Do-it-yourself decimeter antenna for T2. How to make a decimeter antenna with your own hands? Loop Vibrator - Single Channel Antenna
The era of digital signals has arrived. All broadcasting TV companies began to work in a new format. Analog TVs are dying out. They are still in working condition and are available in almost every family.
In order for the old models to successfully finalize their resource, and for people to use them when watching digital broadcasting, it is enough to connect the DVB-T set-top box to the TV receiver and pick up TV wave signals with a special antenna.
Any home master is able not to buy an antenna in a store, but to make it with his own hands from improvised means for watching digital TV programs at home or in the country. The two most accessible designs are described in this article.
A bit of theory
The principle of operation of the antenna for digital packet television
Any television signal propagates in space from the emitters of the transmitting TV tower to the TV antenna as an electromagnetic wave of a sinusoidal shape with a high frequency, measured in megahertz.
When an electromagnetic wave passes through the surface of the receiving beams of the antenna, a voltage V is induced in it. Each half-wave of the sinusoid forms a potential difference with its own sign.
Under the action of an induced voltage applied to a closed receiving circuit of the input signal with resistance R, an electric current flows in the latter. It is amplified and processed by the digital TV circuitry and output to the screen and speakers as picture and sound quality.
For analog models of TV receivers, an intermediate link works between the antenna and the TV - the DVB-T prefix, which decodes the digital information of the electromagnetic wave into a normal form.
Vertical and horizontal polarization of digital TV signal
In television broadcasting, state standards adopted electromagnetic waves to radiate in only two planes:
- horizontal.
In this way, the transmitters direct the radiating signals.
And users simply need to rotate the receiving antenna in the desired plane to maximize the power potential removal.
Requirements for a digital packet television antenna
TV transmitters propagate their signal-waves over short distances, limited by a line-of-sight zone from the top point of the TV tower emitter. Their range rarely exceeds 60 km.
For such distances, it is sufficient to ensure the power of the emitted TV signal of a small value. But, the intensity of the electromagnetic wave at the end of the coverage area should form a normal voltage level at the receiving end.
A small potential difference, measured in fractions of a volt, is induced on the antenna. It creates currents with small amplitudes. This imposes high technical requirements for the installation and workmanship of all parts of digital reception devices.
The design of the antenna must be:
- made carefully, with a good degree of accuracy, eliminating the loss of electrical signal power;
- directed strictly along the axis of the electromagnetic wave coming from the transmitting center;
- oriented according to the type of polarization;
- it is protected from extraneous interference signals of the same frequency coming from any sources: generators, radio transmitters, electric motors and other similar devices.
How to find out the initial data for calculating the antenna
The main parameter affecting the quality of the received digital signal, as can be seen from the explanatory first figure, is the length of the electromagnetic radiation wave. Under it, symmetrical arms of vibrators of various shapes are created, and the overall dimensions of the antenna are determined.
The wavelength λ in centimeters can be easily calculated using a simplified formula: λ=300/F. It is enough just to find the frequency of the received signal F in megahertz.
For this, we will use the Google search and ask it for a list of regional TV communication points for our area.
As an example, a fragment of the data table for the Vitebsk region is shown with a red rectangle highlighting the transmitting center in Ushachi.
The frequency of its wave is 626 megahertz, and the type of polarization is horizontal. These data are sufficient.
We perform the calculation: 300/626 \u003d 0.48 m. This is the length of the electromagnetic wave for the antenna being created.
We divide it in half and get 24 cm - the desired half-wave length.
The tension reaches its maximum value in the middle of this section - 12 cm. It is also called amplitude. Under this size, a whip antenna is made. It is usually expressed by the formula λ/4, where λ is the length of the electromagnetic wave.
The simplest TV antenna for digital television
It will require a piece of coaxial cable with a characteristic impedance of 75 ohms and a plug to connect the antenna. I managed to find a ready-made two-meter piece in an old stock.
From the free end with an ordinary knife, I cut off the outer shell. I take the length with a small margin: when adjusting, it is always easier to bite off a small segment.
Then I remove the shielding layer from this section of the cable.
