances between the transmitters:

about 500 km between transmitters operating on identical channels, and about 300 km between transmitters operating on adjacent frequency channels. Nevertheless, in conditions of long-range reception, such interference does occur and special measures have to be used to mitigate it.

In conditions of long-range reception, the weather has a strong influence on the level of field strength. In the case of fog, rain or snow, the absorption of signal energy in space increases sharply, especially in the decimeter wavelength range, and sometimes it becomes impossible to receive it at all.

The surface on the path over which the signal propagates is important. Continuous and extended forests worsen the propagation conditions; over the plain, swamps and especially over the sea, the signal spreads better. The conditions for receiving television broadcasts in mountainous conditions are very poor, where the boundaries of the line of sight do not depend on the distance to the transmitter, but are entirely determined by the local relief. Naturally, there are hills and valleys on flat terrain as well. Moreover, even at a relatively close distance from the transmitter, when the receiving point is located in a valley, the field strength can be quite low. Therefore, you cannot focus solely on the distance to the TV center or repeater, but you should take into account the terrain.

One of the features of long-range reception is the presence of signal fading, that is, regular changes in field strength. In the penumbra, where the level of field strength is highly dependent on normal refraction,

daily and seasonal changes in field strength are observed. In clear weather in the daytime, the refraction of radio waves increases and the field strength increases. As a rule, the field strength also increases in summer. Such slow fading is especially noticeable on high-frequency channels: in the range of 6-12 channels and in the decimeter range. In addition to slow ones, fast fading is also observed, the period of which does not exceed an hour. Such fading is associated with the presence of local disturbances of the atmosphere along the route during gusts of wind, the presence of separate clouds, or, conversely, gaps in continuous clouds. Fast fading in conditions of long-range reception are quite deep, sometimes the field strength can change tens of times.

The low level of the signal field strength in conditions of long-range television reception dictates the need to install a highly efficient antenna with a high gain, since the received signal voltage at the antenna output is determined by the product of the field strength and the antenna gain. Due to the fact that the radius of the line of sight is determined by the height of the receiving antenna, in the far part of the line of sight and in the penumbra, the field strength at the receiving point depends on the height of the antenna, and this dependence turns out to be approximately proportional: when the height of the antenna mast is doubled the field strength also doubles. Therefore, it is always advisable to use the antenna mast as high as possible. Installing a high gain receiving antenna on a high mast will increase the signal voltage at the antenna output both at a steady level of field strength and in fading conditions.

To combat signal fading, all radio receivers, broadcasting and television, are equipped with an automatic gain control AGC system, which reduces the gain of the receiving path when the signal at the input increases and increases the gain when it decreases. However, the AGC system is able to withstand fading only when the minimum signal is still greater than the receiver sensitivity threshold. This level of signal voltage at the input of the television receiver must be provided by the used antenna.

5.2. WAVE CHANNEL MULTI-ELEMENT ANTENNAS

5.2. WAVE CHANNEL MULTI-ELEMENT ANTENNAS

Earlier, the advantages and disadvantages of multi-element antennas of the "Wave channel" type have already been considered, and it was not recommended to manufacture such antennas in amateur conditions. In conditions of long-range reception, it is permissible to use multi-element "Wave Channel" antennas of industrial production. Then there is the possibility that the antenna is factory tuned.

In the radio amateur literature, descriptions of the designs of self-made multi-element "Wave Channel" antennas are often published, their gain factors are given and such antennas are recommended for use in long-range reception conditions. Without questioning the results obtained by the authors of these designs, I would like to replace

It should be noted that an assessment of the suitability of a particular antenna design can be made only by repeating this design many times, and not by a single result. The responses of radio amateurs who tried to make and install such antennas, in most cases, turn out to be negative, which indicates the poor repeatability of these antenna designs. In addition, it should be taken into account that by no means all experiments on the creation of multi-element antennas end with corresponding publications. Naturally, in those cases when poor results were obtained, they were not reflected in the literature. At the same time, according to numerous responses, the repeatability of loop antennas turns out to be very high, and the gain of these antennas is much higher. This forces us to recommend using loop antennas instead of Wave Channel antennas in long-range reception conditions.

5.3. MYTHS ABOUT WONDERFUL ANTENNAS

5. 3. MYTHS ABOUT "WONDERFUL" ANTENNAS

Television antennas designed for long-range reception of transmissions, as a rule, are large and relatively complex in design. Antennas designed to receive a signal through the first and second frequency channels, which are the longest wavelengths in the range allocated for television, have especially large dimensions. Therefore, every fan of long-range television reception strives to find such an antenna design that would have a high gain and at the same time have minimal dimensions and the simplest design... Such requirements are contradictory and cannot be met, since in nature you have to "pay" for everything: in this case, you have to pay for an increase in the gain by increasing the size of the antenna. In addition, a natural objection arises: if it were possible to create such an antenna, who would build large antennas?

Nevertheless, incorrect demand generates corresponding supply. Therefore, from time to time in the periodicals there are articles with descriptions of miraculous antennas that make it possible to obtain reliable reception of television broadcasts at very large distances from the television center with small sizes and simple antenna designs. Some antenna designs contain liquid mercury or metal filings. Such messages are caused by delusion or bad faith of the authors of the articles and the technical illiteracy of the editors. Due to the surface effect, the high-frequency currents of the signal received by the antenna flow exclusively over the thinnest surface layer of the antenna metal, the thickness of which does not exceed hundredths of a millimeter. The properties of the deep layers of the material do not affect the operation of the antenna at all. Antennas, elements of which are made from a solid bar, from tubes or even from thin foil glued to wooden blocks, work exactly the same with the same outer dimensions. When checking these messages, it turns out that the designer of such an antenna received a signal from a nearby repeater, which broadcast the transmission of a distant television center, or there was

accidental ultra-long-range reception due to the favorable conditions of signal propagation. When such an antenna was tested for the reception of a well-known television transmitter, naturally, no miracles were found.

Attempts have also been made to achieve a sharp reduction in the size of the antenna compared to the wavelength of the received channel. One article suggested placing the receiving antenna in a plexiglass box filled with distilled water. Assuming that water has a dielectric constant of 80, the wavelength in water should be 9 times shorter than in air. Therefore, the dimensions of such an antenna should also be 9 times smaller than in air. However, it was overlooked that for the actual manifestation of such an effect, the antenna must be in a free and uniform environment, and for this the dimensions of the vessel with water must be at least several times larger than the wavelength. Then, indeed, a small-sized antenna can be placed in the vessel.

The periodicals sometimes cite a wide variety of antenna designs for an unconventional device using various cylindrical or conical springs, as well as other exotic elements. Television reception with such antennas is, of course, possible, just as it is possible with any piece of ordinary wire. But one should not expect any improved characteristics of such antennas or any effect from their use. The time and money spent on the manufacture and installation of such antennas is always in vain.

Often, some radio amateurs or lovers of long-range television programs ask whether it is possible to install television antennas of unconventional design, whether their installation contradicts applicable laws and provisions. In our country, as well as throughout the world, there are no prohibitions on the design of receiving antennas. Any antenna design can be installed, if rooftop individual antennas are allowed at all. The fact is that on the roofs of buildings equipped with collective television antennas, the installation of individual antennas is prohibited, based on architectural and aesthetic considerations. In some cases, at the request of the local radio club, the district architect may authorize the installation of an individual antenna necessary for work for registered radio amateurs.

Separately, radio amateurs should be warned against building television antennas using mercury. The point is that working with open mercury is extremely dangerous. Mercury easily evaporates in air at room temperature, even through a significant layer of water. Mercury vapors are highly toxic and inhalation even at low concentrations leads to dangerous poisoning. Storage of mercury is allowed only in hermetically sealed metal vessels. It is strictly forbidden to use glass containers, as they break easily. Spilled mercury must be carefully collected without touching it with your hands, as it is absorbed into the skin. It is especially necessary to protect children from contact with mercury, as they can touch it with their hands and even take it in their mouths.

5.4. SYNPHASE ANTENNA ARRAYS

5. 4. SYNPHASE ANTENNA ARRAYS

An in-phase antenna array is a complex directional antenna system consisting of separate weakly directional antennas, spaced apart and located in such a way that the phases of the signals induced in them are the same. The antennas in the array are interconnected; they must work for a common matched load. As a rule, an in-phase array is assembled from identical antennas located in several rows and several floors. The connection diagram of the array antennas should be designed so that the inphase of the signals coming from each antenna to the load is not disturbed, since they will add up only with the same phases of these signals. In addition, the connection diagram of the array antennas should simultaneously ensure their matching with the load, since if the total input impedance of the array is mismatched with the load resistance, part of the energy of the signal received by the antennas will be reflected from the load and will be radiated back into space, which will lead to a decrease in the antenna array gain.

The use of several of the same antennas, connected in an in-phase array, instead of one antenna, leads to an increase in the signal at the output of such an antenna system, a narrowing of the radiation pattern and, as a result, to an increase in the gain compared to the gain of a single antenna included in the array. The increase in the gain of the in-phase antenna array is due to two factors.

First, in each antenna of the array, a signal of a certain power is induced by the electromagnetic field of the received transmitter, the same power that would be induced in a single antenna of this type and then the signal powers received by all antennas are added to the load. Therefore, the resulting signal power at the output of the in-phase array is as many times more power the signal at the output of a single antenna of the same type as the number of antennas contained in the array. Due to the fact that the load resistance remains unchanged, regardless of whether one antenna or several are used, the voltage of the resulting signal at the output of the common-mode array does not increase in comparison with the signal voltage at the output of a single antenna of the same type as many times as the antennas are contained in the array, but into a number equal to the square root of the number of antennas. So, if there are four antennas in the array, the signal power at the array output increases 4 times, and the voltage - 2 times (by 6 dB), with nine antennas, the power increases 9 times, and the signal voltage - 3 times (by 9, 5 dB), etc. Accordingly, the gain of the common-mode array increases as compared to the gain of a single antenna.

Secondly, the transverse dimensions of the antenna array relative to the direction from which the signal arrives are larger than the transverse dimensions of a single antenna. In other words, when using an in-phase array, the absorption surface of the antenna increases, the surface from which the antenna absorbs the power of the electromagnetic field. This leads to a narrowing of the radiation pattern of the antenna system, which is equivalent to

an additional increase in the antenna gain, i.e., an additional increase in the signal voltage at the output of the array. The narrowing of the radiation pattern of the array is due to the fact that only those signals that each antenna receives from the main direction perpendicular to the plane lattices turn out to be in phase. The signals arriving at an angle to the main direction arrive at the array antennas, spaced apart, not simultaneously, but with a shift in time or phase. Thus, signals arriving at an angle, due to the path difference, induce phase-shifted voltages in the array antennas, which are added geometrically like vectors. Their geometric sum turns out to be less than the arithmetic sum of the voltages induced in the array antennas by signals coming from the main direction. The larger the transverse dimensions of the grating, the greater the path difference of the signals arriving at the same angle to the main direction, and the greater the phase shift, i.e., the smaller the resulting signal. Consequently, as the absorption surface increases, the radiation pattern narrows and the in-phase array gain increases. Increasing the vertical size of the grating narrows the radiation pattern in the vertical plane, increasing the horizontal size of the grating narrows the radiation pattern in the horizontal plane. In theory, doubling the absorption surface should result in a 3 dB increase in the grating gain.

