Antenna for receiving digital signals, calculated and assembled by engineer Kharchenko, outwardly looks like an ordinary double square made of thick copper wire. With their open corners, these squares are combined into a common contour, and a television cable outlet is soldered to the zone of their joining (figure below).
Kharchenko's do-it-yourself classic UHF antenna, made at home, in addition to two squares, contains a reflector made of conductive material (it allows you to increase the efficiency of directional reception).
Under certain conditions, such an antenna can be used to receive ultra-high frequencies of mobile channels in 3g format, in particular.
Antenna Design Features
decimeter version
A design feature of the Kharchenko antenna is a fixed ratio between the perimeter of each of its two squares and the length of the received waves (they must be equal). To obtain the desired induced field strength, it is also important to correctly select the diameter of the loop wire.
Since broadcasting was previously focused on the meter range, a wire with a diameter of about 12 cm would be required to receive such a signal. In this case, the zigzag antenna turned out to be too bulky and inconvenient to use, and its dimensions would not allow it to be used at home.
Kharchenko's zigzag antennas experienced their second birth at the time of the on-air broadcasting in the decimeter bands.
Additional Information. A zigzag antenna designed to receive a UHF signal must have fixed dimensions, which will be discussed in the following sections.
The wave impedance for which such self-made structures are calculated is usually on the order of 50 ohms. This indicator, however, is in good agreement with a typical coaxial line with a corresponding parameter equal to 50 (75) ohms. To expand the bandwidth of the television signal, such an antenna was made not from a simple wire, but from a flat copper or aluminum bus, the individual parts of which were connected into a biquad with pre-selected aluminum rivets (photo below).
At the junction of copper strips, the UHF antenna was additionally soldered; at the same time, the distance between the rivets was taken as its length. In those cases when, for the purpose of reliable reception, it was necessary to use a standard antenna amplifier, the developers dispensed with the second square (one was enough for reliable reception).
Execution in DVB-T2 standard
Digital broadcasting, designated by the “dvb t2” standard, is conducted, as you know, at the frequencies of the decimeter range corresponding to TV channels from 21 to 69, using the “multiplex” format. In many cities of Russia, local television stations are gradually switching to the dvb TV broadcast format, which causes a certain interest in ensuring its reliable reception.
In this regard, the user must be aware that a home-made design for t2 must have the same dimensions as a classic antenna for decimeter digital broadcasting.
Important! Modern television receivers, which include an antenna for a digital signal, can attenuate it when the transmitting station is close.
In special situations, when the transmitter for the t2 range is very close, using the old frame design, you will either have to completely remove the second square (or screen), or choose a less sensitive amplifier.
The following solutions can be chosen as options for the manufacture of dtsv designs:
- Make a brand new receiving device for t2 with your own hands;
- Try to build a combined antenna containing an element in the form of a circle of wire 55.5 cm long (see photo below);
- With its help it will be possible to accept all known formats (including 3g mobile communications).
In the case when it is necessary to make a structure for receiving Internet signals, including Bluetooth, WiFi (3g, 4g) or mobile communication channels operating on ultrashort waves, the dimensions of such an antenna will be quite miniature.
The dimensions of the antenna for 3g due to the high frequency will be limited to a length of 10 centimeters, and all possible varieties of a home-made product can be assembled using the same drawing.
Significant differences concerning all options version of the miniature antenna (for Bluetooth or for cell phone), will appear only in the dimensions of the receiving structure itself.
Additional Information. If you need to calculate such an antenna, you can use the online calculator.
The calculation order in this case is set by the method of using a specific network resource (these methods are widely represented on the network both for t2 and for other TV signal formats).
Self-manufacturing
UHF antenna
After the Kharchenko antenna for the TV has been calculated, it will be possible to proceed to its manufacture with your own hands.
In order to make an antenna with high quality, the following material and tools will be required:
- Thick single-core wire (it is better if it is copper);
- Electric soldering iron, ordinary pliers, as well as a ruler and quick-setting glue;
- A piece of cable with Rwave equal to 50 ohms;
- Foil fiberglass, an old DVD (CD) disc and / or, in extreme cases, a sprat can (they are needed to make a reflective screen zigzag antenna).
And, finally, a special padding post should be made that sets the desired distance between the antenna bus and the screen (a plastic bottle cap can be used as such a pad).
The whole procedure, during which the antenna is made by hand, is best broken down into a number of stages, namely:
- First you need to remove the protective insulation from the copper wire;
- Then, using a ruler, clearly mark the places of future bends of the TV antenna;
- After that, with the help of pliers, bend the wire in the previously marked places;
Note! The more accurately the wire marking is done and the more accurate the bends, the antenna for digital television it will be better to receive the signal.
- Upon completion of the molding of the frame, the areas for attaching the antenna cable are carefully tinned with a soldering iron;
- Then the lead wire is soldered to the tinned area, but first a stand and a protective screen are strung in series on the cable segment;
- At the final stage of assembly, the entire resulting structure is glued with standard silicone (figure below).
Upgrading WiFi and Bluetooth
It is known that the WiFi signal is transmitted, like other types of terrestrial communications, over a radio channel, which allows the use of an antenna design to improve the reception of a router or similar devices. According to a number of craftsmen from among the developers of 3g antennas, if a parabolic dish is taken as a screen in the design discussed above, the gain at WiFi frequencies can be increased to 31 dB.
Additional Information. Such a screen can be made from a tin can bent in a certain way.
In the manufacture of a reflector for 3g or WiFi, the curvature of its surface is usually selected experimentally. To do this, a program must be installed on the transceiver device (router, for example) that can fix the level of the signal entering the device.
Using such a program, it will be possible, by changing the curvature of the surface of a home-made screen, to monitor all changes in the gain (in real time).
Calculation technology
The calculation of parameters in this case is focused on the operating frequency of 2445 MHz (see photo).
Note that in order to calculate such an antenna, it will be necessary to know its following characteristic dimensions:
- Copper flat wire diameter - 2.5 mm;
- The volume of the stock of all material (wire 256.6 mm long);
- L1 - the outer side of one square, equal to approximately 30.8 mm;
- L2 - its inner side (29.6 mm);
- L3 - length of the working frame (84 mm);
- L4 is its effective width (43 mm).
In addition, it will be necessary to calculate such a characteristic parameter as L5 (it is called the connection gap), which is usually chosen to be 1.9 mm. Add to this the height of the additional posts D - 13.6 mm, as well as the width of the screen B - 122 mm and, finally, its working length H - 122 mm.
Important! Antenna reception for router or mobile format will be the more confident, the more accurately all the above dimensions are maintained.
The screen can be made from a small piece of foil fiberglass left over from old boards. In order to increase the mechanical strength, it is additionally soldered to the braid of the signal-output cable. As a screen, it is customary to use an old CD with a thin layer of foil, on which useful information is usually recorded.
In this case, to assemble an antenna for digital TV, it will be possible to use an old box from under unnecessary CDs.
Good specialists will calculate the data, using their own experience and homework for this. But non-specialists will have to resort to the help of online calculators widely represented in the open network or their analogues.
In the final part of the review on how to make the Kharchenko antenna yourself, we note the following important points this enterprise. Before starting its independent production, the main thing is to correctly take into account all its characteristic parameters and indicators (including the reception of the 3g format and a number of other microwave signals).
Only under this condition, with the help of such a relatively simple homemade product, it is possible to receive a UHF signal at a decent distance from the television center (at distances of up to 2 kilometers).
Video
With DVB-T2 support, and of course, he needed an antenna, which naturally needs to be made by hand. How to make an antenna for DVB-T2 with your own hands will be discussed further.
To begin with, I decided to test the Kharchenko biquadrat antenna, or simply the "eight" in common people. For manufacturing, we need a copper or aluminum wire with a diameter of 2-5 mm. I had a 2.5 square VVG at hand and I decided to try to make an antenna for DVB-T2 from it.
Antenna calculation
We will find out our frequencies of both DVB-T2 packages in our area. For this you can go to the website of the Interactive map of CETV and see which tower is closer to you, one or both packages of channels are broadcasting and at what frequencies. In our suburbs of St. Petersburg, these are 586 MHz and 666 MHz.
Now, knowing the packet frequencies, we need to calculate the length of the side of the square of our DVB-T2 antenna. It is equal to a quarter of a wavelength.
That is, for our 586MHz: 300000000/586000000=0,51 meter. Quarter wavelength respectively 0,51/4=0,127 meters or 12,7 cm.
For the second 666 MHz multiplex, we calculate similarly and get 11,2 cm.
We are interested in L1. H and B for an antenna with a reflector (grid), amplifies the signal. I did without it.
Now if we make an antenna for two DVB-T2 channel packages, we determine the average length. That is, we add our lengths and divide in half.
L1=(12.7+11.2)/2=11.95 round up to 12 cm.
Antenna assembly for DVB-T2
Everything should be clear here. We take our segment of VVG or whatever you have. To determine the approximate length of the wire needed to assemble the antenna, you can L1 * 8 and throw a couple of centimeters. 12*8+2=98 cm was needed to make my antenna.
If you have a thick wire 4-5 mm in diameter, then most likely you will not be able to do without a vice. I had enough pliers.
We clean the wire from insulation. Then bend the biquadrat with pliers. Let's see the pictures. All angles are 90 degrees.
Then solder the 75 ohm TV cable. We solder the core to one square, the braid to another.
