How to make a Kharchenko antenna for digital TV with your own hands: calculation, assembly of a biquadrate

Now there is an active change of analog television broadcasting to digital. Since 2012, a single standard for digital television broadcasting
DVB-T2 has been adopted for free viewing. To obtain such an opportunity, it remains only to acquire a receiver-antenna, which you can make yourself. One of the most affordable options for digital TV that you can assemble with your own hands is the Kharchenko antenna.

Features and device of the Kharchenko antenna

The idea of ​​self-manufacturing of the device is based on the development of engineer Kharchenko. The antenna operated in the decimeter range (DCV), popular at the end of the last century. This is an analogue of an aperture antenna based on a zigzag feed. The signal is accumulated with the help of a flat reflector (a solid or lattice screen – a frame made of conductive material), which is at least 20% larger than the vibrator. For self-manufacturing, it will be necessary to take into account the geometric characteristics and selection of a specific material.
The television signal is transmitted using waves with horizontal polarization. A simplified version of the antenna is presented in the form of two horizontal loop vibrators connected in parallel to each other, but disconnected at the place where the feeder (cable) is connected. The dimensions were indicated in Kharchenko’s article “Antenna of the DTSV range”, and the antenna is calculated according to the formulas proposed by the author.

Materials and tools for the manufacture of the Kharchenko antenna

Necessary materials:

• grill grate;
• spray car paint;
• solvent or acetone;
• drills for drills;
• coaxial television cable (no more than 10 meters);
• PVC pipe XB 50 cm with a diameter of 20 mm;
• metal dowels for drywall;
• copper wire for a vibrator with a diameter of 2 to 3.5 mm;
• 2 thin metal plates.

Tools for work:

• soldering iron 100 W;
• screwdriver and nozzles;
• hot glue gun;
• wire cutters, pliers, hammer;
• pencil, tape measure, molar knife.

The vibrator can be made of non-ferrous metals (copper, aluminum) and alloys (usually brass). The material can be in the form of wire, strips, corners, tubes.

We carry out calculations

For the manufacture of the Kharchenko antenna, it is necessary to carry out an accurate calculation using a calculator or formulas. Using this technology, you can calculate the installation of the antenna even with a weak signal – about 500 MHz. First you need to know the frequency of the two DVB-T2 TV broadcast packets in your area. This can be found on the CETV interactive map website. There you need to find the nearest TV tower, as well as available broadcasting (one or two channel packages) and what frequencies are used for this. After finding out the values ​​of the frequencies of the packets, the length of the sides of the square of the designed antenna-receiver is calculated. The drawing and diagram of the antenna are compiled on the basis of the signal transmission frequency. Hertz (Hz) is used to measure it and is denoted by the letter F. As an example, you can use the frequency of television broadcasting of the first and second packets in the city of Moscow – 546 and 498 megahertz (MHz).

Calculator

The calculation is performed according to the formula: speed of light / frequency, that is: C / F \u003d 300/546 \u003d 0.55 m \u003d 550 mm. Similarly for the second multiplex: 300/498 = 0.6 = 600 mm. The wavelength dimensions are 5, 5, and 6 dm, respectively. To receive them, you need a UHF antenna, called a decimeter antenna. After that, it is very easy to calculate the width of the wave across, projected onto the receiver. It is 1/2 of the length, respectively 275 and 300 mm for the first and second packages.

To ensure high-quality reception of a digital signal, each biquadrate edge must be half the width of the wave in diameter. For manufacturing, it is better to use an aluminum core or a copper tube. Ideally, it is better to use copper wire (3-5 mm) – it has a stable geometry and bends well.