Thus, the gain of the common-mode antenna array can be determined. First of all, it depends on the gain of the antennas included in the array, and must be increased by increasing the number of array antennas, as well as by increasing the absorption surface of the array compared to the absorption surface of a single antenna.

A mistake is often made when the number of antennas included in the array is not taken into account, but proceeds only from the gain of a single antenna and the increase in the absorption surface. The origins of this error lie in the analogy between receiving and transmitting antennas, based on the principle of reciprocity. When considering a transmitting antenna, it is assumed that the transmitter power is constant and does not depend on the number of antennas in the array. As the number of antennas increases, the power available to each antenna decreases. Accordingly, the fraction of the energy of the electromagnetic field, which is due to the radiation of each of the antennas of the array, also decreases. Therefore, the field strength at the receiving point is independent of the number of antennas in the transmitting antenna array. If a separate transmitter were connected to each antenna of the transmitting array, an increase in the number of antennas in the array would lead to an increase in the radiated energy. In this case, the field strength at the receiving point would increase from an increase not only in the effective surface of the array (equivalent to the absorption surface of the receiving antenna), but also in the number of antennas in the array. It is under these conditions that the analogy between the transmitting and receiving antennas is applicable, since the field strength at the receiving point is considered inexhaustible and does not decrease with an increase in the number of antennas in the array of the receiving antenna system.

Based on the above considerations, we can conclude: for

an increase in the number of antennas of the in-phase array by 2 times and the same increase in the absorption surface, the gain of the array should increase by 6 dB. In practice, however, such an increase in the gain compared to a single antenna is not obtained due to the fact that there is a partial overlap of the absorption surfaces of individual antennas and some mismatch in the antenna phasing circuits and in the antenna impedance matching circuits and the load is inevitable. Therefore, depending on the distance between the antennas, it can be assumed that with an increase in the number of antennas in the array by 2 times, the gain increases within 4 ... 5 dB.

The directional pattern of an in-phase antenna array is determined by the directional pattern of the antennas that make up the array and the configuration of the array itself (the number of rows, the number of floors and the distance between them). With two omnidirectional antennas placed side by side at a distance equal to half the wavelength (between the axes of the antennas), the radiation pattern in the horizontal plane looks like a figure of eight, and there is no reception from lateral directions perpendicular to the main one. As the distance between the antennas increases, the width of the main lobe of the radiation pattern decreases, but side lobes appear with maxima in the directions perpendicular to the main one. With an antenna spacing of 0.6 wavelengths, the side-lobe level is 0.31 of the main lobe level, and the half-power beamwidth decreases by a factor of 1.2 relative to the array with an antenna spacing of 2/2. When the distance between the antennas is 0.75 wavelengths, the level of the side lobes increases to 0.71 of the main level, and the width of the radiation pattern decreases 1.5 times. Finally, with the distance between the antennas, equal to length waves, the level of the side lobes reaches the level of the main lobe, but the width of the radiation pattern is reduced by 2 times in comparison with the distance between the antennas in half a wave. This example shows that it is more expedient to choose the distance between the antennas equal to the wavelength. This provides the greatest narrowing of the main lobe of the radiation pattern. There is no need to fear the presence of side lobes, since when using directional antennas as part of an array, they do not receive signals from directions perpendicular to the main one.

It is impractical to locate the antennas in the array at distances less than half the wavelength (even if the design of the antennas allows it), since this overlaps the absorption surfaces and the effect is weak. It is unacceptable to increase the distances beyond the wavelength, since in this case additional side lobes appear in the directional diagram, which are not perpendicular to the main direction.

Common-mode arrays can be assembled from a wide variety of antenna types. Typically, the array uses the same antennas, which simplifies load matching and phasing. However, the use of different antennas in the array is not excluded. In conditions of long-range reception of television broadcasts, radio amateurs mainly use in-phase arrays assembled from wave channel antennas and loop antennas. Moreover, to those

the disadvantages of multi-element "Wave channel" antennas, which were considered earlier, should be added one more. Two or more antennas of this type, even if they are made exactly according to the drawings and from the same materials, turn out to be out of tune in different ways. Therefore, the phases of the signals received by them at the outputs of the antennas are not the same and the presence of skew is inevitable, which significantly reduces the gain of the array. Thus, for radio amateurs, it can be considered acceptable to use in-phase arrays assembled only from three-element "Wave Channel" antennas, the natural detuning of which, as noted earlier, is insignificant and does not lead to the need individual customization of each antenna, as well as the phasing of the antennas in the array.

As an example, Fig. 5. 1 shows a two-row antenna array assembled from two three-element "Wave channel" antennas. Antenna

Rice. 5. 1. Dual-row common-mode antenna

designed to receive a signal from vertical polarization on the border of line-of-sight and penumbra. The antenna gain is approximately 10 dB. The antenna elements are made of a metal tube with a diameter of 12 ... 20 mm for antennas operating on channels 1-5, or 8 ... 15 mm for antennas operating on channels 6-12. The arrows can be metal or wooden, the mast must be made of insulating material and only 2 m below the antenna the mast can be metal. The dimensions of each antenna can be taken from table. 4. 3, and the distance between the antennas H and the length of the loop W are given in Table. 5.1.

Table 5.1 Dimensions of two-row three-element antenna

The matching device consists of two connecting lines and a balun short-circuited quarter-wave loop. The input impedance of each antenna, given in table. 4. 3 sizes is approximately 150 ohms. The lines, each of which is made of two pieces of 75-ohm coaxial cable, also have a characteristic impedance of 150 ohms and match well with the antennas. The length of the lines can be taken arbitrary, but both lines must be the same length. At the junction points of the lines, two 150 Ohm resistors are connected in parallel to form 75 Ohms. A feeder is connected to these points using a balun. The loop and the feeder are also made of 75-ohm cable.

The in-phase of the antennas in the array is achieved by using the same antennas, the same lines, and also due to their in-phase connection. For this, points "a" of both lines must be connected exactly to points "a" (upper ends) of the vibrators of both antennas. If this antenna array is rotated 90 ° so that the antenna elements occupy horizontal position, you get a double-deck antenna array, which can be used to receive transmissions with horizontal signal polarization.

The use of in-phase antenna arrays allows, if necessary, to significantly increase the antenna protective action to attenuate interference coming from the side, opposite direction to the transmitter. To do this, in the in-phase array, you need to extend one of the antennas, for example, the lower one, as shown in Fig. 5. 2, forward towards the telecentre by a quarter of the wavelength of the received channel, while also increasing the corresponding line by a quarter of the wavelength in the cable, in this case, connected to the lower antenna. The signal coming from the front will go to the bottom

antenna 1/4 cycle earlier than the signal arriving at the upper antenna. But due to the longer line, the signal from the lower antenna will also be delayed by 1/4 of the period. Thus, the signals from the lower and upper antennas to the connection points of the lines will arrive simultaneously, in phase, and will be added. Noise coming from behind will arrive at the lower antenna with a 1/4 cycle delay compared to the noise arriving at the upper antenna. Additionally, the interference received by the lower antenna will be delayed by the longer connecting line for an additional 1/4 period. Thus, the interference received by the lower antenna will arrive at the connection point half a period later than the interference received by the upper antenna. Therefore, they will be in antiphase and will be subtracted. This method makes it possible to increase the SPL of the antenna array by about 20 dB if the directions to the signal and interference sources are opposite, i.e., the angle between these directions is 180 °. However, even at smaller angles, up to 150 °, it makes sense to use this method of increasing the QED.

This may be necessary when a weak signal from a distant television transmitter cannot be received with satisfactory quality due to the presence of a closer or more powerful transmitter operating on the same channel. When building an antenna array with an increased CPV, it must be remembered that the wavelength in the cable is 1.52 times less than the wavelength in free space... Therefore, you need to push one of the antennas forward by 1/4 of the wavelength in free space (this size corresponds to the W dimension in tables 4.6 and 5.1), and you need to lengthen one of the connecting lines by 1/4 of the wavelength in the cable (this the size corresponds to the size T in table 4. 6). The difference in the W dimensions given in these tables is explained by the fact that the dimensions of one of the tables are calculated for tuning the antenna to the carrier frequency of the image, and the other to the center frequency of the channel.

In fig. 5. 3 shows a four-story in-phase array, assembled from four three-element "Wave channel" antennas. Placing antennas in four levels significantly narrows the vertical radiation pattern and allows you to press its lobe to the ground. This is very important in conditions of long-range television reception, when the signal comes from the horizon line. The gain of such an antenna array reaches 14 dB. The dimensions of the antennas can be taken from table. 4. 3. Antenna matching is carried out as follows. The first (lower) floor is connected to a second 150 ohm connecting line formed by two pieces of 75 ohm coaxial cable. The length of the connecting lines that connect the first to the second and the third to the fourth floors should be equal to half the wavelength in the cable. Due to the fact that the signal

passing along lines of this length, it is delayed for half a period, that is, its phase is reversed, to compensate, the cable sections in the lines are crossed. At the power points of the antennas of the second and third floors, two 150 Ohm resistances are connected in parallel, forming 75 Ohms. Transformers are connected to these points, formed by sections of a 50-ohm cable with a characteristic impedance of 100 ohms of length T. Therefore, at points "in-to", the input impedances of the two lower floors and the input impedances of the two upper floors are equal to 150 ohms, connected in parallel, forming 75 ohms ... The feeder is connected to these points using a quarter-wave balun of length W. The dimensions of the transformers T and the loop W can be taken from one of the tables placed earlier. At the ends of the lines and transformers, the cable sheaths are interconnected. The central core of the feeder, connected to the central core and the braid of the loop, is connected to the left point "b", and the braid of the feeder is connected to the right point "b". The braid of the feeder is not connected to the braids of the transformers.