The signal at high frequencies propagates along the surface of the conductor, so it is better to paint the antenna after assembly. I used leftover acrylic facade paint. It is better to fill the place of soldering with hot-melt adhesive or sealant.
We fasten the wire from the place of soldering with ties (straps) along the sides of the square, as in the photo. This mandatory action is antenna matching.
Testing a homemade antenna on a homemade TV
So the biquadrate gives a signal amplification of the order of 6 dB, and up to the tower 26 km in a straight line. Although the CETV website indicates that we are in the zone of a confident signal, I doubted and prepared what I had done a long time ago.
He climbed to the second floor of the house and pulled out the antenna to the scaffolding. He pointed towards the tower and turned on the TV. The TV confidently received both digital TV packages.
I brought a homemade antenna into the house, the TV continued to confidently show perfectly.
K. Kharchenko
Reception of television broadcasts at radio frequencies 470 ... 622 MHz (21-39 channels) of the decimeter wave range (DCW) requires an appropriate approach to the calculation and design of antenna devices.
Some radio amateurs are trying to solve this problem by simply recalculating, based on the principles of electrodynamic similarity of antennas, the parameters of existing designs of television antennas in the meter range (channels 1-12). At the same time, they inevitably face the difficulties of the recalculation itself and often do not get the desired results.
What are the basic principles of approach to solving this problem?
In free space, the radio waves emitted by the antenna have a spherical divergence, as a result of which the electric field strength E decreases inversely with the distance r from the antenna.
In real conditions, propagating radio waves undergo greater attenuation than that existing in free space. To take into account this attenuation, an attenuation factor F(r) = E / Eb is introduced, which characterizes the ratio of the field strength for real conditions to the field strength of free space at equal distances, identical antennas and powers supplied to them, etc. Using the attenuation multiplier the field strength produced by a transmitting antenna under real conditions at a distance r can be expressed as
The receiving antenna converts the energy of the electromagnetic wave into an electrical signal. Quantitatively, this ability of the antenna is characterized by its effective area Seff. It corresponds to the area of the wave front from which all the energy contained in it is absorbed. This area is related to the CPV by the relation:
The foregoing allows us to write a radio transmission equation that relates the parameters of communication equipment (transmitter and receiver) and antennas and determines the signal level on the path: at transmitter power P1, signal power P2 at the receiver input will be equal to
The factor in this expression, enclosed in brackets, determines the basic propagation loss of the radio waves (basic transmission loss). It is assumed that the antenna is matched with the feeder, and the feeder with the television receiver and, in addition, the antenna is matched in polarization with the signal field.
Let us consider expression (11) in more detail.
This specific example shows that with an increase in the frequency (reduction in the wavelength) of television transmissions, the power of the signal entering the TV input, all other things being equal, decreases rapidly, i.e., the reception conditions deteriorate. On the transmission side, they try to compensate for these troubles by increasing the product P1U1. But in real conditions, the factor F(r) and the efficiency of the receiving feeder decrease with increasing frequency, so the need to increase the gain of the receiving antenna Y2 becomes inevitable. This conclusion entails another one, which is that, as a rule, for reliable reception of programs from 21-39 television channels, it is necessary to use new, more directional antennas compared to antennas used in the wavelength range of channels 1-5.
In an effort to get stable TV reception, radio amateurs are forced to complicate antennas, for example, to build antenna arrays, that is, they combine several antennas of the same type that have proven themselves in practice (each of which has its own pair of power points) with a common power system and only one (common for all) a pair of power points. At the same time, they often underestimate the importance of the matching stage in the construction of antenna arrays, which is associated with relatively complex measurements. Let us illustrate this with a specific example.
A similar effect is also obtained when three elements are connected in parallel (Fig. 1, c). Continuing such reasoning, we can obtain the dependence illustrated in Fig. 2.
Here effective area antenna is directly proportional to the number n of radiators in the array, as well as the power absorbed by the antenna P sums. The power Р pr supplied to the receiver, with an increase in the number n, asymptotically approaches 4Рo. This example shows the futility of attempts to increase the gain of the antenna array without taking into account the coordination of its elements with the feeder. Difficulties associated with matching are overcome either by using special matching devices or by choosing special types of antennas. For example, in the decimeter and especially in the centimeter wavelength ranges, as a rule, so-called aperture antennas are used, that is, horn or parabolic. The peculiarity of such antennas lies in the fact that they have a simple, "small" feed, and a "large", relatively complex reflector. A large reflector determines the directional properties of the antenna, determines its directivity factor.
It is not possible to make aperture-type antennas for the DTSV range in amateur conditions, since they are bulky and complex. But some semblance of an aperture antenna can be constructed by assuming a feed in the form of a well-known zigzag antenna (z-antenna). The fabric of such an antenna consists of eight closed identical conductors, which form two diamond-shaped cells (Fig. 3).
For the formation of the antenna radiation pattern, in particular, it is necessary that the radiators are in phase and spaced relative to each other. The Z-antenna has one pair of feed points (a-b), to which the feeder is directly connected. Thanks to this design of the antenna, its conductors are excited in such a way (a special case of the direction of currents on the antenna conductors in Fig. 3 is shown by arrows) that a kind of in-phase array of four vibrators is formed. At points P-P conductors the antenna webs are closed to each other and there is always a current antinode. The antenna has linear polarization. The orientation of the electric field vector E in fig. 3 is shown by arrows.
The radiation patterns of the s-antenna satisfy the frequency range with overlap fmax/fmin =2-2.5. Its directivity depends little on the change in the angle a (alpha), since with its increase, the decrease in the directivity of the antenna in the H plane is compensated by an increase in the directivity in the E plane, and vice versa. The directivity characteristic of the s-antenna is symmetrical with respect to the plane in which the conductors of its web are located.
Due to the fact that at the P-P points there is no break in the conductors of the antenna web, then there are points of zero potential (voltage zeros and current maxima) regardless of the wavelength. This circumstance makes it possible to do without a special balancing device when powered by a coaxial cable.
The cable is laid through the point of zero potential P and the two conductors of the antenna web are led to its power points (Fig. 4). Here, the cable braid is connected to one of the antenna feed points, and the center conductor is connected to the other. In principle, the cable braid at point P also needs to be short-circuited to the antenna web, however, as practice has shown, this is not necessary. It is enough to move the cable to the wires of the antenna web at point P, without breaking its PVC sheath.
The zigzag antenna is broadband and convenient because its design is relatively simple. This property allows it to allow significant deviations (inevitable during manufacture) in one direction or another from the calculated dimensions of its elements with virtually no violation of electrical parameters.
Curve 1 shown in Fig. 5, characterizes the dependence of KBV on
Using the graphs in Fig. 5, it is possible to build a s-antenna having the highest possible directivity factor for of this type antenna sheets. Its input impedance in the frequency range largely depends on the transverse dimensions of the conductors from which the web is made. The thicker (wider) the conductors, the better the matching of the antenna with the feeder. In general, conductors of a wide variety of profiles are suitable for the web of an s-antenna - tubes, plates, corners, etc.
The operating range of the s-antenna can be extended towards lower frequencies without increasing the size L by forming an additional distributed capacitance of the conductors of its web, and the overall dimensions, expressed in the wavelengths of the maximum wavelength of the operating range, can be reduced. This is achieved by bridging part of the conductors of the s-antenna, for example, with additional conductors (Fig. 6),
Which create additional distributed capacity.
The radiation patterns of such an antenna in the E plane are similar to those of a dipole. In the H plane, the radiation patterns undergo significant changes with increasing frequency. So, at the beginning of the operating frequency range, they are only slightly compressed at angles close to 90°, and at the end of the operating range, the field is practically absent in the sector of angles of ±40...140°.
To increase the directivity of an antenna consisting of a zigzag web, a flat reflector screen is used, which reflects part of the high-frequency energy incident on the screen towards the antenna web. In the plane of the web, the phase of the high-frequency field reflected by the reflector should be close to the phase of the field created by the web itself. In this case, the required fields are combined and the reflector screen approximately doubles the initial gain of the antenna. The phase of the reflected field depends on the shape and dimensions of the screen, as well as on the distance S between it and the antenna web.
As a rule, the dimensions of the screen are significant and the phase of the reflected field depends mainly on the distance S. In practice, the reflector is rarely made in the form of a single metal sheet. More often it is a series of conductors located in the same plane parallel to the field vector E.
The length of the conductors depends on the maximum wavelength (Lambda max) of the operating range and the dimensions of the active antenna web, which should not protrude beyond the screen. In the E plane, the reflector must necessarily be slightly more than half the maximum wavelength. The thicker the conductors from which the reflector is made, and the closer they are located to each other, the smaller part of the energy falling on it seeps into the rear half-space.
For design reasons, the screen should not be made very dense. It is enough that the distances between conductors with a diameter of 3 ... 5 mm do not exceed 0.05 ... 0.1 - the minimum wave of the operating range. The conductors that form the screen can be interconnected anywhere and even welded or soldered to the metal frame. If they are located in the plane of the reflector itself or behind it, then their influence on the operation of the reflector can be neglected.
In order to avoid additional interference, do not allow the conductors (antenna or reflector sheets) to rub or touch each other from the wind.
One of the possible options for an antenna with a reflector is shown in Fig. 7.
Its active canvas consists of flat conductors - strips, and the reflector - of tubes. But it can be completely metal. There must be reliable electrical contact at the junctions of the antenna elements.
