The antenna is decimeter. Antennas for television. Room antenna DMV. Decimeter antenna with own hands

The modern market offers a huge range of antennas for receiving terrestrial television. There are two main types of these products, allowing to take the meter and decimeter range of radio air. They can also be divided into place of use for outdoor and indoor. In principle, they are not much different. Here, first of all, emphasis is placed on the size and preservation of the necessary parameters under the influence of weather conditions. In this article we will discuss the existing types of these products, consider what parameters they have, and how to conduct testing. And for those who like to make art, we will tell you how a decimeter antenna is manufactured by our own hands.

What's the difference?

Let's try to explain in a few words how to determine what kind of product is in front of you. The antenna of the decimeter band looks like a ladder. Install them parallel to the ground. Metro TV antennas are crossed aluminum tubes. Appearance of both types is presented in the photo below. There are also combined antennas, when both "ladder" and cross tubes are combined.

Problem of choice

It would seem that everything is simple. However, in this case the buyer is faced with the question of how to choose the right device, what parameters to pay attention to. In general, it's best to test TV antennas directly in the conditions in which they will work. Passing a radio signal is often individual for a particular locality. Thus, the product under laboratory conditions shows only one result, and in the "field" it is quite different. There is a certain tactic, which allows testing both meter and decimeter TV antennas. However, when choosing such a product in the store, we do not have the opportunity to conduct a full test. No seller will agree to give us several different antennas for testing. In this case, you have to trust the characteristics of these products. And to hope that the selected antenna will perform its functions according to passport data, and not real conditions.

Main settings

The decimeter antenna is primarily characterized by a directional pattern. The main parameters of this characteristic are the level of the side (auxiliary) lobes and the width of the main lobe. The width of the diagram is determined in the horizontal and vertical planes at the level of 0.707 of the largest value. Thus, according to this parameter (the width of the main lobe), the diagrams are divided into non-directional and directed. What does this mean? If the main petal knows a narrow shape, then the antenna (decimeter) is directional. The next important parameter is noise immunity. This characteristic primarily depends on the level of the rear and side lobes of the diagram. It is determined by the ratio of the power generated by the antenna under the condition of the coordinated load at the time of receiving the signal from the main direction to the power (with the same load) when receiving from the lateral and reverse directions. First of all, the form of the diagram depends on the number of directors and the design of the antenna.

What does the term "wave channel" mean?

The antennas of this type of TV are very effective directional receivers of radio signals. They are widely used in areas of clearly weak television ether. An antenna (decimeter) type "wave channel" has a large gain and has a good directivity. In addition, these products have a relatively small size, which (along with a high level of amplification) makes it very popular among residents of holiday villages and other settlements remote from the center. This antenna also has a second name - Uda-Yaga (by the name of Japanese inventors, who patented this device).

Principle of operation

An antenna of decimeter type "wave channel" is a set of elements: passive (reflector) and active (vibrator), as well as several directors, which are installed on a common boom. The principle of its operation is as follows. The vibrator has a certain length, it is in the electromagnetic field of the radio signal and resonates at the frequency of the received signal. It induces an electromotive force (EMF). For each passive element, the electromagnetic field acts, which also leads to the emergence of EMF. As a result, they re-emit secondary electromagnetic fields. In turn, these fields induce an additional EMF on the vibrator. Therefore, the dimensions of the passive elements, as well as their distances to the active vibrator, are chosen such that the EMF induced by them due to the secondary fields was in phase with the main EMF, which is induced in it by the primary electromagnetic field. In this case, all EMF are summed up, which provides an increase in the design efficiency compared to a single vibrator. Thus, even a normal indoor antenna of the DMV can provide a stable signal reception.

The reflector (passive element) is installed behind the vibrator 0.15-0.2 λ ₀ . Its length should exceed the length of the active element by 5-15 percent. Such an antenna produces a one-way directional diagram in the vertical and horizontal planes. As a result, reception of reflected signals and fields that come from the back of the antenna is significantly reduced. If it is necessary to receive a television signal at large distances, as well as in difficult conditions, in the presence of a large amount of interference, it is recommended to use a three- and more-element antenna, which consists of an active vibrator, one or more directors and a reflector.

Direct and reflected signals

In an article devoted to the wave receiving device (Tele-Sputnik No. 11 for 1998), it was noted that in the case where the signal source is not a standard (i.e., not a laboratory) oscillator and a radiating antenna, but the signal is broadcast by a television tower, a significant The role is played by weather conditions, as well as the location of the receiver. This especially affects the work of DMV-range products. This is explained by the fact that the wavelength in the decimeter range is lower, respectively, the obfuscation of obstacles is much worse, and any reflection of the signal plays an important role in the quality of the received picture. In particular, even the wall of the house can be a reflector of the waves. So, in the absence of direct visibility, this property can be used - to receive a reflected signal. However, its quality will be lower than that of the direct one. If the level of the broadcast signal is high, but there is no line of sight, then you can use the reflected wave. In fact, the indoor decimeter antenna works on this principle. After all, in a room it is difficult to catch a direct wave if the windows go in the opposite direction. Therefore, if you try, you can always find a point where the received signal will be higher. But in the case of direct visibility, any reflected interference will spoil the received picture.