In § 4. 9, a seven-element broadband antenna of the ATVK-7 / 6-12 type was considered, designed to receive transmissions on any of the channels in the sixth to twelfth range. The broadband of this antenna is achieved by the mutual detuning of its elements and, as a result, the gain is small. Some radio amateurs are trying to collect common-mode arrays from such antennas to increase the gain and use such arrays in long-range reception conditions. All attempts lead to negative results on following reasons... The ATVK-7 / 6-12 antenna is designed for use in a relatively close proximity to a television transmitter, therefore it is not matched with the feeder, but is only symmetrical using a cable loop. It is impossible to match the antennas in the array in terms of their input impedance with the characteristic impedance of the feeder in the entire range, since the matching is carried out by resonant elements - resistance transformers, made from cable lengths of 1/4 wavelength. Such an element is a transformer only at the signal frequency at which its length is equal to 1/4 of the wavelength. At a different frequency, the length will already differ from 1/4 of the wavelength and as a transformer it will no longer work, therefore, a mismatch will occur. Besides, antennas of this type are not identical in their phase characteristics. The phases of the signals at the outputs of two externally identical antennas can also be unequal. This also applies if the antennas are used to assemble an array designed to operate on only one channel. In this case, it is impractical to use broadband antennas. It is more profitable to use in the array either simpler antennas with the same gain, but a stable phase characteristic, or antennas of the same degree of complexity, but narrow-band, with a higher gain. The same considerations can be applied to other types of broadband antennas. Collecting in-phase arrays from them is sometimes impractical because of the difficulties in matching, sometimes because of the difficulties in phasing.

Nice results give in-phase arrays assembled from loop antennas. In the meter wave ranges, the most widespread are two-story and two-story double-row in-phase arrays assembled from two-element loop antennas. In fig. 5.4 shows a two-level in-phase array and a circuit of a balun-matching device to it. Both antennas of this array are made according to Fig. 4. 5 and tab. 4. 5. Balancing of the antennas is carried out by quarter-wave balun short-circuited loops, which do not change the input impedance of the antennas. Therefore, the lines, made like stubs from a 75-ohm cable, match well with the antennas. Lines are taken of arbitrary, but the same length. At the junction of the lines, two 75 Ohm resistors are connected in parallel to form 37.5 Ohms. For

Rice. 5. 4. Double-deck common-mode loop antenna

matching this resistance with the characteristic impedance of the feeder, which is 75 Ohm, a transformer is used in the form of a piece of cable 1/4 of the length of the water in the cable. The characteristic impedance of the cable from which the transformer is made is determined by taking the square root of the product of the resistances at the input and output of the transformer, which gives 53 ohms. Thus, the transformer must be made of a cable with a characteristic impedance of 50 ohms.

Difficulties often arise due to the lack of a piece of 50-ohm cable. In this case, matching can be performed according to another scheme shown in Fig. 5. 5. All elements of this circuit are made with a cable with a characteristic impedance of 75 Ohm. The circuit uses two transformers connected in series. The first transformer is formed by three parallel cable lengths and has a characteristic impedance of 25 ohms. The second transformer is formed by two cable sections and has a wave

resistance 37.5 Ohm. The input resistance of the grating is 37.5 ohms, at the output of the first transformer it decreases to 16.7 ohms, and at the output of the second transformer it increases to 84.4 ohms. Although there is no full matching of such resistance with the characteristic impedance of the feeder equal to 75 Ohm, the mismatch can be considered quite acceptable. With this mismatch, the traveling wave ratio is 0.89, which corresponds to the transmission to the feeder of 98% of the signal power received by the antenna. The gain of a two-story in-phase array of two two-element loop antennas is approximately 12 ... 13 dB.

If it is necessary to increase the CPL of a two-story loop antenna, the upper antenna moves forward towards the TV center by a distance equal to Ш, and the upper line is lengthened relative to the lower one by a length T.

A two-story array of loop antennas has a narrow vertical directional pattern and a wider horizontal one. This is very convenient, since the antenna array does not need to be carefully oriented in azimuth, and the narrow lobe of the directional pattern in the vertical plane, pressed against the horizon line, favors long-range television reception. It is recommended to use this antenna array in the penumbra zone adjacent to the line of sight.

If, after installing a two-story in-phase array of loop antennas, it is experimentally established that its gain is insufficient to obtain reliable reception with good quality image, you can make two more loop antennas and assemble an array of four antennas located in two rows and two floors. Such an antenna array with a matching circuit is shown in Fig. 5. 6. All of her

Rice. 5. 6. Double-deck double-row loop antenna

the dimensions are taken from table 4. 5. Due to the doubling of the rows, the directional pattern of the array in the horizontal plane is narrowed, and the gain increases to 16 ... 17 dB. It is advisable to use such an antenna array in the far part of the penumbra zone.

All elements of the balun-matching device are made of 75-ohm cable sections. The input impedance of the two upper antennas at the junction of the upper lines is 37.5 ohms. The top transformer boosts it to 150 ohms. The two lower antennas have the same input impedance. At the junction of the transformers, two 150 ohm resistors are connected in parallel to form 75 ohms. This is where the feeder is connected. The agreement is good enough. In-phase is ensured by the same antennas and the same length of all four lines, which can be chosen arbitrarily. To maintain in-phase, you need to turn Special attention on the correct connection of the lines to the antennas: the central cores of all four lines are connected to the left ends of the vibrator frames, and the braids to the right. Otherwise, skewing will occur.

If it is necessary to increase the CPV, the two upper antennas are pushed forward by a distance of Ш, and both upper lines are lengthened relative to the lower ones by the length T.

In this design of the antenna array, the crossbeams must be made of insulating material. You can use textolite, vinyl plastic or wooden slats, boiled in some kind of anti-rotting composition and painted. The mast can be made of metal. To avoid bending of the beams, the mast can be made protruding upward beyond the antenna to a height of Н / 2 and all antenna booms can be tied to the top of the mast with a nylon cord (wire cannot be used!). At the top of the mast, you can install a lightning rod in the form of a pointed metal rod, welded to the mast, if it is metal, or connected by a thick wire running along a wooden mast, with a reliable ground at the base of the mast. The metal mast is also reliably grounded.

In-phase arrays assembled from three-piece loop antennas are very attractive. A two-level in-phase array assembled from two three-element loop antennas should have a gain of about 19 dB, and a two-level two-row in-phase array of four three-element loop antennas should have about 23 dB, which corresponds to an increase in the signal voltage at the output of the antenna array 14 times compared to half-wave vibrator. The dimensions of the three-element loop antennas can be taken for the decimeter range from Table. 3.2, and for the meter range - from table. 4. 6. The coordination is carried out in accordance with fig. 5.4 or 5.5 for a two-storey array of two antennas, or fig. 5. 6 - for a two-storey two-row array of four antennas. According to the same figures, the design of the antenna arrays themselves is performed.

Despite the fact that the design of a two-story double-row array, assembled from three-element loop antennas, for meter bands turns out to be quite cumbersome (especially for channels 1 and 2), it can be recommended for reliable reception of transmissions at the far border

penumbra or in cases where using simpler antennas does not give good results.

When manufacturing three-element loop antennas for the decimeter range, the distance between the ends of the vibrator frame, as shown in Fig. 3. 6 is taken equal to 15 mm. Such a small distance was taken so that it was significantly less than the side of the square of the frame. If the antenna is designed to operate in the meter range, this distance can be increased to 40 mm.

Table 4. 6 the distance between the three-element loop antennas of the in-phase array vertically and horizontally H is indicated as the maximum allowable, approximately equal to the wavelength to obtain the highest gain. If such large distances prove to be unacceptable due to the bulkiness of the structure, the horizontal spacing of the antennas can be reduced by 1.5 times, although the gain of the array will decrease by about 1 dB. It is also possible to reduce the distance between the floors of the grating also by 1.5 times, if necessary, which will lead to a decrease in the gain of the grating by another 1 dB. In general, it is not at all necessary that the distances between the floors and the rows of the lattice be equal to each other.

A two-story double-row in-phase array is rather cumbersome, especially for receiving transmissions on 1-5 channels. In conditions of long-range reception

Rice. 5. 7. Three-deck loop antenna

television in the penumbra zone, when the transmitting antenna is behind the horizon, it is especially important that the main lobe of the receiving antenna is pressed to the Earth. At the same time, due to the low field strength, orientation of the antenna in azimuth with a narrow radiation pattern in the horizontal plane presents certain difficulties. Therefore, we can recommend a three-story single-row in-phase array of three two-element or three-element loop antennas shown with the matching circuit in Fig. 5. 7. All dimensions here are the same as for the already considered loop antennas and in-phase arrays of them The peculiarity is that to match this array from the feeders, two transformers connected in series are required. Transformer 1 is formed by parallel connection of pieces of 75-ohm and 50-ohm cables, transformer 2 is made of a piece of 50-ohm cable. Recall all three lines are made of the same length from the same brand of 75 ohm cable.

The gain of such an array of two-element loop antennas is 14-16 dB, which corresponds to an increase in the signal voltage by 5- (times, and from three-element loop antennas about 21 dB, which corresponds to an increase in the signal voltage by 11 times relative to a half-wave vibrator. directivity is relatively wide.

Rice. 5.1. Dual Row Common Mode Antenna

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Rice. 5.2. In-phase array with increased KZD

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Rice. 5.2. Four-story common-mode lattice

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Rice. 5.4. Double Deck Common Mode Loop Antenna

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Rice. 5.5. Dual Deck Antenna Matching Option

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Rice. 5.6. Double Deck Dual Row Loop Antenna

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Rice. 5.7. Three-deck loop antenna

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Table 5.1 Dimensions of two-row three-element antenna

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5.5. DIRECTIONAL DIAGRAMS OF SYNPHASE GRIDS

5. 5. DIRECTIONAL DIAGRAMS OF SYNPHASE GRIDS

The radiation pattern of an in-phase antenna array is determined by the radiation pattern of the antennas themselves included in the array, and, in addition, by the parameters of the array. If the lattice is formed in vertical direction, that is, built in two or more floors, the radiation pattern in the vertical plane is narrowed. If the grating is formed in the horizontal direction, the radiation pattern is narrowed in the horizontal plane. Finally, great importance has a spacing between antennas in an array.

Let us consider the formation of the directional diagram of a grating consisting of two half-wave vibrators located side by side, at a distance H between them (Fig. 5. 8). If the signal comes from a direction perpendicular to the plane in which the antennas lie, the phases of the EMF induced in the antennas are the same and the powers of the received signals are added arithmetically. If the signal arrives at an angle i different from 90 °, as shown in the figure, the signal to antenna 2 arrives later than to antenna 1 due to the fact that the path difference d = Hcosa appears. The delay of the signal arriving at antenna 2 leads to a phase shift of the EMF induced in antenna 2 with respect to the EMF induced in antenna 1. This phase shift angle (c) refers to the total angle 2 * 3.14 as the path difference d refers to wavelength:

In fig. 5.10 shows the directional diagram of the specified in-phase array in one horizontal half-plane (the diagram in the second half-plane is similar) for five different meanings K. It can be seen that with a spacing between the antennas equal to half the wavelength (K = 0.5), the diagram has one lobe with a width at the 0.7 level (half power level) slightly less than 50 °. For comparison, it can be indicated that the width of the radiation pattern of a single half-wave vibrator at the same level is slightly more than 100 °. This means a significant increase in the gain of the antenna array compared to a single antenna. The spatial selectivity of the antenna is also improved. When the interference arrives at an angle of a = 45 °, the induced EMF in the array is 0.28 from the maximum, and in a single half-wave vibrator is 0.63. Thus, the interference is weakened in voltage by a factor of 2.25, and in power - by a factor of 5, that is, by 7 dB.

