Many have probably heard about active home antennas for TV, but do not know what is the difference between them and passive ones? And the difference is that inside there is an amplifier that needs power supply from a 9 or 12 volt adapter. There are other voltage standards, but not the point. The first amplification stage must be set as close as possible to the receiving point, and this greatly increases the sensitivity. Distortion in the feeder (75 ohm wire) in this case almost does not affect the quality.
A special main base of low-noise microcircuits and transistors is selected for the amplifier, but it is not necessary to make it yourself now. The Chinese have already made everything for us long ago. A television antenna with an amplifier is not very expensive, so once and for a long time to get around her attention.
1 General tips for choosing an antenna with an amplifier
- 1.1 Directional pattern
- 1.2 Omnidirectional room tv antenna
- 1.3 Tv Antenna Manufacturers
- 2 Summarizing
General tips for choosing an antenna with an amplifier
Do not forget that the total gain of the active antenna consists of several parts:
- Gainwhich is achieved through the formation of the main lobe of the radiation pattern.
- Conversion factor the amplifier.
With the last point, probably, everything is extremely clear, but about the first one you need to talk in more detail. To begin with, this component can generally be zero. This is the case when your antenna is omnidirectional. They are not often, but also equipped with an amplifier. What are the advantages and disadvantages?
- Has reception from all sidesand, accordingly, there is no need to bother with targeting a television antenna. But at the same time, we also receive interference in the full program, and they also increase and go to the screen.
- Directional antenna has better gain, eliminates unnecessary interference, and at the same time it is more difficult to impose on the target. If the direction of the beam has changed, the broadcast will not be captured.
- Will be able to receive multiple television towers simultaneously... This is so, and all the distorted rays, because of this, the image will begin to divide. There is a similar sign when over-amplifying a signal. What exactly happened in our case is hard to find out.
Attention! What does the radiation pattern mean? The antenna is best taken from one or two directions. This is created - and specifically - by the specifics of its design.
Illustrative example multi-lobe antennas are considered framework. The main thing is to install it perpendicular to the source of the transmission, and which side it is, it makes no difference.
Example unidirectional antenna is a log-periodic and wave channell Everyone probably saw this construction on the roof. It is a large-sized horizontal pin, studded with longitudinal beams, like a mast.
Now consider the form. The directivity pattern is the dependence of the level of signal reception on the azimuth. As a rule, it looks like a parabola, but turned upside down.
It turns out quite a narrow and such a high momentum in the region of zero azimuth. On the edges of it are impulses of different widths and shapes, which are also called side lobes and most often do not participate in the useful receiving of the signal. Ideally, they absolutely should not be.
The best in this plan is considered a parabolic antenna (dish). And the ratio between the height of the main lobe and the initial side lobe is determined in relative values of decibels. The indicator is called the level of the initial side lobe. The higher its negative value, the much better.
The width of the main lobe of the radiation pattern is indicated in degrees relative to 0.707 of the maximum, if field strength is measured. Wherein the area of the whole figure is constantly equal to that even circlewhich is considered an indicator of an omnidirectional antenna. It turns out, according to the law of conservation of energy. As a result, the higher the lobe is (and the amplification factor), the narrower it is, and the harder it will be to catch the signal. Vivid example satellite antenna with its 38 decibels. How hard it is for her to catch a point in the sky. Here, even special devices are designed that estimate the signal level from any device in space. And they are quite expensive!
Omnidirectional room tv antenna
With an omnidirectional antenna is much easier, as we have already said, and the wave channel will be something averaged. Its at least approximately necessary send in the direction of receiving the TV signal. Which indoor antenna best fits where the main lobe is wide or narrow?
We have practically answered this question. When the receiving point is far away, a high gain directional antenna is required. Fine, if this antenna will be activeThis increases the chances of catching a signal. And it will be more difficult to put it on. The selected indoor antenna for an amplifier TV will provide an opportunity to catch weak television broadcasting hundreds of kilometers away. Enthusiasts even tried to make a reception from the Far East and South Africa.