The value of KBV in a path with a wave impedance of 75 Ohm is largely affected by both the width of the bar dpl (or the radius of the wire) of the active antenna web and the distance S at which it is removed from the screen.
With increasing distance S, the directivity of the antenna decreases and narrows the frequency range within which the directional properties of the s-antenna do not undergo noticeable changes. Thus, from the point of view of improving the directivity of the antenna, it is desirable to reduce the distance S, and from the point of view of matching, it is desirable to increase it.
Racks are used to attach the antenna web to a flat reflector. At points P-P (Fig. 6 and 7), the racks can be both metal and dielectric, and at points Y-U, they must be dielectric.
In a number of practical cases of receiving signals on 21-39 television channels, the available gain factor (KU) of a s-antenna with a flat screen may not be sufficient. To increase the KU, as already mentioned, it is possible to build an antenna array, for example, from two or four s-antennas with a flat screen. There is, however, another way to increase the gain - the complication of the shape of the reflector of the s-antenna.
We give an example of what a reflector of a s-antenna should be in order for its CG to correspond to the CG value of an in-phase antenna array built from four s-antennas. This way is the simplest and most accessible in amateur practice than building an antenna array.
In the drawings of the antenna, the dimensions of all its elements are indicated in relation to the reception of television programs on 21-39 channels.
The active fabric of the antenna shown in Fig. 6 is made of flat metal plates with a thickness of 1...2 mm, superimposed on each other "overlapped" and fastened with screws and nuts. There must be reliable electrical contact at the points of contact between the plates. Structurally, the active web of the antenna has axial symmetry, which allows it to be firmly fixed on a flat screen. For this, support racks are used, placing them in peaks P-P and U-U squareformed by the plates of the antenna web. P-P points have a "zero" potential with respect to the "ground", so the racks in these cars can be made of any material, including metal. U-U points have some potential with respect to the "ground", so the racks at these points should only be made of a dielectric (for example, plexiglass). The cable (feeder) to power points a-b is laid along a metal support to one (lower) point P and further along the sides of the antenna web (see Fig. 6). Particular attention should be paid to the orientation of the vector E, which characterizes the polarization properties of the antenna. The direction of the vector E coincides with the direction connecting the points a-b of the antenna feed. The gap between "points a-b" should be about 15 mm without notches and other traces of careless processing of the plates.
The basis of a flat reflector screen is a metal cross, on which, like on a frame, an active antenna sheet and screen conductors are placed. For the crosspiece, the antenna assembly is securely attached to the mast in such a way that it is raised above local interfering objects (Fig. 8).
In the manufacture of a "truncated horn" type reflector, all sides of a flat reflector are lengthened with flaps and bent so as to form a figure like a "dilapidated" box, in which the bottom is a flat screen, and the walls are flaps. On fig. 9
Such a three-dimensional reflector is shown in three projections with all dimensions. It can be made from metal tubes, plates, rolled products of various profiles. At the points of intersection, the metal rods must be welded or soldered. On the same fig. 9 also shows the location of the active web of the antenna with points P-P, U-U. The canvas is removed from the flat reflector - the bottom of the truncated horn - by 128 mm. The arrow symbolizes the orientation of the vector E. Almost all projections of the reflector rods on the frontal plane are parallel to the vector E. The only exceptions are some of the power rods that form the reflector frame. If the reflector is made of tubes, the diameter of the tubes of the power rods can be 12 ... 14 mm, and the rest - 4 ... 5 mm.
The directivity factor of an antenna with a reflector of the "truncated horn" type, with given dimensions, is comparable with the directivity factor of a three-dimensional rhombus (1) and varies over the frequency range within 40 ... 65. This means that at the upper frequencies of the operating range of the antenna, half the opening angle of its radiation pattern is about 17°.
The shape of the antenna pattern shown in fig. 9 is approximately the same for both planes of polarization. When installing the antenna on the ground, it is oriented to the television center. The design of the antenna is axisymmetric with respect to the direction to the television center, which can become a source of polarization error when it is mounted on a mast. Here it is necessary to take into account what polarization the signals coming from the television center have. With their horizontal polarization, the feed points a-b of the antenna should be located in the horizontal plane, and with vertical polarization - in the vertical plane.
Literature
Kharchenko K., Kanaev K. Volumetric rhombic antenna. Radio, 1979, No. 11, p. 35-36.
Antenna Kharchenko
- The zigzag antenna, proposed by K. P. Kharchenko in the 60s, is very popular with radio amateurs due to its simple design, good repeatability and broadband.
Within the frequency range for which the antenna is designed, it has constant parameters and practically does not require tuning.
It is an in-phase antenna array of two diamond-shaped elements located one above the other and having one common pair of feed points.
A zigzag antenna is most often used as a broadband antenna for receiving television programs in the ranges of 1 - 5, 6 - 12 or 21 - 60 UHF channels.
It can also be successfully used to work in amateur VHF bands by making
its for 145 MHz or for 433 MHz. A zigzag antenna with a reflector has a one-sided radiation pattern in the form of elongated ellipses both in the horizontal and vertical planes, and the rear lobe is practically absent.
With the seeming bulkiness of the entire system at first glance (Yags require much less and less consumption of materials), this system completely covers the range of 144-148 MHz (in fact, the band is much wider, about 12 MHz) with a good SWR not exceeding 1.2-1.3 and has the best radiation pattern. The gain of such an antenna is about 8.5 DBd, which is equivalent to about 4el YAGI at 145 MHz. A system of two such antennas already develops about 15 DBd. It has a more pressed radiation lobe, maximally adapted for conducting radio communications in the VHF bands. Antenna powered by a 50 ohm cable.
I made an antenna and improvised material in a literal sense. There was a sheet of galvanized sheet 0.8 mm thick from which I cut all the strips into antenna elements, and a couple of wooden slats. The fastening of the strips is made using a conventional riveter for 3-4 rivets in the corners. The width of all bands is about 40 mm, which provided a greater broadband for this antenna. The reflector strips are screwed to a wooden carrier (pre-painted) with ordinary screws.
- For the 145 MHz band, the dimensions are as follows:
The reflector has a length of 1050mm x 40mm for each strip.
Frame side 510mm.
The gap between the corners of the frames at the cable connection point - 40mm
Distance between active element and reflector - 300mm
The whole structure is visible and understandable from the photographs.
- The antenna can also be performed on the TV range.
Set it to horizontal or vertical polarization.
Below, the table for TV frequency channels is shown
Horizontal polarization
Vertical polarization
Antenna Kharchenko
or how it looks in nature :))
Resonance frequency 145.0 MHz
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| Pic 1 Fastening elements |
Pic 2 Antenna reflector |
Pic 3 zigzag element |
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| Pic 4 Power point |
Pic 5 carrier mount to the mast |
Pic 6 Racks and insulator in the center |
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| Pic 7 3 el.YAGI 145 mhz (for example) |
Pic 8 All is ready to installation |
Pic 9 Worth a beauty! |
ON-LINE calculator, for calculation
Kharchenko's antennas
Note: D - distance between antenna and reflector
Antenna Kharchenko
for low frequency range DCMA - 450-460 MHZ
Resonance frequency 452.0 MHz
- The antenna was made from improvised materials. Used old reflector grid
from the Polish VHF-TV antenna, which, due to its unsuitability, was already simply thrown away by me.
As an active element, I used an aluminum wire from an electric cable with a diameter of 4.5mm. The cable used is thin, RG-58/C, 50 ohm, 3 meters long. All calculations are based on the data of the online calculator. The difference in signal strength, according to the built-in
in the modem to the field meter, compared to the standard tail antenna, was more than 20db, that is, the readings with the standard antenna never dropped below -95db on the EvDO signal.
When the Kharchenko antenna was connected, the signal increased and is now at -72db and sometimes even up to -70db. The base station is 10 km away from the reception point. Due to its broadband, the antenna does not need to be tuned.
Thus, if you put a cable with low linear attenuation at these frequencies, install an antenna at a height of more than 15 m from the ground, you can easily block the distance to the DCMA BASE of more than 20-25 km and get access to the Internet, even in a very remote village))) )
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| Pic 1 Antenna ready to installation |
Pic 2 Set at level 2 floors |
Pic 3 View of the antenna out of the window |
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| Pic 4 AXESS-TEL modem CDMA 1-EvDO |
Pic 5 S-meter readings modem |
Under the abbreviation UHF, we mean decimeter waves that are in the range from 10 centimeters to one meter. It is in this range that some TV channels broadcast, and they are picked up by decorating the roof of every house.
Antenna Requirements
In the event of a breakdown of this device or a poor signal level, you can resort to using a do-it-yourself UHF antenna assembled from materials that are at hand in many homes in the country.
A device for capturing decimeter waves can be external and internal, differ in assembly features, as well as characteristics. The best signal reception, of course, is carried out by the external type.
Such a device can be lifted to the roof, although an indoor device is sometimes comparable to a standard outdoor antenna.
Everything else depends on the immediate place of residence of the user, since UHF are distributed over short distances.
So, signal strength is lost with every kilometer, so a home-made antenna made by one's own hands can only help if there is at least a theoretical possibility of reaching a signal from the user's tower.
Types of antennas and assembly features
Important points should be considered when making this device with your own hands. Each of the varieties has its own assembly features, described below.
DIY zigzag type
In this video, you will be told how you can make a very simple zigzag antenna with your own hands.
The positive quality of the zigzag variety is a wide field for experimenting with material and dimensions.
The design allows for the possible introduction of its own changes to it within a fairly wide range, while continuing its work, allowing improvements to be made.