Kharchenko antenna calculation for digital TV: calculator and creation methods: https://youtu.be/yeE2SRCR3yc

Antenna assembly

The manufacture of a Kharchenko antenna for digital television broadcasting involves the following step-by-step actions:

1. The polarization and frequency of the wave are determined. The design must be linear.
2. Copper is used as a material for the manufacture of a biquadreceiver antenna. All elements are located at the corners, one of them they must touch. For horizontal polarization, the structure must be placed vertically. With vertical polarization, the device is placed on its side.
3. The copper wire is measured and taken to the required length (+1 cm). A copper or aluminum tube (diameter 12 mm) is suitable. The insulation from the copper core is cleaned. Leveled with a hammer on a hard surface. The middle is measured and bent 90 degrees. If there is a vise, then the wire is clamped and aligned in them. Bends are made according to the calculated dimensions.
4. At one end, a small piece is cut off at a 45 degree angle to form a pointed tip. The second end is bent, the same procedure is done on it. Both squares can be slightly bent at the same time. On the central internal bends, small cuts are machined with a needle file. Then it will be possible to pull together these two free ends and fix them with a thin copper wire.
5. You will need a soldering iron, as well as liquid rosin or flux for tinning the middle bends. This is done on each side of the copper wire.
6. The coaxial cable is stripped by 4-5 cm. The braid or outer conductor is twisted into one wire and wrapped around one of the bends. Solder it to the copper wire. The insulation of the inner conductor is stripped and similarly wrapped around the next bend. Soldering must be done carefully, supporting the insulation with pliers, because the heat can cause it to move out of the way. First, the frame is heated at the place of sealing, and then only the conductor.
7. The cable wiring is fixed with a nylon tie, degreased with a solvent. Sealing areas are isolated with hot glue using a gun. A hair dryer can be used to correct defects in the adhesive formation.
   

   Visually, the inner central corners of the structure, resembling a figure eight, should be close to each other (10-12 mm), but not touching. If an error occurs during the bending of the contour, even by 1 mm, the image may be distorted.

8. The cable is brought to the approach points from two sides. One direction of the diagram must be blocked, for this a copper reflective shield is installed. It is attached to the cable sheath.
9. For the manufacture of the reflector, textolite boards coated with copper were previously used. Now metal plates are used for this. Also, the reflector can be made from a grill grate. You can use a heat exchanger from the refrigerator or a drying rack for dishes. The main thing is that the structure does not rust in the open air. The reflector must be larger than the vibrator frame.
10. The frame is located in the middle of the reflector. For its fastening, you can use two metal plates.
11. The signal at a high frequency propagates along the surface of the conductor, so it is better to cover the antenna with paint. Sealing points are filled with hot glue or sealant.

The receiver must be at a distance from the reflector, calculated by the formula: wavelength / 7. The antenna is placed in the direction of the repeater.

How to make the correct calculations and make the Kharchenko antenna is shown in this video: https://youtu.be/Wf6DG2JbVcA

Connection

One end of the cable with a resistance of 50-75 ohms is soldered to the finished antenna, the other to the plug. It is better to connect the cable to the top of the base, and use the bottom as fasteners. The picture and sound quality of digital TV broadcasting will not depend on how far the transmission will be, unlike analog broadcasting. With the correct manufacture of the antenna, the signal transmission to the receiver will occur in normal quality and there should not be any difficulties. However, if a failure occurs, the signal will completely disappear (sound and picture will disappear). Unlike analog television, digital picture quality is the same across all channels and there can be no difference.

Testing in practice

The assembled antenna must be checked. To test digital TV, on the set-top box in the main menu or on the TV, you need to run auto-tuning of channels. This procedure will only take a few minutes. To search for channels in manual mode, you will need to enter their frequency. In order not to waste time on performing a full search, and also if you already have channels configured, you can facilitate this process. To do this, two channels are selected, each of them sets the frequency of any channel from different packages (each of these multiplexes uses one frequency range to broadcast all TV channels). To test the manufactured device, it is enough to verify the quality of the television broadcast. Good image quality will indicate the correctness of the work. As a result, a high-quality picture will be or obtained,

If interference occurs, you can try to rotate the antenna, observing the change in image quality. When determining the optimal location of the TV antenna, it must be firmly fixed, but always in the direction of the TV tower.

The Kharchenko antenna is a versatile and practical device that provides reception of weak signals. The device can be assembled by hand and used instead of the factory antenna with an amplifier. Making an antenna is within the power of every person. It is enough to find the material, perform the correct calculations and exactly follow the information received in the manufacture of the device.