The work is done. It remains to insert the plug socket into the connector on the TV signal set-top box and direct the bare wire of the inner core across the incoming electromagnetic wave, taking into account horizontal polarization.
The antenna should be placed directly on the windowsill or fixed on the glass, for example, with a piece of adhesive tape or tied to the blinds. Reflected signals and interference can be shielded with a strip of foil located at a small distance from the central core.
Such a design is done literally in ten minutes and does not require special material costs. It's worth trying it out. But, it is able to work in the zone of reliable signal reception. My building is screened by a mountain and a multi-storey building. The transmitting TV tower is located at a distance of 25 km. Under these conditions, the digital electromagnetic wave is reflected many times and is poorly received. I had to look for another technical solution.
And for you, on the topic of this design, I suggest watching the video of the owner Edokoff “How to make an antenna for digital TV”
Antenna Kharchenko at 626 MHz
To receive analog broadcasting signals of various wave frequency ranges, the design of a zigzag broadband antenna, which does not require complex manufacturing, worked well for me before.
I immediately remembered one of their effective varieties - the Kharchenko antenna. I decided to use its design for digital reception. The vibrators were made from a flat copper bar, but it is quite possible to get by with a round wire. This will make it easier to bend and align the ends.
How to determine the dimensions of a particular antenna
Online calculator
Let's use the all-knowing Google search. We write on the command line: "Calculation of the Kharchenko antenna" and press Enter.
Choose any site you like and perform an online calculation. I went to the first one that opened. Here's what he gave me.
I presented all his data with a picture with the designation of the name of the size of the Kharchenko antenna.
Manufacture of antenna design details
I took the information provided as a basis, but did not accurately withstand all dimensions. I know from previous practice that the antenna works well in the broadband wave range. Therefore, the dimensions of the parts are just slightly overestimated. The half-wave of each harmonic of the sinusoid of the electromagnetic TV signal will fit into the shoulder of each vibrator and will be accepted by it.
Based on the selected data, I made blanks for the antenna.
Vibrator Design Features
The connection of the ends of the shank for the "eight" was created in the center at the bending stage. Soldered them with a soldering iron.
It was created for me according to the “Moment” principle, made with my own hands from old transformers, it has been working for two decades. I even soldered a copper wire of 2.5 squares to them in a thirty-degree frost. Works with transistors and microcircuits without burning them.
I plan to describe its design in the near future in a separate article on the site for those who also want to make it with their own hands. Follow the publications, subscribe to notifications.
Connecting the Antenna Cable to the Vibrator
I simply soldered the copper core and braid to the figure-eight metal from different sides in its center.
The cable was tied to a copper bar, bending it with a loop in the shape of a semi-square vibrator. In this way, the resistance of the cable and antenna is matched.
Shielding grid design
In fact, the Kharchenko antenna often works fine without signal shielding, but I decided to show its manufacture. For the base, I took a wooden block. I did not paint and impregnate with varnish: the structure will be used indoors.
I drilled holes in the back side of the bar for attaching the screen wires and inserted them, and then wedged them.
The result was a screen for Kharchenko's antenna. In principle, it can also be made of a different design: cut out of a piece of the frontal armor of a tank or cut out of food foil - it will work in about the same way.
On the reverse side of the bar, I fixed the design of the vibrator with the cable.
The antenna is ready. It remains to install it on the window to work in vertical polarization.
When a television receiver is at a great distance from the transmitting generator, then the power of its signal gradually weakens. It can be increased by special electronic devices - amplifiers.
You just need to clearly see the difference between the signals received by the antenna, which can be:
- just weakened;
- contain high-frequency interference that distorts the shape of a digital sinusoid to the shape of some kind of "karyabola".
In both cases, the amplifier will fulfill its role and raise the power. Moreover, the TV will clearly perceive and show a weakened signal, and with an enhanced “karyabola”, playback problems will arise.
To eliminate such wave interference are called upon:
- h/h filters;
- screens.
They must be measured with an oscilloscope, and the ways of using various designs should be analyzed in each specific case individually. The antenna is not to blame.