The technique, allowing to compare the parameters of antennas

In order to test the receiving devices, they need to create the same conditions:

1. Select the installation location in which your antenna will work. You can use the balcony, roof or mast. The main thing is that both the height and the place should be the same for all products.

2. The direction to the source of the transmitted signal should be maintained with an accuracy of three degrees. To do this, you can make a special mark on the mounting pipe.

3. Measurements should be carried out under the same weather conditions.

4. The cable connecting the antenna and the TV must have the same resistance and length. It is best to use one wire, changing only the receivers.

Testing should be carried out only for products of one type. For example, the indoor antenna of the DMV-band should not be compared with the outdoor or with meter receivers. It should be understood that field trials can yield results that will differ materially from laboratory tests.

Decimetre antenna for digital television

Recently, in the media, more and more information is being talked about the need to switch to digital television. Many have already done this, but somebody else is thinking. So far, the signal is broadcast in both modes. However, the quality of analog TV leaves much to be desired. In this connection, people are interested in what decimetre antennas can be used for T2. Let's figure this out. In fact, digital television broadcasts on the channel of the DMV-band. So for its reception the standard DMV-antenna can approach. In stores, you can often see the receiving devices, which indicate that they are designed for digital television. However, this is a marketing move that allows you to sell a standard decimetric antenna more expensive than it costs. Buying such a product, you will not have a guarantee that it will provide a better reception than what is already at your home and has been working for many years. As we said earlier, quality depends mainly on the level of the transmitted signal and the conditions of line of sight. However, it should be borne in mind that in most cities much more powerful generators are used to transmit digital television than for analogue. This is done in order to accelerate the transition to a new standard. After all, viewers want to see a clear image, and not "snow" on the screens. Therefore, if there is a receiver in the window, on which is written "UHF antenna for DVB-T2", know: this does not mean that there is some special product in front of you. Just not quite honest seller wants to cash in on an ignorant buyer. You should also know that the program for the transition to a new standard provides for the establishment of advisory centers. In them you can get exhaustive information on any issue related to digital television. All consultations are free of charge. In some cities, this equipment is in test mode, so the signal may be unstable or weak. Do not worry, the employees of the center will always prompt you how to solve the problem with the quality of the signal reception.

Decimeter antenna with own hands

The length of the DMW waves is within the range of 10 cm to 1 m. This feature has their name. Electromagnetic oscillations at this frequency propagate mainly along a straight line. They almost do not go around the obstacles, only partially reflected by the troposphere. In this regard, long-distance communication in the decimeter range is very difficult. Its radius does not exceed one hundred kilometers. Consider a couple of examples of how to make a decimeter antenna at home.

The first version of the self-made television broadcast receiver will, so to speak, be assembled on its knee from improvised materials. The DMV channels are located on a segment from 300 MHz to 3 GHz. Our task is to make an antenna that will work at these frequencies. For this we need two beer cans with a capacity of 0.5 liters. If you use a larger capacity, the received frequency will decrease. For installation, you need a frame, you can use a board with a width of 10 cm. You can also use a traditional wooden hanger, in which case the received antenna can be hung on a nail in any convenient place in the room. In addition to the frame and cans, it is necessary to prepare a pair of self-tapping screws, tools, coaxial cable, connector, terminals, insulation tape. At one end of the cable, put on the TV connector and solder it. The second end is put into the terminal block. Then attach the screws to the neck of the jars of the terminal. The wires should fit snugly against the metal. Now proceed to assemble the antenna itself. To do this, we fix the banks on the horizontal crossbar with their necks to meet them. The distance between them should be 75 mm. To fix the cans, you can use an insulating tape. Everything, the antenna is ready! Now we need to find a place for a steady reception of a television signal and hang our "hanger" in this place.

Receiver for digital television

This section is intended for people who do not want to use a conventional (analog) product, but want to use a special decimeter antenna for the new format. With his own hands, such a receiver is also collected elementary. For this we will need a square wooden (can be made of plexiglass) frame with a diagonal of 200 mm and a conventional cable RC-75. Presented to your attention the option is a zigzag antenna. It worked well in the digital TV reception range. And it can be used in places where there is no direct visibility to the signal source. If you have a weak broadcast, you can connect an amplifier to it. So, let's get to work. Peel the end of the cable by 20 mm. Next, bend the wire in the form of a square with a diagonal of 175 mm. The end is bent outward at an angle of 45 degrees, the second peeled end is bent to it. Tightly connect the screens. The stripped central core is freely suspended in the air. At the opposite corner of the square, carefully remove the insulation and the screen at a site of 200 mm. This will be the top of our antenna. Now connect the resulting square with the wooden frame. In the lower part, where the two ends are connected, copper braces made of thick wire should be used. This will provide the best electrical contact. That's all, a decimeter antenna for digital television is ready. If it is installed from the outside, you can make a plastic case for it, which will protect the device from rain.