Log-periodic antenna UHF: characteristics, principle of operation, making compact models with your own hands

Despite the fact that cable and satellite television is developing at a rapid pace, the reception of on-air broadcasting is still relevant. For their operation, it is not at all necessary to buy a specialized product, a high-quality log-periodic UHF antenna can be assembled by hand. The manufacturing process itself must take place in accordance with elementary requirements and rules, which are designed to protect the master from serious mistakes.

a brief description of

Every master knows that almost the entire volume of television broadcasting takes place in the UHF range. This trend is due to the economic side, since the antenna-feeder economy of broadcasting stations, and the need for regular highly qualified service. In addition, multifunctional TV transmitters cover almost everything with their powerful signal. settlements, and a well-developed network ensures the delivery of the program to the most remote corners country.

Innovative systems have influenced the fact that the method of broadcasting radio waves in large cities has changed significantly. On a high-quality UHF antenna of the decimeter range, common interference affects quite weakly, but high-rise buildings from reinforced concrete act as specific mirrors, which transform the signal several times and even cause its premature attenuation. Despite the possible difficulties, there are many different television programs on the air, which cannot but please the end user.

Separately, it is worth noting the fact that specialists have developed a universal digital broadcasting. The DVB - T2 signal belongs to a special category. Digital TV broadcasting is practically not sensitive to interference, but with phase distortions or mismatch with the cable, the final picture may crumble into small squares even with a clean signal.

Difficulties of choice

Many people think that choosing the right antenna for the decimeter range is quite simple, but in practice, everything is different. The main difficulties are associated with the fact that it is best to test such a product in the conditions in which it will be used. This is due to the fact that each area is characterized by an individual passage of the radio signal.

Experts say that in laboratory conditions TV antennas show some results, but in everyday life they are completely different. There is a certain scheme among experienced craftsmen, thanks to which it is possible to accurately determine the quality of work of both meter and decimeter products.

Of course, no seller will agree to give several antenna models to test their performance at home. In this case, those characteristics that are indicated by the manufacturer in the accompanying documentation come to the rescue. As for the decimeter antenna, it is designed for the beam pattern. The main parameters are auxiliary (side) petals, as well as their width. Chart parameters are defined both in the horizontal and vertical planes at the level of 0.7 of the maximum indicator.

The consumer can test various designs of receiving devices, but for this he need to create a level playing field:

• The cable that connects the TV to the antenna must have the same resistance level and length. It is advisable to use one wire, only the receivers can be changed.
• The master must maintain the direction to the main source of the broadcast signal with high accuracy. To do this, you can mark the attachment pipe.
• An important role is played by the installation site of the antenna. For these purposes, a balcony, roof or roof can be used. The main thing is that the height and place of installation are identical for all products.
• All measurements should be recorded under the same weather conditions.

Depending on the width of the main lobe, the DVM antenna can be directional or non-directional. This parameter is determined by the ratio of the allocated power, provided that the load is matched at the time of receiving a signal from the main source. The shape of the diagram largely depends on the antenna design and the number of directors.

main parameters

Both outdoor and indoor UHF antenna must meet a number of characteristics. Only a high quality product can provide the end user with a clear TV signal.

Moreover, modern requirements for television antennas have changed significantly:

• Experts say that in most cases it is the range type of product that is considered the most suitable, all the necessary settings should be saved exclusively in automatic mode. Everything should depend solely on the territory of the location, and not on engineering tricks.
• Directional and protective action coefficients should not have determinative values. This rule arose against the background of the fact that there is a lot of unnecessary things in the modern air, due to which some kind of interference can pass along the side lobe of the diagram used. You can only deal with such problems with the help of electronics.
• The frequency response should be smoother and more stable. This rule is based on the fact that sharp jumps and dips will inevitably lead to phase distortion.
• Antenna gain plays a special role. Experienced craftsmen are well aware that a product that can cover the entire broadcast gives an excellent reserve of power of the previously received signal. In addition, the equipment will be able to eliminate all signals and noise.
• The purchased TV antenna must be combined with the cable in all its operating ranges without the use of additional units for balancing and matching.

All these points are relevant for both analog and digital television.

Functionality

The standard modern decimeter antenna is presented as a specific set high quality elements: active and passive installation, as well as several directors, mounted on one boom. The active element (vibrator) always differs in its length, this part is located in the electromagnetic field of a certain radio signal, due to which it actively resonates at the frequency of the received signal. This device contains a specific electromotive force (EMF).