Digital technology is already "walking the country" with might and main, and many are eager to buy TVs that support this format. But if this is not possible, there is another way out - to make the antenna yourself. With a little theoretical and practical training, almost anyone can do it.
How to make your own dvb -antenna
Digital technologies involve the transmission of image and sound through digital video encoding. It differs from analog equipment in that the interference practically does not interfere with the signal, so it enters the receiver device with minimal losses.
To date, there are already 20 channels of this type. To be able to connect to it, it is not necessary to have special equipment. In this case, we are talking about receiving a high-quality signal, for which it will be enough to have a television cable. It is also called coaxial. 
To receive a digital signal, you need a decimeter antenna. It is very simple to do it yourself - you only need an antenna cable. But the main thing is not to make mistakes in the calculations. The procedure is as follows:
- Take 30 cm of antenna cable and connectors (male/female and F-connector).
- Prepare wire cutters, a tape measure (at worst, a ruler), a knife and a calculator.
- Next, you will need a computer with an internet connection. Find a coverage map of dvb channels on the digital television website, determine which one is closest to your city. There is a search form.
- Find a station, find out the detailed frequencies on which it operates.
- There may be specified several channels and frequencies for them. The antenna length is calculated when 7500 is divided by the frequency. For example, if the channel frequency is 754 MHz, then 7500:754=9.94 is obtained. Thus, it turns out that a home-made dvb antenna should be about 10 cm long. If there are several stations, the average length is determined.
- Attach the F-connector to the end of the antenna wire with your own hands. It's easy - the cable is stripped, the connector is screwed on top. It is necessary that there is a central wire in the middle, and a foil with wires at the attachment point.
- A few centimeters further recede from the connector, then measure another 10, and cut off the unnecessary.
- The plastic insulation and the "screen" (wiring with foil) are removed from the remaining cable, the antenna is ready. Now the question is its connection.
There is another manufacturing method, which is also simple and requires a minimum of materials at hand: a plank of about 550x70 mm, self-tapping screws, copper wire (40 cm long, central core 4 mm in diameter). A piece is made from wood. 8 wires, each 375 mm long, stripped in the middle by about 30 mm, thus providing good conditions for signal reception. Then you need to cut two wires 220 mm long, and clean the joints according to the size of the plank. The remaining wires are bent with the letter "V".
A special plug connects the antenna and the cable (the plug can be purchased separately). The wire is fixed on the plug with a desktop soldering iron. Homemade antenna is ready.
The third method will require the presence of:
A small incision is made in the cable sheath, 10 cm from the edge, twist the covering “foil”, cutting off the middle layer by 10 mm. 
From the opposite end, install the plug to connect to the TV. A cable is attached to one of the cans, the middle of the wire is screwed to the second, and best of all by soldering, the adhesive tape is unreliable.
Fasten the jars in a straight line on the trempel at a distance of about 7-8 cm. Now the device must be fixed in the place of the clearest reception of the television signal. True, such a device will not be able to catch many channels, a maximum of 10.
Feature and dvb connections -antennas
The difficulty may lie in finding such a point in the apartment where the digital television signal would be best caught. 
Then sometimes there are problems in order to insert the antenna into the set-top box or TV. Options - for example, first insert an extension cord into the console, and then the cable is inserted into it. At the same time, it should not interfere with anyone, ideally it is generally better to hide it somehow.
Self-made designs of this kind, apparently, do not take much time. So for about 100-400 rubles you can build a do-it-yourself digital television device of the dvb standard. According to reviews, it works even better than various expensive telescopic devices. True, only for digital TV of one frequency. Not suitable for analog. A high-quality image can be obtained provided that a powerful transmitting station is located no further than 30 km. True, sometimes the distance is reduced even to a range of 5-10 km.
Features of dvb reception
There are also home-made ways to amplify the signal, especially if the terrain or a great distance from the transmitter (50-100 km.) Does not allow you to get good digital TV reception. For a high-altitude external antenna, you will need to install a board, and any two-transistor with a low or medium gain will do. Powerful amplifiers in this case are not required, since the signal is quite distorted. 