The assembly of this device is quite simple and does not require special skills. Looking at the assembled device, it becomes clear that such a design can be improved by creating additional screens or by changing the width and number of slats.
The antenna reflector may well be assembled from strips of metal or from metal tubes. Racks must be made of dielectric.
The reflector does not "lie" on the canvas, it is separated from it at a short distance due to the use of racks. The distance between the grid conductors should be no more than one centimeter.
Simple room type
An example of a homemade indoor antenna
The convenience of an indoor antenna lies in the fact that it is possible to instantly adjust it.
One has only to rearrange it from place to place, or turn it around its axis, observing the change in signal quality.
Still, it is not affected by the wind, as well as precipitation and other environmental conditions.
The indoor variety can be made in several ways. The simplest is made using coaxial cable and materials handy to give it the desired shape.
An open ring is twisted from a 530 mm cut, to which a cable is connected leading directly to the TV. The second cut of 175 mm is bent in the form of a loop, which is connected to the ends of the first cable, there should be a distance of 20-30 millimeters between them.
Using a plywood board with a central hole in it, the resulting structure is installed on any flat surface. So, it turns out an UHF antenna made of coaxial cable. It is not very powerful, but it can be easily crafted and also disassembled for rework.
DIY loop antenna
It has a high gain and can be used both indoors and outdoors. It is distinguished by ease of manufacture, availability of materials, small size, aesthetic appearance.
For manufacturing, a wire is taken from copper, steel, brass, aluminum with a diameter of 3-8 mm and bends. At the joints, the wires must be soldered.
The antenna cable is soldered, and the cable sheath must be connected to the material of the entire device.
log-periodic type
Type of log-periodic UHF antenna
This is a broadband terrestrial antenna that provides reception of broadcasts from multi-program television centers with various combinations of channels.
The working band from the side of the lower frequencies is limited by the dimensions of the larger vibrator of the device.
And from the upper side - the size of a smaller vibrator.
It will take a little time to make this variety for digital television, and the reception quality is high.
It turns out to be very simple and reliable, and the reception of digital television is confident.
The dimensions of the elements, as well as the option of connecting the cable, were worked out experimentally.
Television signals have been received for several years.
The design of the log-periodic type is a two-wire symmetrical distribution line made of 2 identical pipes arranged in parallel.
7 semi-vibrators are fixed on each of them.
Each subsequent semi-vibrator is directed in the opposite direction with respect to the previous one.
The planes, at the same time, are parallel, and the semi-vibrators on different pipes are directed in opposite directions.
The coaxial cable runs inside one of the pipes, with the ends of the pipes connected by a metal plate.
In the place where the cable exits to give rigidity to the structure, a dielectric bar is installed.
The cable sheath is soldered when the cable exits the pipe, and the central conductor is soldered to the lug, which is fixed to the plugged end of the second pipe.
Does not need setting.
Do-it-yourself simple UHF antenna
An example of a simple homemade antenna
A homemade antenna allows you to conduct fairly confident reception of television broadcasting signals in the decimeter range.
The antenna is intended for outdoor installation.
The design is 2 nested "eights", bent from a separate piece of wire.
The connection of the wire to obtain the shape of the structure, similar to the "eight", is made in the place of the central bend.
The ends of the wire are connected by soldering.
All connections of the antenna structure are soldered, which provides good electrical contact, which reduces the noise of the device.
For reliable fastening and certainty of electrical contact, the ends of the wire before soldering should be cleaned with sandpaper, degreased with an acetone-based solvent, and tightened with copper wire of only a smaller diameter.
Using a soldering iron does not allow you to perform high-quality soldering. Instead of using a soldering iron, the soldering area is heated over the burner of a gas stove with the addition of rosin. A small piece of wire is soldered to the inner "eight" in the fold in order to connect the cable screen.
The connection of two "eights" is made by soldering and thin copper wire, while the inner "eight" is displaced inside the outer one. Two eights are in the same plane.
Further, on the connected "eights" it is necessary to install two plastic horizontal crossbars, which reinforce the structure and align the position of the elements in the same plane. The plates are fastened with the help of turns of a PVC insulating tube.
From 2 cans (0.5 l) you can get a completely worthy replacement for the purchased antenna.
But there is also a minus: such a device only works in the UHF range. To achieve more channels, you will need two liter jars.
The central core is soldered to one bank - a signal, to the other - a shielded braid. Then they are attached with adhesive tape to the hanger (its lower part).
On the reverse side, you need to remove the antenna plug. To get a decent view, you need to adjust the distance between the banks. So you can make the simplest homemade antenna.
Let's figure out how to do it this device, with the least losses and costs. The main pipe, like all other parts, should be selected from brass, copper or aluminum. Their surface should not be rough.
An antenna made of steel will be heavy, and signal reception is not of high quality. In addition, it will rust, as it is supposed to be mounted on the street. The main tube should be two meters long.
On it with screws with a diameter of 5 mm, tubes of a smaller diameter are fastened with a distance between them of 30 cm.
Assembly requires a drill and a drill. The length of the subsequent tube should be 10 cm shorter. Opposite the largest tube, a reflector is attached in the form of a structure of three tubes connected in parallel. Then the vibrator is mounted on the pipe.
It is not clear to many how to make a catcher for decimeter waves so that it has an aesthetic appearance, is not bulky and accepts all available channels. There is a way out - this is an antenna with a loop vibrator. After assembling the device, solder the loop.
A piece of special wire 60 cm is taken, the ends are stripped so that the braid is connected together, and attached to the main tube. Central wires - to the vibrator.
Connections must be well sealed to avoid moisture ingress. The vibrator is a loop made of the same material as the entire device.
The distance between the ends of the vibrator is 10 cm, the central wires are connected to them. Then the antenna wire is connected with a plug of the required length.
Usually this option is set higher. It is better to use a wooden block 50x50 mm, 6 meters long. It is necessary to fix the antenna on it, having previously distributed the wire along the entire length and install this structure on the roof of the house.
Let's review the origins: the biquadrat is considered a subspecies of loop antennas, which first of all belong to the zigzag genus. Kharchenko K.P. Kharchenko was the first to offer the antenna. In 1961 to catch TV shows. It is known for certain: at a frequency of 14 MHz, having put a biquadrate in a meadow, an ardent enthusiast managed to get America. Not a bad result. We believe that the matter affects refraction, plus diffraction beats the Earth. HF range, and below, are used due to the ability of waves to refract, bend around obstacles, it is possible to establish communication on long distance. Let's go in order. Let's see in detail how the Kharchenko antenna is made with our own hands.
Antenna Kharchenko, "eight", which today catches WiFi, cellular 3G. For outdoor installation, protect the product with a plastic housing.
Communications and antennas Kharchenko
Later it will become obvious: the device of Kharchenko's original antenna, to put it mildly, differs from that observed today on the network. It’s not that they liked, as Mayakovsky used to say, to delve into the prehistoric city ...., but the basics of the theory must be studied in order to avoid mistakes, to know the features of the design. We are going to tell you how to make the Kharchenko antenna yourself. The author of the monograph avoids giving instructions on the choice of wire thickness, saying that reducing the diameter negatively affects the range. Kharchenko's self-made antenna is capable of covering digital television of the 470 - 900 MHz spectrum. The characteristics of the device are amazing, matching is not very difficult. We will tell you how to make a Kharchenko antenna, avoiding delving into theory. Miners are advised to study the original thematic edition of the author.
The length of the 14 MHz frequency biquad wire is approximately 21 meters. So many cable-voles will be needed to make a simple device. The device is powered by a television coaxial wire (wave impedance 75 ohms). Eyewitnesses are sure: Kharchenko's antenna tuning is not required. The authors tend to consider the latter a slight (giant size) exaggeration. Think about it! You can surf the natural landscape with two coils of wire on your back:
- a skein of a vole;
- coil of coaxial television cable.
Then deploy the antenna, the range of which is simply amazing. Polarization depends on which side to turn the figure eight. Let's reluctantly place it, as the numeral icon is written in arithmetic textbooks - we will begin to receive television, we will fill it up on its side, forming infinity - broadcasting will begin to be caught. Since the vole bends well, unbends back: we don’t like one channel, we can quickly orient the antenna to another. The problem is disgusting: the extra wire, which is redundant for useful needs, will either have to be cut or wound in a bay, placed so that it does not interfere with reception. And this is not such a trivial task as it seems to the first comer:
- put it horizontally - it will catch television;
- if you stretch it to the ground, the intermediate wire will take on vertical polarization;
- hang it on a bough - vertical polarization will be caught.
Kharchenko antenna design
I'm used to seeing the same things in pictures. Here is how it is proposed to design the Kharchenko antenna (VashTechnik portal keeps pace):
- It is necessary to find out the frequency of the wave, polarization. Antenna Kharchenko friendly linear.
- The copper antenna is formed by two squares. Both stand at the corners, one touches. For horizontal polarization, the figure eight stands upright; vertical - lays on its side.
- The side of the square is found by the formula: wavelength divided by four.
- One can imagine the construction if one imagines an oval contracted in the center across the larger side. The sides do not touch, although they are close to each other.
- The power cable is connected to the points of convergence of the sides. It is necessary to block one direction of the diagram - a flat copper screen is placed at a distance of 0.175 of the working wavelength, it sits on the braid of the power cable. The reflector is made of a metal plate. In the old days, textolite boards coated with copper were used.