Yes, that's what else needs to be said. There are various rumors about indoor mercury antennas. This is absolute nonsense, or the material that is inside, is not at all mercury.
Just microwave radiation passes only on the surface. Therefore, there is no point in pouring this liquid metal, since, to be honest, its conductivity is so-so in large flasks and to make a device for receiving a signal from this. Wherein mercury vapors are toxicYou can really get a strong poisoning or catch something else instead of television, which then will be difficult to describe with words.
In the end, you can purchase a wireless amplifier for a TV antenna separately, but as a rule, it is much better to buy everything together. But in the first version, we have the ability to design the necessary device independently. Build the amplifier with your own hands is quite difficult. And then it also needs to be customized!
Tv Antenna Manufacturers
Active antennas are manufactured by many companies. From domestic to the ear Delta. We would not say that this is a good or bad company. This is just one of the branches of Russian production, the quality of which is at a completely normal level. We have already described how to choose the right TV antenna, briefly recall that it must be clearly aimed at your tower:
- when it is a radio, then FM or VHF marking (sometimes KV or CB) must be marked;
- when this is a digital TV broadcast, a UHF antenna with reception over 480 MHz is required;
- All-wave antennas, as a rule, are a little more complex, there are also several vibrator mustaches, and a frame, and outdoor antennas will also impress with their original form.
Here are some examples:
- Active all-wave antenna Delta K 331 A has a different amplification factor for the ranges. For HF it is 6 dB, for VHF - 13–14 dB, for a decimeter frequency - 21–24 dB. Thus, the best reception takes place on digital television and regional as well as commercial television channels. To cover such a huge range for MF and UHF, separate wireless amplifiers are used. This gives you the opportunity to get the best quality. The total gain is likely to greatly depend on the directional characteristics of the antenna over ranges. At the meter frequency they are smaller. It is also important that for receiving a radio antenna must be installed on its side, but in this case television broadcasting will disappear. They just have a different polarization. By default, such a television antenna does not accept a radio signal. Naturally, the device is designed to use a standard wire with a wave resistance of 75 Ohms.
- The active television antenna Delta K 331 A.03 even in the directory is not called active. Although its function is clearly better than the previous one. Such a log-periodic antenna costs about 1000 rubles. The previous product belonged to the same class, but the type of vibrators looked like a wave channel. And in this model, they are in the form of triangles that are in their own order. For the range of MV installed telescopic "antennae." These two types of wireless antennas are indoor models. This means that if you put them on the roof, the device will fail due to the destruction of external conditions and incorrect operating conditions of the electrical internals valid. The main advantage in this case is that the “antennae” is oriented regardless of vibrators, and accordingly, you can receive broadcasting from two directions, or only from one tower. This is as you like. In addition, the oscillators of a log-periodic antenna can be adjusted by elevation (set down or up). It is designed to create a reception in difficult conditions of the city, when the signal can go from different directions.
- External television antenna H 3311 A made on a log-periodic scheme, but the antennae for the frequencies of MW it is fixed tightly. And this is quite logical. On the mast, the device will begin to sway strongly in the wind, therefore it is impossible for the broadcasting to go astray. It is indicated that this is a combined device of two, a symmetrical vibrator and a log-periodic scheme, but we tend to think that this is a fairly simple description. We would say that we are on HF and VHF, and a pair of log-periodic devices for UHF, going on two cross-arms parallel to each other.
Manufacturers of home antennas for televisions are trying hard. In particular, they include broadcasting reception, but soon it will still go to the multiplex. Therefore, to buy antennas without receiving the SCM is currently unfashionable. However, broadcasting in digital format is promised on the HF and HF frequencies, let's see what happens after.
Manufacturers of antenna amplifiers are usually the same. In particular, there is a market and Delta. The advantages of a separate acquisition, we have already considered above. In this case, a situation may arise when the signal MW will not need to be amplified, as it relates to local television broadcasting, and the UHF is received from afar. In this case, a broadband device is not required, but it may be necessary to have a pair of tees in order to complete the isolation.