If you suddenly need a television antenna during your stay in the country or on vacation, but there was no factory model at hand, you can do without your favorite TV programs, but it is much more interesting and faster to make such a device yourself. It can be made to receive certain channels in the meter or decimeter range. Next, we will look at how a do-it-yourself TV antenna is made in several ways, from which you can choose the most suitable one for yourself.
A fairly simple version of an indoor antenna, which can be easily implemented at home in a short period of time. Designed to receive television channels broadcast in the UHF range. To make it, you will need a piece of coaxial cable, plywood or other sheet material as a base, electrical tape for fixing, a knife and a soldering iron.
Rice. 1: Coaxial cable antenna
- Take a piece of coaxial cable 0.53 m long and bend it in the form of a ring (1) with open edges and fix it in this form on a sheet of plywood;
- From the same cable, cut a 0.175 m piece for the loop (2) and connect as shown in the figure.
- Connect the cable (3), on the other end of which install a connector for connecting to a TV.
The simplest antenna is ready, but it may not be enough to receive a signal, so you will need an active gain block. Or make a more complex figure-eight model.
Antenna "eight"
A fairly simple version of a homemade antenna, it can be assembled within a few minutes. To do this, you will need any cardboard box, in this case it is used from under shoes, a plug, a stationery knife, a soldering iron, adhesive tape, foil and glue.
The manufacturing process consists in the following steps in turn:
- Open the box and clean the inner surface of accumulated dust and debris, if they are absent, you can immediately proceed to pasting.
- Apply a thin layer of glue to the bottom of the box, it is important that it does not change the geometric parameters of the foil located on it. Paste the bottom with foil - it will act as a signal reflector.
Rice. 2. Cover the bottom of the box with foil - Close the box and seal it with tape so that it cannot open spontaneously.
- Install two pieces of cable in the shape of a figure eight on the cover, fix the sides of which with tape.
Rice. 3: make a figure eight and fix with tape - In the middle of the figure eight, strip the cable and make two leads from the metal braid to connect the antenna.
Rice. 4: in the middle of the figure eight, trim the ends - Cut a piece of conductor to connect the antenna to the TV, its length is selected according to the distance from the installation site to the TV or.
- Strip one end of the connecting cord under the connector, strip the second in such a way as to collect the output from the screen and the output from the central core through 1 - 2 cm of insulation.
Rice. 5: strip the cable - Connect the cable leads to the figure eight leads as shown in the figure.
Rice. 6: connect cable pins to figure eight pins
Connect the TV connector to the second end, and connect to the TV.
The G8 antenna is ready for use, today it will be an excellent replacement for satellite television, since the picture of a digital signal is in no way inferior to it.
Double and triple square
Unlike the previous version, assembling the antenna in the form of a double and triple square will require much more effort. But such a device will allow you to receive even weak television signals, the main thing is to ensure accurate orientation to the repeater. At the same time, the quality does not depend on the distance to the source, the main thing is to observe the overall dimensions. For its manufacture you will need: metal tubes (copper, brass, aluminum) or rods, a dielectric rod, a wooden base for the supporting structure, connecting wires.
Depending on the diameter of the tubes, the antenna will be able to receive a different number of channels in a certain frequency range:
- 10 - 20mm is suitable for reception in the meter range, can catch from 1 to 5 channels.
- 8 - 15mm is suitable for reception in the meter range, can catch from 6 to 12 channels.
- 3 - 6mm is suitable for channels in the decimeter range.