Completed brief design of the Kharchenko antenna. Details are overgrown with problems: the task is to strengthen the emitter. For communication range - wire extensions; television - a wooden frame is often used, humiliated by crossbars (resembling a cross), in the microwave range, modem owners support the emitter with a pair of plastic racks penetrating the screen. What does Kharchenko think about design concepts. The obedient slaves of the VashTechnik portal took the trouble to get a book authored by an engineer, the text outlines the invention, a mountain of interesting things is written:
The geometric dimensions are indicated, we list together:
- The height of the square standing on the corner is 0.28 of the maximum wavelength, along the middle contour of the three.
- The distance between the extreme frames across the direction of the wire is 0.033 of the maximum wavelength.
- The length of the matching line with a wave impedance of 100 ohms is 0.052 or 0.139 of the maximum wavelength.
What else I would like to note from the original design ... In order not to disturb the field of Kharchenko's antenna, the power cable comes from below, winds along one side of the frame, goes into the center. The vein does not go along the mast! Modern designs imply the presence of a screen. Therefore, the wire comes from somewhere behind, breaks through the copper screen, connects to right place to eight. It is not at all necessary, by the way, that the antenna consists of squares. The characteristics of the device do not strongly depend on the angle at the top. The height of the eight (standing upright) must be maintained. Therefore, if the angle changes from 90 to 120 degrees, the sides lengthen. proportionally. You can calculate specific values.
Now readers know how the Kharchenko antenna was made with their own hands. And here's something else. It was possible to see, surfing the net, constructions where the emitter was bent around the screen. Thus, the main lobe of the radiation pattern supposedly expands. In practice, in this case it is easier to use a patch. Here the platforms can be directed in different directions.
once good TV antenna was in short supply, purchased quality and durability, to put it mildly, did not differ. Making an antenna for a “box” or “coffin” (an old tube TV) with your own hands was considered an indicator of skill. Interest in homemade antennas does not fade away even today. There is nothing strange here: TV reception conditions have changed dramatically, and manufacturers, believing that there is nothing essentially new in the theory of antennas and there will not be, most often adapt electronics to well-known designs, without thinking about the fact that The main thing for any antenna is its interaction with the signal on the air.
What has changed on the air?
Firstly, almost the entire volume of TV broadcasting is currently carried out in the UHF band. First of all, for economic reasons, it greatly simplifies and reduces the cost of the antenna-feeder economy of transmitting stations, and, more importantly, the need for its regular maintenance by highly qualified specialists engaged in hard, harmful and dangerous work.
Second - TV transmitters now cover almost all more or less populated places with their signal, and a developed communication network ensures the delivery of programs to the most remote corners. There, broadcasting in the habitable zone is provided by low-power, unattended transmitters.
Third, the conditions for the propagation of radio waves in cities have changed. On the UHF, industrial interference leaks weakly, but reinforced concrete high-rise buildings for them are good mirrors, repeatedly reflecting the signal until it is completely attenuated in the zone of seemingly confident reception.
Fourth - There are a lot of TV programs on the air now, dozens and hundreds. How diverse and meaningful this set is is another question, but it is now meaningless to count on receiving 1-2-3 channels.
Finally, development of digital broadcasting. The DVB T2 signal is something special. Where it still exceeds the noise even a little, by 1.5-2 dB, the reception is excellent, as if nothing had happened. And a little further or to the side - no, as cut off. The "digit" is almost insensitive to interference, but if there is a mismatch with the cable or phase distortions anywhere in the path, from the camera to the tuner, the picture can crumble into squares even with a strong clean signal.
Antenna Requirements
In accordance with the new reception conditions, the basic requirements for TV antennas have also changed:
- Its parameters such as directivity coefficient (DAC) and protective action coefficient (CPA) do not have a decisive value now: modern ether is very dirty, and along the tiny side lobe of the directivity pattern (DN), at least some kind of interference, yes it will crawl through, and it is necessary to deal with it by means of electronics.
- Instead, the intrinsic gain of the antenna (KU) is of particular importance. An antenna that “catches” the air well, and does not look at it through a small hole, will provide a power reserve for the received signal, allowing the electronics to clear it of noise and interference.
- A modern television antenna, with rare exceptions, must be a band antenna, i.e. her electrical parameters should be preserved in a natural way, at the level of theory, and not squeezed into an acceptable framework by engineering tricks.
- The TV antenna must be coordinated in the cable over its entire operating frequency range without additional devices matching and balancing (USS).
- The frequency response of the antenna (AFC) should be as smooth as possible. Sharp surges and dips are inevitably accompanied by phase distortions.
The last 3 points are due to the requirements for receiving digital signals. Customized, i.e. operating theoretically at the same frequency, antennas can be "stretched" in frequency, for example. antennas of the "wave channel" type on the UHF with an acceptable signal-to-noise ratio capture channels 21-40. But their coordination with the feeder requires the use of OSS, which either strongly absorb the signal (ferrite), or spoil the phase response at the edges of the range (tuned). And such an antenna, which works perfectly on an “analog”, will receive a “digit” badly.
In this regard, from all the great antenna variety, this article will consider TV antennas available for self-manufacturing of the following types:
Note: The Z-antenna, to use the previous analogy, is a frequent nonsense, raking up everything that is in the water. As the air became littered, it fell out of use, but with the development of digital TV, it again found itself on a horse - in its entire range it is just as perfectly coordinated and keeps the parameters as a “speech therapist”.
Precise matching and balancing of almost all the antennas described below is achieved by laying the cable through the so-called. point of zero potential. It has special requirements, which will be discussed in more detail below.
About vibrator antennas
Up to several tens of digital channels can be transmitted in the frequency band of one analog channel. And, as already mentioned, the figure works with an insignificant signal-to-noise ratio. Therefore, in places very remote from the television center, where the signal of one or two channels barely finishes, for receiving digital TV, the good old wave channel (AVK, wave channel antenna), from the class of vibrator antennas, can also be used, so at the end we will devote a few lines and to her.
About satellite reception
do it yourself satellite dish there is no point. You still need to buy a head and a tuner, and behind the external simplicity of the mirror lies a parabolic oblique incidence surface, which not every industrial enterprise can perform with the required accuracy. The only thing that DIYers can do is set up a satellite dish, read about it here.
About antenna parameters
The exact determination of the antenna parameters mentioned above requires knowledge of higher mathematics and electrodynamics, but it is necessary to understand their meaning when starting to manufacture an antenna. Therefore, we give a somewhat rough, but still clarifying definition (see the figure on the right):
To determine the parameters of antennas
- KU - the ratio of the signal power received by the antenna to the main (main) lobe of its DN, to its same power, received in the same place and at the same frequency, omnidirectional, with a circular, DN, antenna.
- KND is the ratio of the solid angle of the entire sphere to the solid angle of the opening of the main lobe of the RP, assuming that its cross section is a circle. If the main lobe has different sizes in different planes, you need to compare the area of the sphere and the cross-sectional area of \u200b\u200bthe main lobe.
- CPD is the ratio of the signal power received to the main lobe to the sum of the interference powers at the same frequency received by all side (back and side) lobes.
Notes:
It should be remembered that KU and KND are not necessarily interconnected. There are antennas (for example, "spy" - a single-wire traveling wave antenna, ABC) with high directivity, but unity or less gain. Such look into the distance as if through a diopter sight. On the other hand, there are antennas, eg. Z-antenna, in which low directivity is combined with significant gain.
About the intricacies of manufacturing
All elements of the antennas, through which the currents of the useful signal flow (specifically, in the descriptions of individual antennas), must be interconnected by soldering or welding. In any prefabricated assembly in the open air, electrical contact will soon be broken, and the parameters of the antenna will deteriorate sharply, up to its complete uselessness.
This is especially true for points of zero potential. In them, as experts say, there is a voltage node and current antinode, i.e. his highest value. Current at zero voltage? Nothing surprising. Electrodynamics has gone as far from Ohm's law on direct current as the T-50 has gone from a kite.
Places with zero potential points for digital antennas are best made from bent solid metal. A small "creeping" current in welding when receiving an analogue in the picture, most likely, will not affect. But, if a figure is received at the noise boundary, then the tuner may not see the signal due to the “creep”. Which, with a pure current in the antinode, would give a stable reception.
About cable soldering
The braid (and often the central core) of modern coaxial cables are not made of copper, but of corrosion-resistant and inexpensive alloys. They solder poorly and if you heat for a long time, you can burn the cable. Therefore, you need to solder cables with a 40-watt soldering iron, low-melting solder and with flux paste instead of rosin or alcohol rosin. There is no need to spare the paste, the solder immediately spreads along the veins of the braid only under a layer of boiling flux.
Frequency independent antenna with horizontal polarization
Types of antennas
All-wave
An all-wave (more precisely, frequency-independent, CNA) antenna is shown in fig. She is two triangular metal plates, two wooden slats, and a lot of copper enameled wires. The diameter of the wire does not matter, and the distance between the ends of the wires on the rails is 20-30 mm. The gap between the plates to which the other ends of the wires are soldered is 10 mm.
Note: instead of two metal plates, it is better to take a square of one-sided foil fiberglass in triangles cut out on copper.
The width of the antenna is equal to its height, the opening angle of the canvases is 90 degrees. The cable laying diagram is shown in the same place in Fig. The point marked in yellow is the point of quasi-zero potential. It is not necessary to solder the cable sheath to the web in it, it is enough to tie it tightly, for coordination there will be enough capacity between the braid and the web.