The diagram shows that side lobes appear when the antenna spacing is greater than half the wavelength. If the spacing is 0.75 wavelengths, the plot contains two sidelobes at 0.75 from the maximum. With a further increase in the spacing, the level of side lobes also grows, reaching 0.7 at K = 1.5. If the spacing exceeds 1.5 wavelengths, the diagram acquires four side lobes instead of two. So, at K = 2, two petals have a level of 0.29 (a = 27 °) and the other two - 0.83 (a = 61 °). High-level side lobes are extremely harmful, since they greatly impair the spatial selectivity of the antenna not only to industrial noise, but also to reflected signals, which can lead to repeats on the TV screen. True, in this case, the main petal turns out to be very

Rice. 5.10 Co-phase array radiation patterns

narrow: its width at the level of 0.7 does not exceed 15 °. However, the intense sidelobes negate this advantage. Therefore, it is recommended to choose the spacing between the antennas in the range from 0.5 to 0.75 of the full received channel length. As a last resort, if you need a particularly high grating gain, you can increase the spacing to wavelength, which will narrow the main lobe to 28 °. It is useful to remind: the narrower the directional pattern of the antenna, the greater its gain. It is not recommended to increase the spacing between antennas beyond the value equal to the wavelength.

The given radiation patterns were calculated for an in-phase array, assembled from two half-wave dipoles, as the simplest antenna, for which the analytical expression of the pattern is also the simplest. However, the basic properties of radiation patterns remain the same for in-phase arrays of more complex narrow-band antennas designed to receive one specific frequency channel. If a narrow-band antenna is capable of receiving several channels adjacent in frequency, as, for example, in the decimeter wavelength range, it is necessary to provide that for itself high frequency channel the spacing between the antennas did not exceed the wavelength.

It is quite characteristic that in all the given radiation patterns, regardless of the spacing between the antennas (for any value of K), there is no reception from the lateral directions (a = 0). This is explained by

theoretically, half-wave vibrators (like most other television antennas) have no lateral reception. However, in practice, due to the fact that it is impossible to make an absolutely precise antenna, poor reception side can take place. And, if in the lateral direction a powerful television transmitter is located close, operating on the same or on an adjacent frequency channel, it can create a noticeable interference with the reception of the main signal. Such interference can be expressed in synchronization failures or in the overlay of a faint extraneous picture on the main image, moving in the horizontal or vertical direction. For a sharp attenuation of such interference, it is advisable to use, instead of one antenna, an in-phase array of two of the same antennas located side by side at a distance equal to half the wavelength of the frequency channel on which the interfering transmitter operates. Due to the fact that the interference arrives at the array antennas not simultaneously, but with a time shift of half a period, their phases are shifted by 180 °. If the antennas are exactly the same, such a shift leads, when added, to cancel the interference received by the antennas. Lines of the same length from a 75-ohm coaxial cable are connected to both antennas using balun-matching devices designed for this type of antennas, and the lines are connected to the feeder using a quarter-wave transformer from a piece of 50-ohm cable, as shown in Fig. 5.4, ​​the length of which T corresponds to a quarter of the wavelength in the cable for the main channel. In addition to weakening interference, such an array will provide an increase in the level of the useful signal by about 3 dB by increasing the gain and will weaken the reception of reflected signals due to the narrowing of the antenna array radiation pattern in comparison with the width of the pattern of one previously used antenna.

The creation of such a two-row in-phase array with a row spacing equal to half the wavelength can be difficult when using wave-channel antennas. The fact is that the reflector length of these antennas exceeds half the wavelength, and the required spacing between the antennas is not feasible. Therefore, such an array can only be assembled from antennas, the maximum horizontal size of which is less than half the wavelength. As an example, Fig. 5. 11 shows an in-phase two-row array of two-element loop antennas. All dimensions of this array can be taken from table 4. 5. The same array can be assembled from three-element loop antennas with dimensions according to table 4. 6 for the meter range or table 3.2 for the decimeter range. However, for a decimeter array, the distance between the antennas is taken equal to half the wavelength of the image channel (Table 1.2) of the interfering television transmitter.

In-phase lattices containing two or more floors are widely used. Therefore, it is important to know how the spacing between floors affects the shape of the radiation pattern in the vertical plane. For long-range reception on flat terrain, it is necessary for the antenna to receive the signal best from the horizon - at an elevation angle of zero. Regardless of the number of grid floors and the spacing between floors, at zero elevation, the radiation pattern has a maximum. However, in hilly or mountainous terrain, as well as in ultra-long-range reception

Rice. 5.11 Double-row phased array

(when using reflection from the ionosphere) the signal can arrive at other elevation angles. If (as for the directional pattern in the horizontal plane) to analyze the shape of the diagram of a two-storey array of two half-wave vibrators, under these conditions, the optimal spacing between the floors is equal to half the wavelength of the received frequency channel. The radiation pattern of such a two-story array contains one lobe with zero reception from the zenith (90 ° elevation), and the half power level corresponds to an elevation of 30 °. A sufficiently wide radiation pattern in this case favors the reception of a signal from directions at angles relative to the horizon line. When it is required to provide long-range reception by increasing the antenna array gain, it makes sense to increase the spacing between floors. At 3/4 wavelength spacing, a side lobe appears at 90 ° elevation and the main lobe tapers to a half power elevation angle of about 20 °, and zero reception corresponds to an elevation angle of 42 °. An even narrower main lobe can be obtained with a wavelength separation between floors. In this case, a side lobe directed to the zenith is also formed, the elevation angle corresponding to half the power is 14.5 °, and zero reception

30 °. Finally, it is acceptable to increase the separation to one and a half wavelengths. In this case, the side lobe has a maximum at an elevation angle of about 42 °, half the power of the main lobe corresponds to an elevation angle of 9.6 °, and zero reception

20 °. Do not increase the spacing beyond this value, as two side lobes appear. So, with a spacing between floors of 2.5 wavelengths, the main lobe directed to the horizon line (the elevation angle is zero) turns out to be very narrow: half the power of the main lobe of the diagram corresponds to an elevation angle equal to only 5.7 °, but the directional diagram of the grating is In this case, it turns out to be indented with side petals. The lateral lobe closest to the main has a maximum elevation angle of 23.6 ° and is separated

from the main petal by the direction of the bullet reception at an elevation angle of 11, 5 °. The second side petal has a maximum at an elevation angle of 53 ° and is separated from the first side petal by the second direction of the bullet reception at an elevation angle of 37 °. If there are even small hills on the path, you cannot deny the possibility of a signal arriving at a small elevation angle, which will fall into the area of ​​the radiation pattern corresponding to a bullet reception. In this case, the signal cannot be received or will be significantly weakened.

Although the above analysis of vertical patterns was for a two-deck antenna array of two half-wave dipoles, the same pattern should be for arrays assembled from more complex antennas, for example, from antennas of the "Wave" type or from loop antennas. The difference will be only in the values ​​of the elevation angles corresponding to half power, zero reception and side lobe maxima. Therefore, when choosing the size of the spacing between the floors of an in-phase array assembled from a variety of (but the same!) Antennas, one can be guided by the above considerations.

Rice. 5.10 Common-mode array radiation patterns

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Rice. 5.11 Double-row phased array

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Rice. 5.8. To determine the travel difference

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Rice. 5.9. Vector addition

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5.6. ELECTRIC SCANNING OF TELEVISION ANTENNAS

5. 6. ELECTRIC SCANNING OF TELEVISION ANTENNAS

Antenna scanning is called a controlled spatial movement according to a certain law of the direction of maximum reception, in which a given sector or other area of ​​view is sequentially "scanned". So, the antenna of a radar station with a circular view rotates around the vertical axis and for each revolution it allows you to survey the entire surrounding space. Such scanning is mechanical - mechanical rotation of the antenna provides an overview of a given area. In contrast to mechanical scanning, in recent years, electrical scanning is often used in radar, in which the antenna is a fixed array, and the change in the direction of the main lobe of the radiation pattern is achieved by appropriate phasing of the array antennas. If, for example, the signals received by two antennas are added directly, the maximum of the main lobe of the pattern is perpendicular to the line connecting the antennas. But if, before adding the signals, one of them is delayed for a part of the period, that is, it is shifted in phase relative to the signal received by the other antenna, the radiation pattern will rotate by a certain angle, for which the path difference will be compensated by the introduced delay. With the main and continuously changing phase shift, the maximum of the directional diagram also smoothly and continuously changes its direction.

In the technique of television reception, the semblance of mechanical scanning has been used for a long time. In this case, the antenna was installed on a rotary mast and either manually or using an electric motor equipped with a gearbox, it was turned in the direction of the desired television transmitter. Such devices were used by amateurs of television reception quite rarely, as they were bulky and expensive.

The principle of electrical scanning makes it very easy to rotate the maximum of the radiation pattern of a fixed antenna array for

by phasing its antennas. Let's go back to fig. 5. 8. Let antennas 1 and 2 be omnidirectional. If the direction to the transmitter is perpendicular to the line connecting the antennas, the signals they receive will be in phase, and the maximum of the pattern will be directed to the transmitter. If the transmitter is at an angle a, between the received signals there is a phase shift in , corresponding to the path difference, and reception will occur on the slope of the radiation pattern. But it is enough to delay the signal received by antenna 1 by shifting it in phase by the same angle in so that both signals are in phase. As a result, the maximum of the diagram rotates and turns out to be in the direction a. When using directional antennas, the dependence of the angle of maximum reception on the phase shift of one of the signals becomes complex. The directional pattern of a phased two-row array of half-wave vibrators with a distance between them equal to half the wavelength is described by the formula:

In this formula, the angle в corresponds to the required delay of the signal received by antenna 1 in order for the maximum of the array radiation pattern to be turned in the direction a.

The radiation patterns of the considered array for five values ​​of antenna phasing are shown in Fig. 5. 12. When considering diagrams

the following conclusions can be drawn. The phasing of the grating leads to the bifurcation of the diagram into two lobes. With an increase in the phasing angle, the main lobe decreases, and the side lobe increases. When the phasing angle reaches 180 °, the petals become the same !. The calculation shows that with a further increase in the phasing angle, the side lobe becomes the main one, which is equivalent to the phasing of another antenna. Due to the fact that the half-wave vibrator receives signals in the same way from the front and from the back, the directional pattern in the opposite half-plane is similar to that shown.