Rice. 7: double and triple square antenna circuit As you can see in the figure, structurally, a double and triple square is two and three regular-shaped frames that differ in size. Depending on the overall dimensions, the length of the received wave will also change.
| Wavelength | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| IN | 1450 | 1220 | 930 | 840 | 770 | 410 | 390 | 370 | 360 | 345 | 330 | 320 |
| R | 1630 | 1370 | 1050 | 950 | 870 | 460 | 440 | 420 | 405 | 390 | 375 | 360 |
| A | 900 | 760 | 580 | 530 | 480 | 250 | 240 | 230 | 220 | 210 | 210 | 200 |
| W | 1500 | 1260 | 970 | 880 | 800 | 430 | 410 | 390 | 375 | 360 | 350 | 335 |
| Channels, pcs | IN | R | A | W |
| 21-26 | 158 | 170 | 91 | 152 |
| 27 – 32 | 144 | 155 | 83 | 139 |
| 33 – 40 | 131 | 141 | 75 | 126 |
| 41 – 49 | 117 | 126 | 68 | 113 |
| 50 – 60 | 105 | 113 | 60 | 101 |
For a triple square, the dimensions are shown in the table below
Table: dependence of dimensions on the received wave of the meter range, mm
| Channels | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| D | 1255 | 1060 | 825 | 750 | 688 | 370 | 354 | 340 | 325 | 312 | 300 | 290 |
| IN | 1485 | 1260 | 975 | 890 | 812 | 438 | 418 | 400 | 385 | 370 | 357 | 345 |
| R | 1810 | 1530 | 1190 | 1080 | 990 | 532 | 510 | 488 | 470 | 450 | 435 | 420 |
| A | 630 | 532 | 412 | 375 | 345 | 185 | 177 | 170 | 163 | 157 | 150 | 145 |
| B | 915 | 775 | 600 | 545 | 500 | 270 | 258 | 246 | 237 | 228 | 220 | 210 |
| W | 1500 | 1260 | 970 | 880 | 800 | 430 | 410 | 390 | 375 | 360 | 350 | 335 |
Table: dependence of dimensions on the received wave of the decimeter range, mm
| Channels, pcs | D | IN | R | A | B | W |
| 21-26 | 134 | 158 | 193 | 67 | 98 | 152 |
| 27 – 32 | 122 | 144 | 176 | 61 | 89 | 139 |
| 33 – 40 | 110 | 131 | 160 | 55 | 80 | 126 |
| 41 – 49 | 99 | 117 | 143 | 50 | 72 | 112 |
| 50 – 60 | 89 | 105 | 129 | 45 | 65 | 102 |
The short-circuited bridge shown in the figure is designed to connect a symmetrical frame to an unbalanced cable and acts as a matching block.
The manufacturing process consists of the following steps:
- Bend the tube into squares according to the given dimensions;
- Connect them at the top with an arrow of conductive material, and at the bottom with an arrow of dielectric material;
- Install the outdoor antenna on a wooden base;
- Cut the cable and separate the braid into a separate terminal;
- Connect the cable to the antenna, and terminate the other end under the antenna plug to transmit television broadcasts to the TV.
The antenna is ready, this option is suitable for outdoor placement, so it is best to install it on a roof or a free-standing support.
From metal cans
If you can find a pair of even beer cans made of tin or aluminum at home, then you have the opportunity to quickly assemble a good TV receiver. To do this, you need to take two cans of as large a volume as possible, a good result will be achieved with a volume of 1 liter, but if they are not available, then 0.5 liters will do, a screwdriver or a screwdriver with a pair of self-tapping screws, a soldering iron, adhesive tape, a television cable, a base made of dielectric material (in this case, a wooden trempel is used).
The process of manufacturing an antenna from metal cans consists of the following steps:
Make loops for connecting at the output of the braid and core.
After installation, you should configure the channels by changing the distance between the banks. The optimal position is selected based on the quality of the signal on the TV. Such an antenna will receive about seven analog TV channels.
framed
To make such an antenna, you will need aluminum plates, a metal mesh for making a reflector (from a barbecue, for plaster, etc.), bolts with nuts or rivets to fix frame parts, a cable with a plug for connecting to indoor TV, a drill, a screwdriver and pliers.
Rice. 10: frame antenna The manufacturing process of the antenna is as follows:
- Cut the aluminum strips to the desired size and drill holes at the ends for bolting.
- Assemble the frame as shown in the figure above, the joints are overlapped. To prevent oxidation of these points, it is desirable to cover them with paint or varnish.
- Connect a television cable with an antenna connector to points A and B on the antenna.
- Fasten the frame to the reflector, most importantly, pay attention that the latter does not short-circuit the electrical circuit of the antenna itself.