As for passive elements, they are affected by an electromagnetic field, which leads to the formation of (EMF). As a result, they independently emit secondary electromagnetic fields. They induce additional electromotive force on the active element. All dimensions of passive parts and their distance to the vibrator must be selected in such a way that the EMF induced by them is in the same phase with the primary electromagnetic background.

For the reflector to function properly, its length must be 15% longer than the vibrator. Such an antenna will have a one-way directional pattern in the horizontal and vertical planes. Thanks to this, the technician will be able to reduce the level of reception of reflected signals and fields, which always pass from the thick side of the antenna. If the device is used for operation over long distances or in difficult conditions where there is a lot of specific interference, then a three-element antenna must be used. The composition of such a product should include a reflector, an active vibrator and at least two directors.

Homemade antenna options

Despite the fact that the modern market offers all consumers a huge assortment of various products for receiving a TV signal, many craftsmen prefer to make them with their own hands. This trend has arisen against the background of the fact that ready-made homemade antennas have all the necessary operational and technical characteristics. In addition, the master significantly saves his financial savings.

Original product made of copper wire. In the arsenal of experienced craftsmen there is a high-quality and at the same time very simple version of a TV antenna, for the manufacture of which you need to prepare only a piece of wire and a soldering iron. We are talking about a narrow-band frame loop. This antenna has a significant advantage - it acts as a powerful selective filter that reduces interference. Thanks to this, the device can receive a high-quality signal.

To avoid common mistakes, you need to correctly determine the length of the loop. This can be done thanks to digital data, which is individual for each region. For example: in St. Petersburg the broadcast takes place at 666 and 586 MHz. But, regardless of the region of residence, the calculation formula is always the same: lr = 300 / f. The length of the working loop in meters is denoted as lr, but the middle frequency range is f. The last value for St. Petersburg can be set as follows (666 + 586) / 2 = 626.

When all the data is available, you can safely determine the optimal length: lr 300/626 = 0.48, which means that the master will need 48 centimeters of wire. To make the finished product better and more durable for its manufacture, you can take a powerful RG-6 cable, where there is a special foil in the braid.

Making such an antenna must comply with the following scheme:

• Initially, the master must cut a piece of wire or cable RG -6, the length of which must fully correspond to the received data lr.
• A working loop of a suitable diameter is carefully rolled up, and after that a cable is soldered to it, which goes to the receiver. If the master decided to use a more durable RG -6, then before using it, the insulation must be removed from both ends (by about 2 centimeters). It should be noted that the center conductor does not need to be cleaned as it is not used for soldering.
• The finished receiver is installed on a special stand.
• A special plug (F-connector) is screwed onto the cable itself, which leads to the receiver.

An important fact is that, despite all the simplicity of the design, this particular type of antenna is one of the most effective for receiving a digital signal. But, provided that all calculations were made as correctly as possible.

Compact model

Despite the unusual design of this antenna, it is quite efficient, as it is presented in the form of the most common dipole. The huge advantage is that the size of a standard beer can is ideal for the arms of an active decimeter vibrator. When the finished product is installed indoors, the master does not need to coordinate the design with the cable (if its length does not exceed two meters).

Experienced craftsmen point out that the shoulders of such an exotic dipole should always be fixed on a holder, which can be made of any insulating material. In this case, home craftsmen often use various improvised things (for example: a bar from a mop, a plastic clothes hanger, a wooden block). The distance between the shoulders should be from 1 to 9 cm (selected exclusively empirically). The main advantages of the design include the speed of its production - a maximum of 25 minutes, as well as the excellent quality of broadcasts.

Universal rhomboid signal receiver

This is one of the simplest, but at the same time, durable and reliable antennas, which was in great demand in the era of terrestrial television broadcasting. The device itself is presented in the form of a simplified model of the classic zigzag.

Experts have found that to increase the sensitivity, the unit must be completed with capacitive inserts, as well as a powerful reflector. If the level of acceptance is at a high level, then there is no need to equip the product with additional elements.

As the main material, you can safely use brass, aluminum or copper tubes / strips 15 millimeters wide. If the master installs the finished structure on the street, then it is better to refuse aluminum products, since they are most susceptible to the negative effects of corrosion. Special capacitive inserts are made of durable sheet metal, ordinary foil or metal mesh. After installation, they must be soldered along the entire circuit. Professional cable laying also has its own nuances: the wire should not have any bends, and it should not leave the side insert.

It is not so difficult to make a high-quality log-periodic UHF antenna on your own, the main thing is adhere to the elementary recommendations of specialists. Moreover, the installation of finished structures can take place both in the house and on the roof. But, it is important to remember that the higher the antenna is located, the better the quality of the received signal will be.