The absence of an analytical expression for the radiation patterns of other antennas does not make it possible to trace the results of their application in a phased array, but we can assume that they will be qualitatively the same.

For example, we can recommend the use of a phased array when it is necessary to receive programs from two television transmitters operating on the same or adjacent channels in frequency and located in different directions.

The phasing of the antenna in the array is easy to carry out due to the different lengths of the lines, for example, shown in Fig. 5. 11. The increase in the length of one line relative to the other is made by the value z, which depends on the required phasing angle in (in degrees) and the signal wavelength L, in the cable (in mm) according to the following formula (the wavelength in the cable is 1 , 52 times less than in free space).

Rice. 5.12. Radiation patterns of the considered array

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Increasing the length of one line relative to the other

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Radiation pattern of a phased two-row array

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5.7. PASSIVE RELAYERS

5.7. PASSIVE RELAYERS

There are such conditions when confident reception of television broadcasts is impossible due to excessive low level field strength at the receiving point. This may be due to the long distance to the television transmitter, but sometimes the reason is that the terrain is unfavorable and the receiving point is located in a hollow. In this case, the presence of a hill or mountain obstacle prevents the direct passage of the signal. In such conditions, they resort to using an active or passive repeater.

An active repeater is a collection of a receiving antenna, a complete radio receiver television signal, a frequency spectrum converter, a converted signal radio transmitter and a transmitting antenna. A frequency spectrum converter is necessary in order for the signal transmission by the repeater to be carried out on a different frequency channel relative to the channel through which the signal was received. This is required to eliminate interference for those TVs that may fall into the area where reception of both the main signal and the relayed signal is possible. In the early years of development mass television When the number of television centers was small, some radio amateur groups created active repeaters to ensure the possibility of reliable reception of television broadcasts in their village. Currently, the network of operating

television centers and state-owned active repeaters has become so dense that it is sometimes impossible to choose a free channel number that does not interfere with the signals of surrounding transmitters. Therefore, the authorities of the Ministry of Communications strictly prohibited the construction of amateur active repeaters. The installation of state active repeaters is carried out according to the plan, taking into account the already operating transmitters in each region and their frequency bands. At the same time, in order to install a new repeater, it is often necessary to change the channel numbers of the existing television centers and repeaters.

The passive repeater differs in that it does not contain transceiving or amplifying equipment, and reception and transmission are carried out exclusively by antenna systems.

There are three types of passive repeaters: refractive, reflective and obstacle.

A refractive repeater in the simplest case is a combination of two highly directional antennas, one of which is oriented towards the transmitter antenna, and the other is directed to the receiving point. Thus, the signal is re-emitted in the desired direction.

The repeater of the reflecting type is made in the form of one or two flat antenna mirrors, which provide a change in the direction of signal propagation. Refractive and reflective repeater antennas must be made with high precision working surfaces at large sizes canvases of these antennas, reaching hundreds of square meters in the television frequency range. In addition, a rigid fixation of the working surfaces of the antennas in space must be ensured, which requires the use of super-rigid supports. Therefore, repeaters of refractive and reflective types in Lately rarely find application on state communication lines and are completely unacceptable in radio amateur conditions for receiving television broadcasts.

The passive repeater of the obstacle type was proposed in 1954 by G. Z. Aisenberg and A. M. Model. Such a repeater is a metal surface located between the transmitter and the receiver, which is relative to the transmitter in the shadow zone (Fig. 5. 13). In the absence of a repeater, the transmitter antenna installed at point A practically does not create an electromagnetic field at the receiving point B, since the receiving point is shaded. When an obstacle is placed in the path of signal propagation at point C, a field appears at point B. This is due to the fact that

Rice. 5. 13. To the explanation of the installation of a passive repeater

an obstacle in accordance with the Huygens principle is excited by a wave incident on it and becomes a source of secondary radiation. With an appropriate choice of the shape and size of the obstacle, the field strength at point B may be significant and sufficient for reliable reception of a television signal. The role of the obstacle is that a surface with zero field strength is formed on the signal propagation path on the side facing the receiving point.

Deformations of the working surface of the repeater, such as obstacles, caused by the wind, or its deviations due to inaccuracy of manufacturing, do not affect the radiation intensity and the level of field strength at the receiving point. This is the main advantage of obstacle type repeaters over refractive and reflective type repeaters. Therefore, the web of the repeater of the type of obstacle can be made not in the form of a rigid metal structure, but in the form of a wire mesh, the rigidity of the frame structure of such a mesh is determined exclusively by the necessary mechanical strength. There is also no need to align the working surface of the repeater after its installation, which is mandatory for repeaters of refractive and reflective types. All this indicates that passive obstacle type repeaters can be widely used for reliable reception of television broadcasts in difficult terrain conditions when installed by radio amateurs.

The optimal shape of the obstacle-type repeater web is arched. However, in practice, due to the fact that the horizontal dimensions of the canvas are much less than the distance to the relayed transmitter, the arc degenerates into a straight line, and a rectangular canvas gives the same results. The repeater web is installed in a vertical plane perpendicular to the line connecting points A and B. The installation of the repeater web on the supports is shown in Fig. 5. 14. The maximum height of the web is equal to the height of the Fresnel zone and can be determined by the formula

The greatest width of the web is determined by the permissible skewing of the fields emitted by the middle and edges of the web:

Rice. 5. 14. Cloth of the Passive repeater

In these formulas L - the wavelength of the received television channel, a - the angle between the directions of the field incident on the canvas and the radiated field to the receiving point, R2 is the inclined distance between the repeater canvas and the receiving antenna. The formulas are valid when the distance between the transmitting antenna and the repeater is much greater than the distance between the repeater and the receiving antenna. Otherwise, instead of R2, the value R1R2 / (R1 + R2) should be substituted into the formula. The dimensions of the canvas are obtained in meters, if distances are also expressed in meters.

When calculating the dimensions of a passive repeater, it should be taken into account that the dimensions obtained are the maximum permissible: an increase in these dimensions leads to a decrease in the effectiveness of the repeater. In fact, in the I and II bands of meter waves, these dimensions may be really impracticable. Let us give next example... Suppose the distance from the transmitter to the repeater is R1 = 30 km, the distance from the repeater to the receiving antenna is R2 = 1 km, and the angle between these directions is a = 10 °. Then, for the first television channel with a wavelength of L = 6 m, the maximum height of the web will be 17.3 m, and the maximum width of the web is 132 m.Under such conditions, the web can be made smaller, although the effectiveness of the repeater, which is proportional to the surface area of ​​the web, will decrease ... For the same conditions, if transmissions are received on the 12th channel with a wavelength of 1.32 m, the dimensions of the canvas are already closer to reality: height -3.7 m, width - 61.3 m. Finally, for the 33rd channel of the decimeter wavelength range at a wavelength of 0.53 m, the dimensions of the canvas are even smaller: height - 1.5 m, and width - 39.1 m.

The effectiveness of a passive obstacle-type repeater can be characterized by the ratio of the field strength at the point where the repeater is located to the field strength at the receiving point:

the field strength at the receiving point will be 5, 3; 11, 2 and 18 times less than the field strength at the point where the repeater is installed for channels 1, 12 and 33, respectively.

It can be seen from the transformed formula that at small angles a, the field strength at the receiving point is inversely proportional to this angle, and its dependence on the distance to the repeater and on the wavelength is weaker,

since their values ​​are included in the formula under the radical sign, if the dimensions of the canvas are chosen as maximum permissible. In the same time maximum dimensions canvases depend on the wavelength, with decreasing wavelength they also decrease, especially the height of the web, which depends from wavelengths to the first power. Thus, the effectiveness of the repeater with decreasing wavelength could be increased if it were possible to increase the dimensions of the web beyond the maximum allowable. This turns out to be possible if the canvas is made not continuous, but consisting of several horizontal stripes that overlap the Fresnel zones through one, i.e., one sign. Due to the fact that in decimeter wavelengths the maximum allowable height of the canvas turns out to be small, it is possible to make a canvas from two or three strips, and the height of each strip and the distance between them in height are taken equal to the found value maximum height canvases. Such repeaters are called multi-element.

The effectiveness of an obstacle-type multi-element repeater increases in proportion to the square of the number of lanes. Thus, if in the given example we make a repeater canvas for the 33rd channel of three strips with a height of 1.5 m each with a distance between them in height also 1.5 m, the efficiency of the repeater will increase 9 times. In this case, the field strength at the receiving point will no longer be 18 times less than the field strength at the point where the repeater is installed, but only two times.

On flat terrain with a long route, the use of radio amateur passive repeaters such as obstacles becomes unrealistic for the following reasons. The installation of the repeater should be carried out at such a point on the route where the field strength is high enough, and this point is usually located tens of kilometers from the receiving point. With an increase in this distance, the effectiveness of the repeater decreases when the effective surface of the web is equal. The angle between the directions of the field incident on the repeater and the field emitted to the receiving point decreases to fractions of a degree, which leads to an increase in the maximum allowable height of the web. In this case, the installation of a multi-element repeater, even for the decimeter range, becomes unrealistic due to the fact that in such conditions the height of each band and the distance between them in height are unacceptably large.

It is advisable to install passive repeaters of the obstacle type in conditions when the receiving point is closed in the direction of the transmitter by a nearby high obstacle, and at the top of this obstacle, on which the repeater will be installed, the signal field strength is quite high. Then the web of the repeater can be made to the maximum permissible size even for the first television channel, and for the 12th channel the repeater can be made multi-element.

Let us now consider the practical implementation of the repeater web. The theory of passive repeaters is based on the assumption that the obstacle is a solid sheet of metal. In practice, however, the web is made in the form of a wire mesh. Such grids reflect electromagnetic waves well if the polarization of the incident field is parallel to the wires of the grid. Then, with horizontal polarization of the signal, the web should be made in the form of horizontal wires, and with vertical

polarization - vertical. The distance between the wires should be significantly less than the operating wavelength. It can be considered sufficient if their ratio is not less than 20. The diameter of the wires also matters: the larger the diameter of the wires, the less the leaked power and the better the canvas works. Good results in the manufacture of the repeater web are obtained by the antenna cable. To ensure the strength of the wires, the canvas can be fastened with transverse wires of any diameter, piercing all the intersection points. The distance between the cross wires is chosen arbitrarily for reasons of mechanical strength. The repeater canvas is installed on two or more supports. If intermediate supports are used, all parts of the web must be in the same plane. The rectangular shape of the canvas is ensured by its suspension to a nylon cord. There is no need to isolate the canvas from the supports. The height of the lower edge of the web above the earth's surface should be at least several wavelengths of the received channel.