- Install on the mast and place in the place provided for this.
If the signal is weak, you can get a more powerful antenna by including it in the circuit.
In the shape of a butterfly
Another version of the all-wave antenna, which allows you to receive a fairly large number of channels in good quality. Due to this, its work can replace the use, but the manufacturing process also requires utmost attention, accuracy and time. Structurally, it will consist of a wooden board and several pieces of copper wire with a 4mm strand, bent in the shape of butterfly wings, hence the name of the model. Initially, you need to mark the location of the holes on the board and drill them according to the diagram:
Rice. 11: butterfly antenna hole pattern 
The broadband antenna is ready to use, you can install it in the most suitable place in the room to receive TV signals.
Zigzag antenna Kharchenko
This version of the antenna is designed for broadcasting digital television, which is carried out in the decimeter range. The main advantage is that there is either a digital signal or it is completely absent, so the image is of a fairly high quality.
Structurally, Kharchenko's antennas consist of two rhombuses, which are made of conductive materials. Copper or aluminum wire, rod, corner or tire is suitable for them. A schematic representation of a zigzag antenna is shown in the figure below.
Rice. 15: diagram and practical implementation of the Kharchenko antenna In this case, the dimensions must be calculated based on the wavelength. To receive digital broadcasting, the wavelength is divided by 4 - this will be the size of B1, and in order to tune the antenna to a wider band, the B2 side must be made 1 cm smaller than B1, for example, in a ratio of 12.5 and 11.5 cm. For bending copper wire, you can use pliers, a vise or a hammer. There is a reflector on the reverse side of the antenna for better TV signal reception, but this refinement was relevant for analog television, it is not necessary to install it in digital TV.
In addition to the wire for the manufacture of the device, you will need a television cable, a frame for placing the receiver, insulating materials, and a plug for connection. From the tools, take an abrasive wheel or sandpaper, a soldering iron.
The manufacturing process includes the following steps:
- Prepare the wire of the required length, in this case 112mm is used, if you use other sizes, you should not forget about the margin for bending points.
- Bend the wire antenna as shown in the diagram, maintaining 90º angles and making a gentle turn at the bends.
Rice. 16: bend the wire - To connect the ends, make grooves and connect with thin wire or make two loops and connect them together, for better contact and to prevent oxidation, tin them. If there is varnish on the conductor, it should be cleaned off before tinning.
Rice. 17: tin ends - Repeat the same procedure with the opposite side to make a second contact. The distance between them should be about 2 cm.
- Strip the coaxial cable from both sides - one for connection to the antenna, the second for input to the signal receiver. For the antenna, you need to remove the outer insulation by 3 - 5 cm and assemble the multi-wire braid into a separate terminal. For a TV, strip about 1 - 2 cm and solder to the plug.
- Install the antenna on the base and solder the cable to it.
Rice. 18: connect the cable to the terminals - To protect against atmospheric influences and give additional rigidity, the place of soldering is treated with hot melt adhesive.
Rice. 19: treat the place of soldering with hot glue
The antenna is ready for connection to the TV, if all the requirements specified by the designer are met, you will get an excellent version of the device, which is not inferior to the factory models in terms of parameters.
Video ideas
Digital terrestrial television (DVB-Digital Video Broadcasting) is a technology for transmitting television images and sound using digital coding of video and sound. Digital encoding, unlike analog, provides signal delivery with minimal losses, since the signal is not affected by external interference. At the time of 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 about the possibility of catching digital channels on the website www.rtrs.rf. If there are digital channels in your area, in this case, 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 - What antenna to use for digital TV? or How to make an antenna for digital television? In this article, I would like to dwell in more detail on antennas for viewing digital television, and in particular, I will show how to make a digital tv antenna.
The first thing I would like to emphasize is that digital television does not need a specialized antenna, an analog antenna is quite suitable (the one you used earlier to watch analog channels). Moreover, only a television cable can be used as an antenna ...
In my opinion, the simplest antenna for digital television is a television cable. Everything is extremely simple, 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, to do 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.