CNA, stretched in a window 1.5 m wide, receives all meter and DCM channels from almost all directions, except for a dip of about 15 degrees in the canvas plane. This is its advantage in places where it is possible to receive signals from different television centers, it does not need to be rotated. Disadvantages - a single KU and zero KZD, therefore, in the zone of interference and outside the zone of reliable reception, the CHNA is not suitable.
Note: There are other types of NNA, for example. in the form of a two-turn logarithmic spiral. It is more compact than triangular canvases in the same frequency range, therefore it is sometimes used in technology. But in everyday life this does not give advantages, it is more difficult to make a spiral CNA, it is more difficult to coordinate with a coaxial cable, therefore we do not consider it.
Based on the CNA, a once very popular fan vibrator (horns, flyer, slingshot) was created, see fig. Its directivity and efficiency are something around 1.4 with a fairly smooth frequency response and linear phase response, so it would be suitable for digital even now. But - it works only on MV (1-12 channels), and digital broadcasting going to DMV. However, in the countryside, when climbing 10-12 m, it can be suitable for receiving an analogue. The mast 2 can be made of any material, but the mounting straps 1 are made of a good non-wetting dielectric: fiberglass or fluoroplast with a thickness of at least 10 mm.
Fan vibrator for MV TV reception
Beer all-wave
beer can antennas
The all-wave antenna made of beer cans is clearly not the fruit of the hangover hallucinations of a drunken radio amateur. This is really a very good antenna for all reception cases, you just need to make it right. And extremely simple.
Its design is based on the following phenomenon: if you increase the diameter of the arms of a conventional linear vibrator, then its operating frequency band expands, while other parameters remain unchanged. Since the 1920s, long-distance radio communications have been using the so-called. Nadenenko dipole based on this principle. And beer cans are just right in size as the arms of a vibrator on the UHF. In essence, the PNA is a dipole, the arms of which expand indefinitely to infinity.
The simplest beer vibrator of two cans is suitable for indoor reception of an analogue in the city, even without coordination with the cable, if its length is not more than 2 m, on the left in fig. And if you assemble a vertical in-phase array from beer dipoles with a step of half a wave (on the right in the figure), match it and balance it with an amplifier from a Polish antenna (we will talk about it later), then due to the vertical compression of the main lobe of the DN, such an antenna will give and good ku.
The gain of the "pivnukha" can be further increased by adding at the same time a KZD, if a screen from the grid is placed behind it at a distance equal to half the lattice spacing. A beer grate is mounted on a dielectric mast; mechanical connections of the shield with the mast are also dielectric. The rest is clear from the next. rice.
In-phase array of beer dipoles
Note: the optimal number of lattice floors is 3-4. With 2, the gain in gain will be small, and more difficult to match with the cable.
Video: antenna from beer cans in the program "Cheap and cheerful"
"Speech therapist"
A log-periodic antenna (LPA) is a collecting line to which halves of linear dipoles (i.e., pieces of a conductor a quarter of the working wavelength) are alternately connected, the length and distance between which change exponentially with an exponent less than 1, in the center in Fig. The line can be either configured (with a short circuit at the end opposite the cable connection point) or free. An LPA on a free (unconfigured) line is preferable for receiving a digit: it comes out longer, but its frequency response and phase response are smooth, and matching with the cable does not depend on frequency, so we will stop at it.
Design of a log-periodic antenna
LPA can be manufactured for any, up to 1-2 GHz, predetermined frequency range. When the operating frequency changes, its active region of 1-5 dipoles shifts back and forth along the canvas. Therefore, the closer the progression indicator is to 1, and, accordingly, the smaller the antenna opening angle, the greater the gain it will give, but at the same time its length increases. On the UHF, 26 dB can be achieved from an external LPA, and 12 dB from a room one.
LPA, we can say, in terms of the combination of qualities, an ideal digital antenna, so let's dwell on its calculation in more detail. The main thing to know is that an increase in the progression rate (tau in the figure) gives an increase in gain, and a decrease in the opening angle of the LPA (alpha) increases directivity. The screen for the LPA is not needed, it has almost no effect on its parameters.
The calculation of a digital LPA has the following features:
Let's explain with an example. Let's say our digital programs lie in the range of 21-31 TVK, i.e. at 470-558 MHz in frequency; wavelengths, respectively - 638-537 mm. Let's also assume that we need to receive a weak noisy signal far from the station, so we take the maximum (0.9) progression indicator and the minimum (30 degrees) opening angle. For the calculation, you need half the opening angle, i.e. 15 degrees in our case. Opening can be further reduced, but the length of the antenna will increase exorbitantly, in terms of cotangent.
We consider B2 in Fig: 638/2 = 319 mm, and the dipole arms will be 160 mm each, you can round up to 1 mm. The calculation will need to be carried out until Bn = 537/2 = 269 mm is obtained, and then another dipole is calculated.
Now we consider A2 as B2 / tg15 \u003d 319 / 0.26795 \u003d 1190 mm. Then, through the progression indicator, A1 and B1: A1 = A2 / 0.9 = 1322 mm; B1 \u003d 319 / 0.9 \u003d 354.5 \u003d 355 mm. Then sequentially, starting with B2 and A2, we multiply by the indicator until we reach 269 mm:
- B3 \u003d B2 * 0.9 \u003d 287 mm; A3 \u003d A2 * 0.9 \u003d 1071 mm.
- H4 = 258 mm; A4 = 964 mm.
Stop, we already have less than 269 mm. We check whether we meet the gain, although it’s already clear that we don’t: in order to get 12 dB or more, the distances between the dipoles should not exceed 0.1-0.12 wavelengths. In this case, we have for B1 A1-A2 \u003d 1322 - 1190 \u003d 132 mm, and this is 132/638 \u003d 0.21 of the wavelength of B1. It is necessary to “pull up” the indicator to 1, to 0.93-0.97, so we try different ones until the first difference A1-A2 is halved or more. For a maximum of 26 dB, you need a distance between dipoles of 0.03-0.05 wavelengths, but not less than 2 dipole diameters, 3-10 mm on UHF.
Note: the rest of the line behind the shortest dipole, we cut it off, it is needed only for calculation. Therefore, the actual length of the finished antenna will be only about 400 mm. If our LPA is outdoor, this is very good: you can reduce the opening, getting more directivity and protection from interference.
Video: DVB T2 Digital TV Antenna
About line and mast
The diameter of the tubes of the LPA line on the DMV is 8-15 mm; the distance between their axes is 3-4 diameters. We also take into account that thin “lace-up” cables give such attenuation per meter to the UHF that all antenna-amplifying tricks will come to naught. The coaxial for the external antenna must be taken good, with a shell diameter of 6-8 mm. That is, the tubes for the line must be thin-walled seamless. It is impossible to tie the cable to the line from the outside, the quality of the LPA will drop sharply.
It is necessary, of course, to fasten the outer LPA to the mast by the center of gravity, otherwise the low windage of the LPA will turn into a huge and shaking one. But it is also impossible to connect a metal mast directly to the line: it is necessary to provide a dielectric insert at least 1.5 m long. The quality of the dielectric does not play a big role here, the oiled and painted wood will do.
About the Delta Antenna
If the UHF LPA is consistent with the amplifier cable (see below, about Polish antennas), then the shoulders of a meter dipole, linear or fan-shaped, can be attached to the line, like a "slingshot". Then we get a universal MV-UHF antenna of excellent quality. This solution is used in the popular Delta antenna, see fig.
Antenna "Delta"
Zigzag on air
The Z-antenna with a reflector gives the same gain and QPV as the LPA, but its main lobe is more than twice as wide horizontally. This may be important in the countryside, when there is TV reception from different directions. And the decimeter Z-antenna has small dimensions, which is essential for indoor reception. But its operating range is theoretically not unlimited, frequency overlap while maintaining parameters acceptable for digital - up to 2.7.
Z-antenna MV
The design of the MV Z-antenna is shown in Figure; the cable path is highlighted in red. In the same place at the bottom left - a more compact ring version, colloquially - a "spider". It clearly shows that the Z-antenna was born as a combination of a CNA with a range vibrator; there is something in it from a rhombic antenna, which does not fit into the topic. Yes, the spider ring does not have to be wooden, it can be a metal hoop. "Spider" receives 1-12 MV channels; DN without a reflector is almost circular.
The classic zigzag works either on 1-5 or 6-12 channels, but for its manufacture you only need wooden slats, enameled copper wire c d = 0.6-1.2 mm and a few scraps of foil fiberglass, so we give dimensions, through shot for 1-5/6-12 channels: A = 3400/950 mm, B, C = 1700/450 mm, b = 100/28 mm, B = 300/100 mm. At point E - zero potential, here you need to solder the braid with a metallized base plate. The reflector dimensions are also 1-5/6-12: A = 620/175 mm, B = 300/130 mm, D = 3200/900 mm.
A range Z-antenna with a reflector gives a gain of 12 dB, tuned to one channel - 26 dB. In order to build a single-channel zigzag based on a range zigzag, you need to take the side of the square of the canvas in the middle of its width to a quarter of the wavelength and recalculate proportionally all other dimensions.
folk zigzag
As you can see, the MV Z-antenna is a rather complex structure. But its principle shows itself in all its splendor in the DMV. The UHF Z-antenna with capacitive inserts, which combines the advantages of "classics" and "spider", is so easy to make that it earned the title of people's in the USSR, see fig.