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5.8. FEATURES OF ULTRA LONG TELEVISION RECEPTION

5. 8. FEATURES OF ULTRA LONG TELEVISION RECEPTION

As already noted, ultra-long-range television reception is observed relatively rarely, its sessions are short and cannot be predicted. Ultra-long-range reception is possible in case of randomly formed favorable conditions for signal propagation. Let's consider what these conditions are and what explains the ultra-long-range television reception?

As you know, the basis for the propagation of radio waves in the long-wave and medium-wave ranges is the earth wave, which is characterized by the fact that the energy of the electromagnetic field bends around the earth's surface due to refraction in the atmosphere. This refraction occurs due to the decrease in air density with height. Short-wave radio waves are weakly refracted in the atmosphere, but can be reflected from the upper ionized layers of it.

For a long time it was believed that VHF radio waves do not bend around the earth's surface (are not subject to refraction) and are not reflected by the ionosphere. This, however, turned out not to be the case. The degree of ionization of the layers of the ionosphere increases sharply during the years of solar activity, as well as for other reasons. This creates conditions conducive to the reflection of VHF waves. The most important in this respect are the E layer, located at an altitude of 95 ... 120 km above the earth's surface, and the F2 layer, located at an altitude of 230 ... 400 km. It is believed that the formation of the E layer is associated with the ionization of nitrogen and oxygen molecules by the X-ray and ultraviolet radiation of the Sun, and the formation of the F2 layer is associated with the ionization of the same gases by the ultraviolet and corpuscular radiation of the Sun. The E layer is characterized by a high constancy of the electron concentration from day to day, which increases during the day and decreases at night, while the F layer is an unstable formation. In this layer, both the electron concentration and the height of the location of its maximum fluctuate within significant limits on different days. However, during the day, the concentration of electrons in this layer is also higher than at night, and, in addition, in winter it is much higher than in summer. In the predawn hours, a deep minimum of the electron density of the F2 layer is observed.

From time to time, a highly ionized layer is formed in region E, which is called "sporadic E layer". The intensity of the sporadic E layer is many times higher than the intensity of the normal E layer. Studies have shown that the sporadic E layer is an accumulation of electron clouds that have a horizontal length of tens and hundreds of kilometers and move at a speed of up to 300 km / h. The lifetime of this layer varies widely, but does not exceed several hours. The sporadic E layer can appear at any time of the day or year, but in mid-latitudes it is more often formed on summer days. It is assumed that the formation of the sporadic E layer is associated with the leakage of charged particles from the higher layers and with streams of meteors. Just as long-wave and medium-wave radio waves are refracted in the atmosphere, UV-C radio waves are refracted in the ionosphere. The degree of refraction depends on the electron concentration of the layer and on the length of the radio wave or its frequency.

The higher the frequency of the wave, the higher the concentration of electrons is required in order for the wave to return to the Earth due to refraction and total internal reflection. In addition, it has been proven that at the point of wave reflection, the electron concentration must necessarily increase with height. Reflection cannot occur in the region of the maximum, and even more so in the region of the decrease in the electron concentration with height. The inconstancy of the electron concentration in the ionized layers, its changes during the year and during the day, the short duration and randomness of the sporadic E layer lead to the fact that the conditions of sufficient refraction and total internal reflection necessary for the return of radio waves to the earth also arise randomly, last for a short time and not predicted.

The electron concentrations of various layers measured with geophysical rockets different time explain why ultra-long-range television reception is observed only within the first range (1st and 2nd television channels). The frequency of the waves of the subsequent ranges is higher and requires such electronic concentrations to return the wave to the ground, which do not exist in the layers. Waves of these ranges are not reflected from the ionosphere, but penetrate it through and through. The ultra-long-range reception of television programs is due to the appearance of the F2 layer and the sporadic layer E. However, the electron concentration of the normal E layer is insufficient to reflect the waves of the television range, therefore, ultra-long-range reception does not occur.

According to the laws of refraction, a ray incident on a refracting surface normally (at a right angle) is not refracted. The more gently the beam falls on the refracting surface, the more likely it is that the conditions for total internal reflection will be achieved, the lower the electron concentration is required for this. Therefore, ultra-long-range television reception is observed only at large distances (about 1000 km or more) from a television transmitter, and shorter distances for ultra-long-range reception form a dead zone.

The extent of the electron clouds and the electron concentration of the ionized layers vary within wide limits. Therefore, the field strength of the television signal also changes over a wide range when ultra-long-range reception appears. These limits are so wide that ultra-long reception is sometimes possible with good picture quality even when using indoor antennas as observed in 1957. However, the likelihood of obtaining a stable image with ultra-long reception increases with the use of high-performance antennas and high-sensitivity television receivers. Among such receivers, we can recommend a television set for long-range reception by N. Shvyrin, a description of which was given in the magazine "Radio" 12 for 1972. This television set is suitable for receiving signals with different image decomposition standards. However, it should be borne in mind that the construction of such a TV, and especially its adjustment and tuning, is available only to very experienced radio amateurs. In addition, an insufficiently detailed description was given in the journal. For experiments on ultra-long-range reception, you can also use a conventional television receiver for black-and-white images of industrial production, taking measures to improve its sensitivity.

As antennas, it is advisable to use narrow-band antennas with a high gain, for example, a two-row in-phase array of three-element loop antennas, built according to the dimensions for the first channel. It is advisable to install the antenna on a high mast, and if the length of the feeder exceeds 50 m, use a low-noise antenna amplifier, installing it on the mast in the immediate vicinity of the antenna. Due to the fact that it is not known in advance from which direction it will be possible to carry out ultra-long-range reception under the prevailing favorable conditions for signal propagation, it is necessary to be able to quickly and efficiently orient the antenna. For this, the antenna is installed on a swivel mast, which can rotate with a drive from a reversible electric motor equipped with a gearbox with a high transmission ratio. Thanks to such a gearbox, the engine power can be small, since the torque from the motor shaft increases in proportion to the gearbox transmission ratio. Naturally, the output gears of the reducer must be designed for high forces. To avoid twisting of the feeder, the antenna mast swing system must be equipped with motor power limit switches that limit the swing of the mast. The same limit switches can be used to signal the reaching of the maximum rotation of the antenna. Some radio amateurs supplement the remote antenna rotation system with a pair of selsyns. This makes it possible to determine the direction of the antenna in any of its positions using a scale installed on the axis of the selsyn-receiver.

Of course, in those cases where the installation for ultra-long-range reception is intended to receive television broadcasts from one specific television center, there is no need to rotate the antenna. In this case, the antenna is oriented towards the transmitter once and for all when it is installed.

ANTENNAS FOR RECEIVING LAND TELEVISION FROM THE CATALOG OF THE COMPANY "BELKA"

Annex 1

ANTENNAS FOR RECEIVING LAND TELEVISION FROM THE CATALOG OF THE COMPANY "BELKA"

Antennas for receiving terrestrial television are intended both for individual reception and for equipping systems for collective reception of television broadcasts from television centers and terrestrial repeaters. These antennas are classified into single-channel, single-band, dual-band, and wide-band antennas. Single-channel antennas are designed to receive only one specific program transmitted according to the frequency channel to which this antenna is tuned. Single-band antennas are designed to receive several programs that are transmitted at frequencies of one specific range: I meter (1, 2 channels), II meter (3 ... 5 channels), III meter (6 ... 12 channels) or IV-V decimeter (21 ... 80 channels). Dual-band antennas are capable of receiving signals from several programs in any of the two indicated ranges, and wide-range antennas - in more than two bands. Antennas designed to receive signals of range II (channels 3 ... 5) can also receive VHF-FM broadcasting signals.

All antennas listed below are passive, except for the AEZ-07 and 20 / 6-12 / 21-60 antennas, which contain wide-range antenna amplifiers. In the given data of each antenna, the gain value is given in relation to a half-wave vibrator. Coefficient of action shows the ratio of the levels of the main lobe of the antenna pattern to the level of its back lobe. For the most part, two brands of each antenna are indicated: according to the nomenclature of the "Belka" corporation and according to the manufacturer's nomenclature (for example: AE1-01 and DIPOL 5 / 3-5).

ANTENNA SINGLE-BAND

Channel numbers 3 ... 5 Gain, dB 3 ... 8 Type of signal polarization horizontal Number of elements 5 Coefficient of protective action, dB 8 Input resistance, Ohm 300 Weight, kg 1.6 Manufacturer brand DIPOL 5 / 3-5

Digital terrestrial television (DVB- Digital Video Broadcasting) is a transmission technology television picture and sound using digital video and sound coding. Digital coding, in contrast to analog, ensures signal delivery with minimal losses, since the signal is not affected by external interference. At the time of this writing, 20 digital channels are available, in the future this number should increase. This number of digital channels is not available in all regions, you can find out more precisely about the possibility of catching digital channels on the website www.rtrs.rf. If there are digital channels in your area, then it remains to make sure that your TV supports DVB-T2 technology (this can be found in the documentation for the TV) or buy a DVB-T2 set-top box and connect the antenna. The question arises - Which antenna to use for digital TV? or How to make an antenna for digital TV? 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 an antenna for digital television yourself.

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

In my opinion, the simplest antenna for digital television is a television cable. Everything is extremely simple, a coaxial cable is taken, an F connector and an adapter for connecting to a TV are put on one end, and the central core of the cable (a kind of whip antenna) is exposed at the other end. It remains only 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, for this go to the website www.rtrs.rf / when / here on the map find the tower closest to you and see how often digital channels broadcast.

More detailed information you will get it if you click the "Details" button.

Now you need to calculate the wavelength. The formula is quite simple:

where, λ (lambda) is the wavelength,

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

F - frequency in hertz

or easier 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 the coaxial cable is not beautiful and inconvenient, so I will leave half, or even a quarter of the wavelength.

l = λ * k / 2

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

λ- wavelength (calculated earlier)

k is the 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 strip 25 cm of the coaxial cable.

Here is the result of the work done

This is how the antenna looks when installed.

Aerial view while watching TV.

Seal

Delta H1381AF

The plots are located from the city at different distances of 10 km, 50 km and more, and the distance from the TV tower can be even greater and be 100 - 150 km. This is a significant distance, and an active antenna is needed for stable reception of digital television in the country.

Perhaps I'll start with the fact that stable reception at distances of up to 30 km can be provided by passive antennas, and in order to ensure stable reception both in summer and in winter at long distances, you need to use a more powerful one with an amplifier, and for hilly terrain, as well as over long-range reception, more and raise it higher using the mast.

To transmit a signal in digital TV, the decimeter range (UHF) is used with frequencies of 470 - 862 MHz (channels 21-69), therefore, when choosing an antenna for a summer residence, you need to focus on them. However, you should not rest only on this type, for the reception of the DVB T2 standard, all-wave (broadband) are also applicable, capable of receiving both the decimeter range and the meter 48 - 230 MHz.

