How to watch TV programs without interference. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television antennas

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Let's make a reservation right away that this article does not claim to be a comprehensive scientific study on the problem of combating interference with television reception. It attempts to generalize disparate materials scattered across the Internet, published in journals, scientific papers, and various reference books. Despite such an abundance of information, it is almost impossible for an ordinary viewer to understand what interference is, why they prevent him from watching his favorite programs, and what, in the end, can be done to eliminate them, if not completely, then at least significantly reduce them. Often, articles on this topic are replete with scientific and professional terms, calculation formulas that complicate the understanding of the problem by a person who just wants to "watch your favorite football without interference." We have tried to present the material in an accessible, "popular science" form, avoiding professional difficulties as far as possible.

This article does not describe the organization of reception in specific conditions (long-range, ultra-long-range television reception, other "exotic" options), general concepts and general recommendations are given, which can be successfully applied in almost all cases.

Let's start with terminology

The signal that the television center transmits to us, and which we want to receive on our TV, we will call the main one. Signals that also carry the necessary information, but for various reasons, either late or arrived earlier than the main one, we will call retarded and advanced. Signals that do not carry anything but noise to us, we call noise. Signals, the sources of which are various kinds of non-linear distortions in our television receiver, we will call signals of non-linear distortions. The signals of neighboring television centers, radio stations, which we should not receive, but, however, we sometimes receive, we will call interfering.

"You need to know the enemy by sight"

If you see a second image on your screen that is shifted to the left of the main one, know that you are receiving an early signal! However, this is very rare, since the leading signals appear as a result of your TV receiving the main signal directly, before the same signal reaches the antenna through the drop cable. And since the length of the drop cable for individual reception is generally small, there is practically no difference in the time of arrival of these two signals.

Much more often, a second image appears on the TV screen, shifted to the right from the main one. This means that our TV receives a delayed signal that came later than the main one, either due to multiple reflections from various obstacles on its way from the TV tower to your antenna, or due to reflections between the inconsistent TV input and the antenna output (the signal just “walked” along your drop cable).

Various kinds of "snow", "sparks", "streaks" and "dashes" on the main image, a decrease in its clarity, clicks and hum of the soundtrack indicate that noise interference is being received.

Nonlinear interference will add a "grid" to the screen, moving vertical stripes.

Interfering interference "will give us the opportunity" to receive their signal, and sometimes you can even see the image, hear the sound more often, or listen to the echoes of radio broadcasts in the speakers of your TV.

All of the above is true, but do not forget that theory and practice are not always the same thing. In practice, individual interferences are rarely encountered, much more often one has to deal with their complex, which only complicates the task of dealing with them.

What can be done?

Let's start, perhaps, with the selection of components for our "antenna economy".

It is advisable to select an antenna that has a narrower radiation pattern, pay attention not to the seller's advertising statements, but to the technical characteristics indicated in the passport. At the same time, it will not be superfluous to enlist the advice and recommendations of knowledgeable people. We must pay tribute, now in a store that professionally sells antennas, you really will be provided with the necessary consulting services for free. At the same time, you can trust these tips, because if the sold antenna does not suit you, you can always return it, provided that its presentation is preserved, documents confirming the very fact of purchase (it is better to clarify the return conditions at the time of purchase from the seller in order to save your time and nerves). You need to pay attention to the following parameters: gain, protective action coefficient. Sometimes you can hear this: KUS (KU), KZD. Don't be scared, it's the same! This is the reality - experts love to insert into their speech generally accepted (in their environment, of course) abbreviations and technical terms. Antennas with high CUS and KZD values ​​have greater noise immunity, therefore, improve the quality of the received signal.

Antennas are sold with or without cable. What to buy - you choose. An antenna with a cable will facilitate installation, but not always a high-quality cable is included, and even the length you need. Buying a separate cable is also not a problem now. It is better to dwell on the double-braided version, such a cable has greater noise immunity. And do not select a cable solely from an aesthetic point of view! What looks good doesn't always work well.

In any case, do not neglect the advice of the same experts! Indispensable condition: the cable must be compatible with the antenna output and input of your TV! If 75 ohms are required, then 75 ohms should be.

Now about all sorts of fashionable now sockets. Do you remember the topic of the article? So, if you have a difficult situation, we do not advise you to get involved in them. If you need it and you can’t do without them, purchase only high-quality products, do not chase cheapness. The already "clogged" main signal will receive an additional portion of interference on a low-quality outlet. The rule here is simple. The more connections and devices in the way of the main signal, the more chances to worsen it!

Please note that all connections (cable to antenna, cable and adder / splitter / socket, etc.) must in any case be made with high quality, ensuring reliable contact not only immediately after assembly, but also subsequently, during operation .

Briefly dealt with the components. Now about the place and method of installing the antenna itself. A lot has been written on this issue, so we will give only brief information without going into their scientific justification. A common misconception is that the higher the better. This is far from always the case. Sometimes it is better to put the antenna lower, using an elevator superstructure, for example, which is located on your roof, as a shield in the path of the reflected signal. Or move the antenna closer to the edge of the roof towards the television center, then the surface of the flat roof behind the antenna will somewhat reduce the parasitic effect of delayed signals.

If you are reading this article, then you are not an expert, and you do not have the necessary measuring instruments, so you will have to experiment with the location of the antenna on the roof (both horizontally and vertically). However, this task is not easy! In the city, sometimes it is simply impossible to achieve high-quality reception at a particular antenna installation location. Sometimes it is enough to move a few meters - and a high-quality "picture" will appear on your TV! And sometimes you have to install an antenna on a neighboring house, throwing a cable to your home. In any case, it is possible and necessary to try to organize high-quality reception of television signals! Not a single specialist will tell you with a XNUMX% guarantee that nothing can be done in your case or everything is possible. Almost everything can be done now, though it can cost many times more! We are talking about the use of various filters, attenuators, amplifiers, antenna arrays, finally. Not those arrays that have flooded our market in recent years, but structures of two or more antennas connected into a single receiving device. But this is already a topic for another article, and to do it, and, most importantly, to set it up, a non-professional is not able to do such a design.

Literature

1. Encyclopedia of domestic antennas. Yu. Nosov, A. Kukaev, M., 2001
2. Terrestrial antennas for television reception. I. Sharenkov, TELE-Sputnik N 8(10), 1996
3. Training manual for the training of TV repairmen. L. Vinogradov. M., 1965
4. Reflected television signals in urban environments. V. Kuznetsov, Electrosvyaz No. 4, 1975

Publication: antennaspb.ru

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