People's UHF antenna
Material - copper tube or aluminum sheet with a thickness of 6 mm. The side squares are solid metal or covered with a mesh, or closed with a tin. In the last two cases, they need to be soldered along the contour. The coax cannot be bent sharply, so we guide it so that it reaches the side corner, and then does not go beyond the capacitive insert (side square). At point A (zero potential point), we electrically connect the cable sheath to the web.
Note: aluminum is not soldered with conventional solders and fluxes, therefore aluminum "folk" is suitable for outdoor installation only after sealing electrical connections silicone, because everything is on the screws.
Video: Dual Delta Antenna Example
wave channel 
Antenna wave channel
The wave channel antenna (AVK), or the Udo-Yagi antenna available for self-production, is capable of giving the highest KU, KND and KZD. But it can receive a figure on the UHF only on 1 or 2-3 adjacent channels, tk. belongs to the class of sharply tuned antennas. Its parameters outside the tuning frequency deteriorate sharply. VKA is recommended to be used with very poor reception conditions, and for each TVK, make a separate one. Luckily, it's not very difficult - AVK is simple and cheap.
At the heart of the work of the AVC is the "raking" of the electromagnetic field (EMF) of the signal to the active vibrator. Outwardly small, light, with minimal windage, AVK can have an effective aperture of tens of wavelengths of operating frequency. Shortened and therefore having a capacitive impedance (impedance) directors (directors) direct the EMF to the active vibrator, and the reflector (reflector), elongated, with an inductive impedance, throws back to it what slipped past. Only 1 reflector is needed in AVK, but there can be from 1 to 20 or more directors. The more of them, the higher the amplification of the AVC, but the narrower its frequency band.
From the interaction with the reflector and directors, the wave impedance of the active (from which the signal is taken) of the vibrator drops the more, the closer the antenna is tuned to the maximum gain, and coordination with the cable is lost. Therefore, the active dipole AVK is made loop, its initial impedance is not 73 ohms, as in a linear one, but 300 ohms. At the cost of reducing it to 75 ohms, an AVC with three directors (five-element, see the figure on the right) can be tuned to almost a maximum gain of 26 dB. Characteristic for AVC RP in the horizontal plane is shown in fig. at the beginning of the article.
AVK elements are connected to the boom at zero potential points, so the mast and boom can be anything. Polypropylene pipes work very well.
The calculation and setting of AVK for analog and digital are somewhat different. For an analogue, the wave channel must be calculated for the carrier frequency of the image F and for a digital one, for the middle of the TVK spectrum Fc. Why so - here to explain, unfortunately, there is no place. For the 21st TVK Fi = 471.25 MHz; Fc = 474 MHz. UHF TVK are located close to each other through 8 MHz, so their tuning frequencies for AVC are calculated simply: Fn = Fi / Fc (21 TVK) + 8 (N - 21), where N is the number of the desired channel. Eg. for 39 TVK Fi = 615.25 MHz, and Fc = 610 MHz.
In order not to write down a lot of numbers, it is convenient to express the dimensions of the AVC in fractions of the operating wavelength (it is considered as L \u003d 300 / F, MHz). The wavelength is usually denoted by the small Greek letter lambda, but since there is no Greek alphabet by default on the Internet, we will conditionally denote it with a large Russian letter L.
The dimensions of the AVK optimized for the figure, according to Fig., are as follows:
U-loop: USS for AVK
- P = 0.52L.
- B \u003d 0.49L.
- D1 = 0.46L.
- D2 = 0.44L.
- D3 \u003d 0.43 l.
- a = 0.18L.
- b = 0.12L.
- c \u003d d \u003d 0.1L.
If you do not need a lot of gain, but it is more important to reduce the dimensions of the AVK, then D2 and D3 can be removed. All vibrators are made of a tube or rod with a diameter of 30-40 mm for 1-5 TVK, 16-20 mm for 6-12 TVK and 10-12 mm for UHF.
AVK requires precise matching with the cable. It is the careless implementation of the matching and balancing device (USS) that explains most of the failures of amateurs. The simplest CSS for AVK is a U-loop from the same coaxial cable. Its design is clear from Fig. on right. The distance between the signal terminals 1-1 is 140 mm for 1-5 TVK, 90 mm for 6-12 TVK and 60 mm for UHF.
Theoretically, the length of the knee l should be half the length of the working wave, as it appears in most publications on the Internet. But the EMF in the U-loop is concentrated inside the cable filled with insulation, so it is necessary (for a figure, it is especially necessary) to take into account its shortening factor. For 75-ohm coaxes, it ranges from 1.41-1.51, i.e. l you need to take from 0.355 to 0.330 wavelengths, and take it exactly so that the AVC is an AVC, and not a set of pieces of iron. The exact value of the velocity factor is always on the cable certificate.
Recently, the domestic industry has begun to produce reconfigurable AVK for digital, see fig. The idea, I must say, is excellent: by moving the elements along the boom, you can fine-tune the antenna to local reception conditions. It is better, of course, for a specialist to do this - the element-by-element setting of the AVK is interdependent, and the amateur will certainly get confused.
AVK for digital TV
About "Poles" and amplifiers
For many users, Polish antennas, which previously decently received an analog, refuse to take a figure - it breaks, or even disappears altogether. The reason, I beg your pardon, is a bawdy-commercial approach to electrodynamics. It is sometimes a shame for colleagues who have made such a “miracle”: the frequency response and phase response look like either a psoriasis hedgehog, or a horse comb with broken teeth.
The only thing that is good about the "Polish women" is their amplifiers for the antenna. Actually, they do not allow these products to die ingloriously. First of all, the "bud" amplifiers are low-noise broadband. And, more importantly, with a high-impedance input. This allows, with the same strength of the EMF signal on the air, to apply several times more power to the tuner input, which makes it possible for the electronics to “tear out” the figure from the very ugly noises. In addition, due to the large input impedance, the Polish amplifier is an ideal CSS for any antenna: no matter what you connect to the input, the output is exactly 75 ohms without reflection and creep.
However, with a very poor signal, outside the zone of reliable reception, the Polish amplifier no longer pulls. Power is supplied to it via cable, and power decoupling takes away 2-3 dB of the signal-to-noise ratio, which may just not be enough for the figure to go into the very outback. Needed here good amplifier TV signal with separate power supply. It will most likely be located near the tuner, and the OSS for the antenna, if required, will have to be done separately.
UHF TV Signal Amplifier
The scheme of such an amplifier, which showed almost 100% repeatability even when performed by novice radio amateurs, is shown in Fig. Gain adjustment - potentiometer P1. Decoupling chokes L3 and L4 are standard purchased. Coils L1 and L2 are made according to the dimensions in the wiring diagram on the right. They are part of the bandpass signal filters, so small deviations in their inductance are not critical.
However, the topology (configuration) of the installation must be observed exactly! And in the same way, a metal shield is also required, separating the output circuits from the other circuit.
Where to begin?
We hope that even experienced craftsmen will find some useful information in this article. And for beginners who do not yet feel the ether, it is best to start with a beer antenna. The author of the article, by no means and by no means an amateur in this field, at one time was quite surprised: the simplest “beer house” with ferrite matching, as it turned out, and the MV takes no worse than the tested “slingshot”. And what is worth doing one and the other - see the text.
Kharchenko Konstantin Pavlovich
Born August 11, 1931 In 1950 in Leningrad he graduated with a medal from the secondary male school N 158 and entered the Military Engineering Academy of Communications named after S.M. Budyonny at the radio department. In 1955 enrolled in the head communications institute of the USSR Ministry of Defense. In December 1958 invented his first antenna, which for a long time became the basis of many means of communication of the Armed Forces of the USSR and the Warsaw Pact countries. Thanks to the magazine "Radio" (No. 3, 1961), she completely "won" the roofs of houses "throughout Great Russia" and far beyond its borders as a television (popularly "eight", "zigzag", "tambourine"). Six diplomas of the 1st degree from the magazine "Radio" and more than 40 years of cooperation. More than seven years of teaching work at LVVIUS named after the Leningrad City Council.
We bring to your attention, dear anonymous, Kharchenko's antenna, optimized for receiving digital television. Of course, it is equally suitable for both analog and digital television of any standard, which is broadcast in the UHF range. Why do we position it as a "digital" antenna. Firstly, very little time will pass and we will remember analog TV as some kind of antique, like a gramophone. And about the "second" should be told in more detail ...
Kharchenko's original antenna consists of two square frames with a perimeter of about 1λ, connected in parallel. Such an antenna has a low input impedance of about 75 ohms, which is very convenient for direct matching with a 75 ohm feeder, and for balancing, it is usually enough to lay this cable along one of the arms of the frame. Kharchenko's 50 ohm antenna is also great for amateur bands 144/433/1296 MHz, for CDMA-800, GSM-900, GSM-1800, WiFi-2400, which is covered on our website and a couple of online calculators. Let us draw your attention to the fact that TV broadcasting in 1961 was carried out on meter waves and the antenna bandwidth was quite enough to receive 1-2 channels, which were limited to broadcasting at that time. Gradually, television began to occupy the UHF range. The bandwidth of the Kharchenko antenna in this case was not enough. 