Decimeter antenna for dvb t / t2 reception

Modern antennas are made of steel or aluminum and have an operating temperature range of -50 to +50 degrees with protection from external influences (snow, rain). Metal is heavier, but unlike aluminum, it is more reliable to deformation. Their forms are different, but the most effective, time-tested broadband antenna MV / UHF, is a wave channel. Such an antenna for a summer cottage for receiving digital TV is the best option.

The most common antennas today are "Delta" and "Locus". They have different gain factors (measured in decibels, dB) or adjustable, so you need to look at their characteristics. You need to understand that the en-na itself has its own gain, just like the amplifier.

The digital antennas and amplifiers offered by the sellers are nothing more than a publicity stunt. Amplifiers, if this is not some kind of special one, by their purpose they simply amplify the signal, in this case the television signal, in the entire frequency range of TV broadcasting. In the case of antennas, designating them as digital means that they are capable of receiving decimeter waves.

When installing the antenna on a mast, be sure to use grounding, even if the metal mast is on the ground. This will help the static electricity to drain into the ground during a thunderstorm (and of course when struck by lightning), which will prevent damage to the amplifier. Grounding the array (reflector) of the Polish antenna improves its performance, since it reflects the signal back to the vibrators, which amplifies it.

If you intend to do active antenna independently, then in the "network" you can find many different solutions, even from beer cans, the only question is whether they will work effectively and I advise you not to waste time, they are not so expensive. For example, an inexpensive so-called "Polish" for receiving digital television in the country, with a distance of up to 100 - 120 km, will be the very thing.

Antenna amplifiers

In the "Polish" all-wave antennas, SWA amplifiers are used with different gains, you need to purchase them separately, depending on how far from the tower. You can navigate by the proposed table:

Amplifier type	Range (km)	Gain (dB)	Coefficient of noise
SWA - 3	10 -30	20.5 -28	3.1
= / = - 4 Lux	20 — 45	29 — 35	3.0
=/= — 5	10 — 40	25 — 31	3.1
=/= — 6	10 — 40	25 — 30	3.1
=/= — 7	30 — 70	25 — 32	3.0
=/= — 9	30 — 70	21 — 31	3.1
=/= — 10	8 — 30	22 — 27	1.9
=/= — 14	30 — 70	28 — 37	2.8
=/= — 15	30 — 80	35 — 43	2.8
=/= — 17	30 — 100	35 — 42	2.9
=/= — 19	30 — 100	33 — 42	2.9
= / = - 555 Lux	50 — 100	34 — 43	2.2
= / = - 777 Lux	50 — 100	34 — 45	2.3
=/= — 999	80 — 120	33 — 45	2.9
=/= — 5555	80 — 120	34 — 45	2.9
=/= — 7777	100 -120	34 — 45	2.8
=/= — 9999	100 — 120	35 — 47	2.9
=/= — 2000	100 — 130	40 — 47	2.8
=/= — 3501	100 — 130	40 — 48	2.0
=/= — 6000	80 — 140	50 — 52	1.2
=/= — 9000	20 — 100	10 — 40	1.5
=/= — 9001	100 — 150	42 — 54	1.5
=/= — 9501	70 — 120	42 — 50	1.7

So let's summarize. If you need an antenna for a TV at your dacha, then with a distance from the TV tower of 10 to 30 km, we choose among indoor active ones, with a greater distance, we choose among street (outdoor) ones. The greater the distance, the greater the gain should be. Nothing bad will happen if the antenna for the summer residence has a slightly higher gain than necessary, so to speak, the margin will not hurt and then 10 or 20 channels (depending on the region) will show without problems.

Today we are sharing life hacks on how to make a TV antenna with our own hands. An antenna is a device for emitting or receiving radio waves. There are transmitting, receiving and receiving and receiving. The editors learned that a simple design can be made with copper and brass wire, copper tubes, wires, and even tin cans.

Tin can TV antenna

An antenna for a TV can be made by yourself, from scrap materials, even from empty beer cans. This method is the fastest and easiest. You can make a structure from electrodes and discs. Maximum amount there will be seven channels.

You will need:

1. can;
2. plug;
3. antenna cable;
4. screwdriver;
5. sticky tape or insulating tape;
6. wooden tremp;
7. self-tapping screws (2 pcs).

Room design guarantees confident reception analog signal within the city and without agreement for a cable (with a length of up to 2 m).

Distance between banks:

where λ is the wavelength. There should be no more than 3-4 dipoles. If there are fewer of them, the gain will be insignificant, more - there will be problems with the cable matching.

The signal quality will noticeably improve if you place a screen from the back of the metal mesh.

Distance between screen and main structure:

How to make a structure:

How to improve the antenna?

An amplifier is needed if the translator is far away. With an amplifier, the design receives the signal more reliably, but the "do it yourself" option may not play here.

You can use a magnet on which several turns of a television cable will be wound (it is assembled both near the TV and on the antenna).

If the question is how to amplify the signal of a home structure so that 20 channels are clearly broadcast instead of 7, it is necessary:

• buy a special TV signal preamplifier;
• find a place of ideal signal reception;
• get rid of the interference that metal objects create.

How to make a quick antenna:

How to assemble an antenna for digital TV?

A homemade design should be:

1. neatly manufactured with a high degree of accuracy without loss of electrical power of the signal;
2. strictly directed along the axis of the electromagnetic wave emanating from the transmitting center;
3. targeted by the type of polarization;
4. have protection against side interference signals of the same frequency emanating from any sources: electric motors, radio transmitters, generators.

How to make your own antenna for digital TV (DVB T2):

Simple digital TV antenna: what are the options?

It will require a piece of coaxial cable with a characteristic impedance of 75 ohms and a plug for connecting the structure.

The algorithm is as follows:

1. with an ordinary knife, the outer shell is cut off from the free end;
2. take the length with a small margin, since a small segment during adjustment is easier to bite off than to run after a new cable;
3. the shielding layer is removed from this section of the cable, the inner core is exposed and the insulation is removed;
4. insert the socket of the plug into the connector on the TV signal set-top box, direct the bare wire of the inner core across the incoming electromagnetic wave;
5. remember about horizontal polarization;
6. the terrestrial digital antenna should be fixed on the windowsill or with a piece of tape on the glass;
7. interference and reflected signals are shielded by a strip of foil located at a short distance from the central core;

Types of antennas and which of them can you make yourself?

There are "Polish", "eight" and "square". The digital antennas for the TV tuner and set-top box must be tuned to the same frequency.

IMPORTANT! Both the set-top box and the tuner must be able to decode the signal.

"Polish" antenna and digital TV

It provides high-quality and reliable reception analog television(+ UHF), but completely unsuitable for receiving modern digital TV.

"Eight": manufacturing algorithm

Uncomplicated design for DVB T2, which can be made from Ø 3 mm copper wire. The reflector is not used in this case. The upper side of the segments is 14 cm, the lateral side is 13 cm.

We measure out the wire 112 cm long and start bending:

1. We bend the 1st segment with a length of 14 cm (for the antenna - 13 cm and 1 cm for the strength of the loop);
2. 2nd and 3rd, like 6 and 7 - 14 cm;
3. 4th and 5th - 13 cm;
4. 8th - 14 cm - 13 cm and 1 cm - with a loop of strength.

We clean the hinges, twist and solder them - they will become contacts for connecting the cable. For soldering, we strip the cable from the antenna side by 2 cm and 1 cm - from the plug side, the joints are sealed with any elastic hot melt glue.

What is a "square" and is it worth it to tackle it yourself?

A modification of the "three squares" design with 6 elements and a transformer, it confidently receives digital and analogue channels at a distance of up to 10 km of line of sight.

• Double square

Behind the main frame is the reflector, the side of the main frame is 0.254λ, the side of the reflector is 0.278λ, the distance between the frames is 0.089λ.

Another option for a double square is two rings.

Butterfly antenna

A shortwave small-sized antenna, shaped like a butterfly. To make it, you need copper wireØ about 2 mm, for external use 4 mm is also allowed, for home use - a television ordinary coaxial cable 75 Ohm.

Rectangular wire frame (length and width):

1. for TV - 500x200 mm;
2. for Wi-fi (omnidirectional) and Bluetooth - 90x30 mm.

We twist the frame crosswise and cut it with pliers so that two triangles are formed. We solder the coaxial cable and fix it with staples (tape) to the dielectric ebonite, wood or plastic.

Powerful TV Antenna: What Should I Know About It?

In order for the device to function like a conventional antenna, its receiving circuit needs to be improved.

Algorithm:

1. we buy equipment for signal amplification;
2. we connect to the device to eliminate signal interference;
3. we wrap the cable with insulating tape from both ends;
4. we make a screen for high-quality reception: a kind of metal mesh, which is isolated from the TV and fixed behind the receiver;
5. for the screen, an ordinary metal mesh from an ordinary fence will come down;
6. add iron rods and connect them symmetrically to the shield to amplify the signal (it is necessary that the entire structure is of the same type of metal to avoid oxidation) $
7. place another amplifier in the center of the installation and solder the contacts to the receiver.

IMPORTANT! Such a television structure is installed on the roof with a reference point to the nearest television tower.

Versatile design

Required tools and materials:

• copper wire (length 4 m, cross section 4 mm2);
• board of any thickness, but 7 cm wide, 55 cm long;
• soldering iron;
• wood screws;
• tape measure or ruler;
• screwdriver;
• simple pencil.

Algorithm:

1. cut the copper wire into 8 parts, the length of each is 37.5 cm;
2. remove the insulating layer in the middle of each of the resulting wire parts;
3. cut off 2 more copper wires (22 cm each) and divide them conditionally into 3 equal parts;
4. remove the insulating layer at the points of inflection;
5. we bend the wire in prepared (bare) places;
6. the distance between the ends of the wire bent in half is 7.5 cm;
7. fix the plug, connect the TV cable.

How to make an antenna for digital TV (DVB T2) yourself:

Log-periodic (all-wave) design

This is a collecting line with halves of dipoles installed alternately on it. The length of a piece of wire forming a half-dipole will be λ / 4.

IMPORTANT! Hand-made outdoor structures can give an amplification of up to 25 dB, about 12 dB indoor.

LPA is the ideal device for receiving both analogue and digital signals. To calculate the parameters, it is necessary to know the value of the progression index (from 0.7 to 0.9) and the value of the opening angle α (30-60 °). We take the proportion as a basis and calculate the required parameters:

τ = B2 / B1 = B3 / B2 = Bn / (B (n-1)) = A2 / A1 = A3 / A2 = An / (A (n-1))

The higher the τ, the better the gain. Decreasing the angle α can increase the directivity.

Calculation of parameters:

1. determine the values ​​of B2 and A2;
2. calculate B1 and A1 and other parameters.

What types of antennas are there? Home simple homemade antenna

Home construction is assembled from copper or brass wire. Aluminum is not suitable because it quickly oxidizes.