For more information, please click on the "More Details" button.
Now we need to calculate the wavelength. The formula is very simple:
where, λ (lamda) - 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 used 602 MHz and 610 MHz, for the calculation I will use the frequency 602 MHz
Total: 300/602 ≈ 0.5 m = 50 cm.
Leaving half a meter of the central core of a coaxial cable is not beautiful and inconvenient, so I will leave half, maybe a quarter of the wavelength.
l=λ*k/2
where l is the length of the antenna (central core)
λ- wavelength (calculated earlier)
k - shortening coefficient, 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 coaxial cable.
Here is the result of the work done
Here is what the antenna looks like when installed.
View of the antenna while watching TV.
Despite the rapid development of satellite and cable television, the reception of terrestrial television is still relevant, for example, for seasonal residences. It is not at all necessary to buy a finished product for this purpose; a home decimeter (UHF) antenna can be assembled by hand. Before proceeding to the consideration of designs, we will briefly describe why this particular range of the television signal was chosen.
Why DMV?
There are two good reasons to opt for this type of structure:
- The thing is that most channels are broadcast in this range, since the design of repeaters is simplified, and this makes it possible to install a larger number of unattended low-power transmitters and thereby expand the coverage area.
- This range is selected for broadcasting "numbers".
Indoor antenna for TV "Rhombus"
This simple, but at the same time, reliable design was one of the most common in the heyday of on-air television.
Rice. 1. The simplest homemade Z-antenna, known under the names: "Rhombus", "Square" and "People's Zigzag"As can be seen from the sketch (B Fig. 1), the device is a simplified version of the classic zigzag (Z-design). To increase the sensitivity, it is recommended to equip it with capacitive inserts ("1" and "2"), as well as a reflector ("A" in Fig. 1). If the signal level is acceptable, this is not necessary.
As a material, you can use aluminum, copper, as well as brass tubes or strips with a width of 10-15 mm. If you plan to install the structure on the street, then it is better to abandon aluminum, since it is susceptible to corrosion. Capacitive inserts are made of foil, tin or metal mesh. After installation, they are soldered along the contour.
The cable is laid as shown in the figure, namely: it did not have sharp bends and did not leave the limits of the side insert.
Decimeter antenna with amplifier
In places where a powerful relay tower is not located in relative proximity, you can raise the signal level to an acceptable value using an amplifier. Below is a schematic diagram of a device that can be used with almost any antenna.
Rice. 2. Antenna amplifier circuit for the UHF range Item List:
- Resistors: R1 - 150 kOhm; R2 - 1 kOhm; R3 - 680 Ohm; R4 - 75 kOhm.
- Capacitors: C1 - 3.3 pF; C2 - 15 pF; C3 - 6800 pF; C4, C5, C6 - 100 pF.
- Transistors: VT1, VT2 - GT311D (can be replaced with: KT3101, KT3115 and KT3132).
Inductance: L1 - is a frameless coil with a diameter of 4 mm, wound with copper wire Ø 0.8 mm (2.5 turns must be made); L2 and L3 are 25 µH and 100 µH high frequency chokes, respectively.
If the circuit is assembled correctly, we will get an amplifier with the following characteristics:
- bandwidth from 470 to 790 MHz;
- gain and noise coefficients - 30 and 3 dB, respectively;
- the value of the output and input resistance of the device corresponds to the RG6 cable - 75 Ohm;
- the device consumes about 12-14 mA.
Let's pay attention to the way the power is supplied, it is carried out directly through the cable.
This amplifier can work with the simplest designs made from improvised means.
Indoor antenna made from beer cans
Despite the unusual design, it is quite functional, since it is a classic dipole, especially since the dimensions of a standard can are perfect for the arms of a UHF vibrator. If the device is installed in a room, then in this case it is not even necessary to coordinate with the cable, provided that it is not longer than two meters.
Designations:
- A - two cans with a volume of 500 mg (if you take tin, not aluminum, you can solder the cable, and not use self-tapping screws).
- B - places for fastening the shielding braid of the cable.
- C - central vein.