To solve this problem, more broadband options were proposed for analog TV, which was broadcast in the range of 470-622 MHz (21-39 frequency channels). One of the home-made versions of such an antenna, although not very successful, is shown in the figure. Currently, according to the OIRT standard, a range of 470-860 MHz (21-69 channels) is allocated for digital television. At the same time, digital multiplexes are often scattered over the entire range, and relatively narrow-band antennas are not suitable in this case, except perhaps only for receiving one of the multiplexes. To cover such a wide range, other versions of the Kharchenko antenna can be used, which have a higher input impedance. For example, rhombic double loops with a perimeter of one of the loops of about 1.5λ have an input impedance of about 300 ohms, which makes the antenna more broadband and easy to match with 300/75 ohm matching devices or antenna amplifiers that are currently widely used on the market. It was this antenna that was developed by the user under the nickname yurik82
through digital optimization in NEC2 and subsequent verification in the Ansys HFSS program (details at the end of the article). You can download archive with 4NEC2 and HFSS models for detailed study. 
The antenna is completely symmetrical both along the vertical and horizontal axes passing through the center of the antenna. All dimensions are from the center to the center of the wire, i.e. along the axes of the wires. The distance to the reflector is measured from the plane on which the axes of the wires of the frame are located to the surface of the reflector. The lengths of the sides of the frames (along the axis of the wire):
- AC (AD, BE, BF) = 156 (140) mm
- CN (DM, EN, FM) = 192 (172) mm
The result is simple antenna with an input impedance of 300 Ohm, with a gain of 9.5 ± 0.5 dBi and a bandwidth of 470-760 MHz according to the SWR criterion< 2. Антенна проста в изготовлении, имеет очень хорошую повторяемость, не требует настройки и может быть изготовлена своими руками из самых доступных материалов. В сравнении с классической антенной Харченко этот вариант имеет следующие особенности:
- much wider operating band with comparable gain;
- possibility of direct connection to points N and M of plate symmetrizers or SWA/PAE/ALN amplifiers;
Unfortunately, such an antenna does not cover the full range of 470-860 MHz, therefore, if in the area where the anonymous person lives, some multiplexes operate at frequencies above 750 MHz - it is desirable to recalculate the antenna upwards, reducing all dimensions by 10%, sacrificing gain on the lower channels 21-25. This version of the frame size is indicated in brackets on the drawing.. The dimensions of the reflector and the gap at the connection point in this case do not change.
In comparison with the designs popular on the Internet - the Triple Square and the Turkin antenna - this version of the Kharchenko antenna has undeniable advantages, such as broadband with comparable gain, uncritical to dimensional accuracy, ease of manufacture. Moreover, we do not recommend repeating the above designs for receiving digital television, you can learn more about this. 
With a reflector size of 40x50 cm, the aperture utilization factor reaches 130% in the lower channels, i.e. for such a gain, this is a fairly compact antenna and its dimensions are fully justified by the achieved gain. The width of the main lobe of the radiation pattern is about 70°. 
As a vibrator, you can use a common copper or aluminum electrical wire 4 mm 2 (Ø2.25 mm) or 10 mm 2 (Ø3.57 mm), with a margin of 1.5 meters of wire is enough. A thicker conductor is preferred due to stiffness and added load capacity. You can use other improvised materials - galvanized or brass tapes. As a reflector, you can use a construction galvanized mesh with cells of 20x20 or 20x50 mm. If the antenna is hidden from the wind (for example, in the attic, balcony, close to the facade), the reflector can be made of solid galvanized tin. The tops of the vibrator (points A and B) should preferably be mounted on metal racks / bolts, then the vibrator will be connected to the reflector and the mast along direct current, which contributes to the flow of static charges to the grounded mast, and not to the symmetrizer and then to the television cable. Antenna parameters do not differ for a grounded peak and for an isolated one. Because galvanized mesh does not have rigidity and load-bearing capacity; to maintain its shape, it is necessary to make 2 horizontal crossbars (from a duralumin corner or strip) at the level of the tops of the vibrator. Attach the vibrator mounting posts to these horizontal struts. The technological gap N-M in the center can be varied within small limits depending on the box used, in which the symmetrizer (balun) or antenna amplifier type SWA / PAE / ALN will be hidden. 
A few words for those who consider home-made antennas to be a relic of the "scoop" and "collective farm-garage" culture. Let's just say that in the civilized world, to which such anonymous people often appeal, home-made antennas are developed and made by astrophysicists (like the Hoverman antenna) and professors of medicine, and do not sit and wait until the uncle does it and brings the finished antenna to the market. That's why the world is getting civilized, folks.
P.S: Helpful information for antenna designers from yurik82:
There is no ready-made solution for covering the modern UHF range in the works of Kharchenko and Kismereshkin, because at that time, the usable frequency range was smaller and there was no need for such antennas. BiQuad Kharchenko with a fixed frame perimeter with full symmetry of the double frame has 4 main degrees of freedom:
- distance from the center of symmetry to the vertex A(B);
- distance from the center to the CD(EF) line;
- the length of this line;
- distance from the frames to the reflector;
In order to choose these dimensions optimally (to maximize the gain while limiting the SWR<2), использовалcя разработанный Николаем Младеновым скрипт Python для движка NEC2:
http://clients.teksavvy.com/~nickm/scripts.html
Using non-linear programming methods, such a script automatically goes through tens of thousands of combinations of "antenna degrees of freedom". The result is an antenna model in which the desired properties are maximized.
The end result was also tested in the Ansys HFSS simulator (results in 4NEC2 and HFSS are exactly the same)
https://ypylypenko.livejournal.com/20678.html
Buy or not a decimeter antenna for watching digital TV? The question may seem strange, but on closer examination it becomes more reasonable. So, point by point:
- Where is the guarantee that the purchased antenna is worth the money spent on its purchase?
- When using a purchased decimeter television antenna in the country, you will most likely have to carry it back and forth with you in order to avoid theft.
- The need for such a device may arise spontaneously, somewhere on a picnic, and a trip to a special store is simply undesirable or impossible.
You can solve the problem with receiving the terrestrial television signal of the decimeter range using a home-made antenna for digital TV.
Types of dvb t2 antennas
Standard t2 dmv television - at the moment the newest mass used to transmit a digital signal. Its feature is a significant simplification of the receiving and transmitting devices through the use of decoding devices, the so-called tuners, some TV models already have a built-in digital signal decoding module. Significantly reduced signal power requirements, even a low power signal is sufficient to reproduce high quality images, so there is almost always no need for an amplifier, it becomes unnecessary.
Antenna Kharchenko
Consider the device of a zigzag waveguide, the device of which was proposed by the enthusiast-engineer K. P. Kharchenko back in 1961 in the journal Radio. Outwardly, this device looks like a double rhombus or square adjacent to each other with open corners; the central core and the braid of the coaxial cable are connected at the junction points.
To amplify the signal, you can use a metal reflector - a mirror that reflects a distant signal to the device. Digital Antenna Dimensions do-it-yourself depend on the wavelength of the received signal, it is clear that for the decimeter wavelength range and the dimensions of the dvb t2 antennas with their own hands will be within a few decimeters. The higher the reception frequency, the shorter the wave, the smaller the size. A room waveguide for receiving channels will have side dimensions of approximately 11 and 15 centimeters, overall external dimensions of 30 by 17 cm, and reflector dimensions of 50 by 50 cm.
For its manufacture, a little more than a meter of conductor is required - a copper or aluminum wire or tube with a diameter of 5-6 mm, preferably up to 10 mm or a strip, comparable width. The distance between the open points of the contact angles is 1–2 cm, the distance to the reflector is about 5–7 cm. This will be a long-range waveguide that allows you to receive 20 or more programs. The length of the television cable affects the operation of the antenna, if the cable is over 5-7 meters, you will need an amplifier, which one you choose.
- During operation, the waveguide should be turned towards the nearest transmitting station, during the first installation it is worth experimenting with the orientation of the device, achieving stable signal reception.
This type of antenna can also be successfully used to receive a weak signal from a cellular network, only the dimensions of the device will be several times smaller. There are enough online calculators on the network to calculate specific parameters for each case.
Travel antenna
To make this homemade product, in addition to a plug for connecting to a TV receiver, you only need two identical empty half liter metal cans from drinks. Instead of a coaxial cable, you can take the usual "noodles" for landlines. In the region of the neck of each empty and dry can, one “noodle” wire is fixed with a self-tapping screw, or a braid of a television cable is screwed to one, and its core to the other. The banks are located on one straight line, the reception is adjusted by changing the distance between them from 1 to 8 cm, as well as the exact orientation in the direction of the emitter. The device should not be placed too close to the TV.
If you don’t want to bother with any needlework, and it’s a pity to spend extra money, then you can arrange a very simple device. But it will work steadily where the signal level is quite high. You will need to know the digital broadcast frequency in order to determine the wavelength. To do this, 300 is divided by the number of megahertz of the “numbers” broadcast frequency and a fairly accurate value in meters is obtained. For a frequency of 480 MHz, the wavelength will be 0.625 m, and for 700 MHz - approximately 0.430 m. When even the broadcast wavelength is reluctant to recognize, we simply take 0.63 m, the largest possible.
A piece of coaxial cable is taken equal to the calculated wavelength, the ends are stripped from the outer insulation so that there is access to the braid. The cut piece is bent into a broken circle - there should be a gap of 1-2 cm between the stripped ends and fixed in any way, as simple as possible, even on a cardboard box. On the first side, the central core of another piece of the same cable is soldered, on the other - a braid. A plug is attached to the end opposite the soldering point. Connect and enjoy watching digital broadcasting.
In order to independently make an antenna for dvb t2 with your own hands, it will not take much time and special costs, but the result will please.