The wire is cleaned from both ends of the insulating material, one end is attached to a pipe or battery, the opposite is inserted into the television connector. Amplifier required frequencies a pipe protrudes, which runs through the whole house and goes upstairs. A signal immediately appears, the antenna catches 5 channels.

• For an apartment with a balcony

The wire is taken longer, since the TV and the balcony area will need to be connected. The wire is stripped on both sides, one end is connected to the TV in a cable socket, and the other is pulled onto the balcony and attached to ropes or strings. Such an antenna gives a better image, and there are more channels with it.

Antenna for summer cottages

Stable signal reception at a distance of up to 30 km is installed by passive structures both in winter and in summer. For long distances, more powerful structures are needed, better with an amplifier. For hilly terrain and ultra-long range reception, the antenna must be raised higher using a mast.

For classic design for a summer residence you will need:

1. wire (Ø 1.5 mm) - at the rate of 1.5-2 m for the antenna and 5-6 m for the distance from the structure to the TV;
   2. outer part made of prepared wire (screw 1-1.5 m into a ring, Ø from 356 mm to 450 mm);
2. the inner part of the antenna (make a second ring from the wire, dimensions - 180 mm;
3. ready-made rings - the basis of the future antenna - are fixed on a piece of plywood (a piece of wood is also possible), but so that the tree does not overlap the rings and does not dangle;
4. orient the finished structure with the rings in the direction of the signal source, turn the antenna to search for the best signal.

Antenna Kharchenko (biquadrat)

It is an outdoor zigzag design with a reflector.

Z-antenna system with reflector provides the same parameters as
LP antenna. The difference lies in the main lobe - it is twice as long horizontally, which allows you to catch a signal from all directions.

The UHF antenna is made of a copper tube and a sheet of aluminum 6 mm thick.

Car antenna: internal and external

• Internal

You will need a frame device, which is laid at the back under the glass seal. In the upper part, it is narrower, but the dimensions are not the same as those required at a frequency of 27 MHz. For this reason, a capacitor is installed in the center, with the help of which the TV antenna for the car is tuned into resonance on the required channel.

IMPORTANT! There are several receiving frequencies - 27 and 65 MHz, 28.2 and 68 MHz.

Manufacturing algorithm:

1. we take the MGTF 0.5 wire, which is laid along the edges of the rear window in the form of a trapezoid;
2. do the same with the upper part;
3. the poles are positioned so that it is easy to add wires for the matching capacitor;
4. to remove the signal, use the RK-50 cable;
5. in the center of the rear window, 5-25 PF are fixed, to which both cables are strictly vertically directed.

Universal compact TV antenna for the car:

• External

For a good signal, you need to attach a pair of telescopic antennas from the radio receiver. The case can be taken from the Polish device.

Figure 11 - Polish design - base for internal auto antenna

Power supply to the amplifier:

1. we take a connector for an active TV antenna and solder a wire to it;
2. we pass the cable from the TV antenna so as not to pinch it;
3. screw it to the connector;
4. the wire soldered to the connector is connected to the +12 output on the radio to turn on the amplifier or active antenna.

There are active in-car combo TV antennas with external elements for the reception of MV / UHF.

In addition to the above, there are meter (crossed aluminum tubes) and fractal antennas.

DIY fractal Wi-fi antenna:

IMPORTANT! All stories about effective work a mercury antenna is a big misconception. Science does not know a single principle by which a mercury antenna could work. Editors warn that making a mercury antenna yourself is a so-so idea and a dangerous undertaking.

What is digital TV multiplex?

A digital multiplex is a set of channels of the same frequency. There are two multiplexes: the first is available in all cities with digital TV, but not all towers are ready for the second. For installation, you need a receiver and an antenna with DVB support T2.

Previous analogue broadcasting has been completely discontinued since 2009. The change to digital format created the need for an appropriate receiving device. Digital TV broadcasting is carried out in the UHF range, which is capable of accommodating many channels, having a compactness and high signal quality. The increased transmission rate reduced equipment maintenance costs and made it more resistant to interference, although not all problems were completely resolved. In rural areas, signal reception is almost impossible, but in a big city it becomes more difficult due to the ability of the reinforced concrete structures of multi-storey buildings to screen the signal. For confident reception, it is quite possible to make an antenna for digital TV with your own hands, since its cost in the store is quite high.

How a digital antenna works

A digital signal differs from an analog one in that it does not transmit the wave itself, but information about it... That is, it consists of a continuous stream of "coordinates" of points of a specific sinusoid graph transmitted by conventional analog devices. This makes it possible to significantly reduce interference and improve the quality of signal transmission, since a failure in the transmission of information does not cause major problems and is calmly corrected when decoding the signal in the receiver. Otherwise, the transmission technology remains the same - from the transmitter they are emitted into space electromagnetic vibrations, they are received by antennas in the line of sight, on the contours of which a small voltage arises, which is transmitted to the decoding device of the TV and turns into image and sound.

To receive decimeter waves, a small antenna size is required, which compares favorably with the previously used huge antennas that filled the roofs of houses. The dimensions of digital antennas are quite compact, so they can be freely placed in an apartment, on a balcony or other convenient for the owner and providing quality reception location. A homemade antenna has a simple design and is quite accessible for manufacturing for people without special training, who have only basic knowledge.

Do-it-yourself loop antenna

A circular antenna for digital TV has the highest input impedance

A loop antenna is one of the simplest options. At the same time, the resistance to interference of such a device is very high, because the design combines a receiving antenna and an interference filter. The name "frame" refers to a specific configuration - it is a closed contour in the form of a round or rectangular frame. Made from copper wire. Also, as an option, you can use a piece antenna cable(RG6), vinyl-free.

Payment

To calculate the loop antenna, you only need to determine the length of the wire from which the frame is made... The calculation formula looks like this:

where LR is the length of the wire in the loop,

f - wave coefficient, which is the arithmetic mean between the values ​​of the boundaries of the wave range. For example, if the broadcast is in the 568-720 MHz range, then f = 568 + 720/2 = 644.

You can find out the required ranges on the websites of the transmitting companies or from other sources - this information is freely distributed. The start and end frequencies are used for the calculation. If there is no final one, then the value of f is taken equal to the initial frequency.

Some experts give another version of the formula, according to which the side of the square frame is equal to 0.254 of the wavelength (or f). That is, the value obtained from the calculation according to the first formula must be increased by 1.5%. The difference is subtle, but in some cases it is important.

To make an antenna you will need:

• Pliers;
• Ruler;
• Soldering iron;
• A utility knife for stripping the insulation (if using an antenna cable).

Only the most basic tools are listed, depending on the skills and capabilities of the user, others, more suitable for any purpose, can be used.

Manufacturing instruction

Making a loop antenna is straightforward. You will need to do the following:

• Cut a piece of wire to the desired length. Experienced users are advised to first cut a piece a little longer than the calculation requires, so that it is possible to more accurately adjust the length when forming the antenna configuration.
• Shape the antenna into the desired shape. If a round loop is used, then it is necessary to make the circle as even as possible; for a square frame, the length of the sides should be exactly maintained.
• The ends of the frame are connected to the antenna wire from the TV: one end to the braid, the other to the central core. This task requires a soldering iron or a terminal block.
• It remains to install the device in the most suitable place for reception and adjust the position.

How to make an antenna Kharchenko

You can make such an antenna with your own hands for Wi-Fi reception

The design was proposed by K.P. Kharchenko in 1961. The main task is to receive television broadcasts, but practice has shown the high suitability and versatility of the invention. The external antenna of Kharchenko has the shape of a figure of eight with an open middle. It consists of two squares, and the connection to the antenna wire is made at the midpoints. Thus, we have a closed loop of thick copper wire, which has a specific shape. The difference from the frame structure lies precisely in the more complex configuration, which allows to obtain stable and reliable signal reception, noise immunity and reliability. Its feature is broadband and the ability to receive both television and radio signals. It all depends on the location of the antenna - the vertical one receives the TV signal, the horizontal one - the radio.

The figure of eight is not the only possible option, you can increase the number of formed squares. Variants with the formation of circles, triangles, etc. are also known. The eight is used due to the simplicity of manufacture and adjustment, as well as the absence of interference.

Payment

Self-calculation of the Kharchenko antenna is not difficult, but includes the determination of many quantities. You will need to calculate the length of the side of the square, the size of the reflector (reflector), the total length of the figure eight from the top to the bottom point, the size of the gap between the reflector and the antenna, etc. Therefore, the simplest and most reliable solution will be to use an online calculator, of which there are many on the net. To get a more accurate result, you can try to count on several services and compare the data.

Required tools and materials

To assemble the Kharchenko antenna you will need:

• Thick copper wire with a cross section of about 4 mm 2;
• Aluminum plate for reflector (reflector). In its absence, a metal grid (mesh) can be used as a reflector;
• Pliers, hammer, screwdriver;
• Electric drill with a set of drills;
• Soldering iron, terminal block;
• A metal pipe or wooden long bars for the manufacture of a supporting structure (mast).

There are many design options for the manufacture of which you can use various accessories. If necessary, they are involved in the working order.

Manufacturing instruction

• According to the calculated data, an eight is made.
• The connection at the midpoint is soldered, the second point is tinned for the subsequent connection of the power supply.
• Holes are drilled in the reflector plate into which the bosses are installed for attaching the antenna.
• It is fixed on the support bosses, a wire is soldered to the central points.
• The reflector plate is attached to the mast. For this, screws or clamps are used if it is made of a metal pipe.
• The mast with the antenna is installed in the designated place.
• It is connected to the TV, the optimal position is adjusted.

Other options

A variant of the design of the Sotnikov antenna from three squares

The options considered are not the only possible ones. There are many designs of antennas for receiving a television signal.

The following can be distinguished:

• Three-element wave channel. It is a rather complex structure of a horizontal strip, on which two transverse stripes and a T-shaped frame are installed. A variant of this design is a four-piece wave channel containing three crossbars and one T-shaped structure.
• Double square (Sotnikov antenna). Has a gain of 10-13 dB, it is represented by two square frames, located in parallel and connected by a crossbar. A variant of the design is a triple square, the authorship of which belongs to the same Sotnikov. The reinforcing ability is higher - in the region of 14-15 dB.
• Turkin's antenna. The amplification factor possessed by such a design is more than 15 dB. It consists of six rings of different diameters, fixed on a horizontal dielectric support rod. The device requires a rather careful calculation of the diameter of the rings and the distance between them.

Video: How to make an antenna for digital TV with your own hands

Transition of television to digital format occurred with the aim of eliminating interference, increasing the quality of transmission, more confident reception and compactness of the equipment. The need to use your own antenna is due to large quantity interference or distance from the repeater. In the absence of the possibility of acquiring a factory-made sample, which is quite expensive and not always commercially available, it is quite possible to make a home-made device, since there is no particular difficulty in this.