- D - the place of attachment of the central core
- E - cable coming from the TV.
The arms of this exotic dipole must be mounted on a holder made of any insulating material. As such, you can use improvised things, for example, a plastic clothes hanger, a mop bar, or a piece of wooden beam of the appropriate size. The distance between the shoulders is from 1 to 8 cm (selected empirically).
The main advantages of the design are fast production (10 - 20 minutes) and quite acceptable quality of the "picture", provided that the signal strength is sufficient.
Making a copper wire antenna
There is a design that is much simpler than the previous version, which requires only a piece of copper wire. This is a narrow band loop antenna. This solution has undeniable advantages, since in addition to its main purpose, the device plays the role of a selective filter that reduces interference, which allows you to confidently receive a signal.
Fig.4. A simple UHF loop antenna for receiving digital TV For this design, it is necessary to calculate the length of the loop, to do this, you need to find out the frequency of the “numbers” for your region. For example, in St. Petersburg it is broadcast on 586 and 666 MHz. The calculation formula will be: L R = 300/f, where L R is the length of the loop (the result is presented in meters), and f is the average frequency range, for Peter this value will be 626 (the sum of 586 and 666 divided by 2). Now we calculate L R, 300/626 = 0.48, which means that the length of the loop should be 48 centimeters.
If you take a thick RG-6 cable, where there is a braided foil, then it can be used instead of copper wire to make a loop.
Now we will tell you how the structure is assembled:
- A piece of copper wire (or RG6 cable) is measured and cut off with a length equal to L R .
- A loop of a suitable diameter is folded, after which a cable is soldered to its ends, which goes to the receiver. If RG6 is used instead of copper wire, then the insulation is first removed from its ends, by about 1-1.5 cm (the central core does not need to be cleaned, it does not participate in the process).
- The loop is installed on the stand.
- An F connector (plug) is screwed onto the cable to the receiver.
Note that despite the simplicity of the design, it is most effective for receiving "numbers", provided that the calculations are carried out correctly.
Do-it-yourself indoor antenna MV and UHF
If, in addition to UHF, there is a desire to receive MV, you can assemble a simple multiwave oven, its drawing with dimensions is presented below.
To amplify the signal in this design, a ready-made SWA 9 block is used, if there are problems with its acquisition, you can use a home-made device, the circuit of which was given above (see Fig. 2).
It is important to observe the angle between the petals, going beyond the specified range significantly affects the quality of the "picture".
Despite the fact that such a device is much simpler than a log-periodic design with a wave channel, nevertheless, it shows good results if the signal is of sufficient power.
Do-it-yourself figure-eight antenna for digital TV
Consider another common design option for receiving "numbers". It is based on the classic scheme for the UHF range, which, due to its shape, was called the "Eight" or "Zigzag".
Rice. 6. Sketch and implementation of the digital eight Construction dimensions:
- the outer sides of the rhombus (A) - 140 mm;
- inner sides (B) - 130 mm;
- distance to the reflector (C) - from 110 to 130 mm;
- width (D) - 300 mm;
- step between the bars (E) - from 8 to 25 mm.
The cable connection point is at points 1 and 2. The requirements for the material are the same as for the Rhombus design, which was described at the beginning of the article.
Homemade antenna for DBT T2
Actually, all the examples listed above are capable of receiving DBT T2, but for a change, we will give a sketch of another design, popularly called the “Butterfly”.
As a material, you can use plates made of copper, brass, aluminum or duralumin. If the structure is planned to be installed on the street, then the last two options are not suitable.
Outcome: which option to stop?
Oddly enough, but the simplest option is the most effective, so the "loop" is best suited for receiving the "digit" (Fig. 4). But, if you want to receive other channels in the decimeter range, then it is better to stop at the "Zigzag" (Fig. 6).
The antenna for the TV should be directed towards the nearest active repeater, to select the desired position, rotate the structure until the signal strength is satisfactory.
If, despite the presence of an amplifier and a reflector, the quality of the "picture" leaves much to be desired, you can try to install the structure on the mast.
In this case, it is necessary to install lightning protection, but this is a topic for another article.