Frame antennas, half-wave vibrators, symmetrical and asymmetrical, subspecies of the above mentioned ones - zigzag are traditionally used in the room."Cheburashka" from an aluminum sheet with rings-ears at the edges are unpopular today, they require too much effort to manufacture, and costs increase. Device designs are typical. Log-periodic antennas are made for the upper range of UHF, and also wave channels are in use. How to choose how a room TV antenna is constructed from a variety of options - see the answer below.
What kind of indoor antenna to choose
A room antenna can be made of wire and improvised materials. Home-made indoor antenna is good because it is cheap and finely tuned to the desired frequency. Thick walls will not stop reception. And now about the manufacture of indoor antennas.
Just half an hour going to half-wave vibrator. And for the manufacture of suitable wire, beer cans. The choice is chic, if you understand what you are doing. First of all, let's talk about polarization:
- Horizontal linear polarization is adopted in television: it is better caught by direct conductor systems. Depending on the type of antenna, there may be an infinite number of them. Longer have to work on log-periodic varieties and wave channels. Consist of a set of directors and an active vibrator, more precisely, this is true for the latter case. The complexity of the log-periodic antennas is simply amazing, the transverse conductors are powered by a two-wire line and are in antiphase. We believe that the log-periodic antenna is capable of becoming the choice of an experienced designer, and coordination is a completely separate topic.
- Vertical linear polarization is used in broadcasting. For its reception, the types of antennas described above are applicable, but nuances are noticed. First, the devices will have to be rotated 90 degrees along the axis, laying on its side so that the whiskers become vertical. In hybrid antenna "whiskers" rotate on hinges, it is allowed to adjust as you like. Secondly, if the wave impedance of 75 ohms reigns in television, 50, 200, 300 ohms are present in the radio and communications, except for this. The antenna for reception is coordinated as necessary, otherwise a part of the power will be reflected, doubling of the signal, echo is possible. The situation is complicated by the fact that at waves below 100 MHz, and these are VHF, HC, MW, DV and 34 MHz radio stations, it is necessary to balance the signal, since the cable is an asymmetrical line. For this purpose, for example, U-bends are used.
Now readers understand that it is difficult to create a universal antenna, since the segments( in the simplest case of television and radio) will work as a separate structure, and both must be correctly combined. For example, it is possible to do this through a two-wire feeder of the required length, whose resistance for some waves is high, and for others it is small. Moreover, the signal is taken in a certain place from the already specified condition. It is clear that an ordinary person will not be able to solve such a problem, it is necessary to copy ready-made drawings.
A noteworthy construction called a patch. This site, traditionally square, has 4 or more square radiators on it. This design appears at relatively high frequencies and is used in cellular communications and WiFi. For a simple reason: for the frequencies of 400 MHz, the size of the pads is significant, which is not pleasant to the ordinary man in the street.
And now I would like to share a nomogram for determining the wave cable. This is important if the line is found in bins and is not purchased. A nomogram will help readers determine an essential parameter with a caliper and ruler. Let's make a reservation that the coaxial cable consists of a conductor, internal insulation, shield-braid and external insulation. The type of dielectric of internal insulation, the diameters of the core and the screen is considered important. Coaxial cable is made of copper. This information is enough to find the necessary parameters by the picture. The nomogram was located on the forum.
Please note that the type of dielectric rather depends on the ratio of the diameters of the central core and the screen. From the nomogram we find the wave resistance. Since standard cables are spaced at a significant distance, we believe that there will be no difficulty in finding resistance. Some of the characteristics can be found on the Internet, probably, on the outer insulation of the cable or elsewhere there will be visible signs. An important parameter is weakening in the coaxial, but if you need to pull away( 5 meters or more).For a room antenna, this is irrelevant.
We agree that the impedance of the receiver is determined by the passport, for example, the TV will be 75 Ohms. As for the other technology, the variety is amazing. What to do if the wave impedances of the receiver and the antenna do not match. Take the trouble to find a suitable type of cable, then the construction of matching devices begins. These include the above U-knee, quarter-wave transformer and others. You should not be afraid - the designs are made according to calculated sizes from one or several types of coaxial cable.
How to make an indoor antenna
Readers were convinced that there was no difficulty in the selection process. We point out that wave channels and log-periodic antennas are designed to search for a wide range. Hardly a similar goal is to lovers of digital television, for them half-wave vibrators are ideal. As for log-periodic antennas, do not look for special methods of calculation: there is no exact today. Feel free to copy the finished design from the Internet of the desired range, or then charge yourself when setting up. Log-periodic antennas refer to the form where it is realistic to obtain a zero effect from the use of the structure. Adjustment is carried out by changing the distance between the two supply lines, and the location of the closing jumper behind the screen. This changes the characteristic impedance.
As for the antennas of the wave channel type, there are a lot of benefits to create, but we recommend choosing ready-made structures, especially since the calculation example has already been given on the site. According to the special tables and channel number, the necessary characteristics are selected.
Half-wave vibrators are easier to construct. The length of both arms is half the wavelength. The ideal dipole has a resistance of 75 ohms, which is especially good for the television range. The radio can be caught on a quarter-wave vibrator( but vertical), either symmetrical( like a television) or unbalanced( a vertical pin sticking out of the receiver).In this case, the antenna impedance is 50 ohms. If you use a similar solution for 75 Ohm hardware, a part of the signal is lost.
A nice article on the topic of quarter-wave transformers of coaxial lines at http: //www.ngpedia.ru/ id522653p1.html.
As for the general theory, then: a quarter-wave transformer is a segment of a line with a quarter-wave length. Its characteristic impedance is equal to the square root of the products of matched resistances.
The calculation of an atypical coaxial( you can check by the nomogram) is located here http: //ra6foo.qrz.ru/ transfor.html. In the presence of all the data for the design. Please note that in the above calculator there are two dielectric layers. If you take a single, then put one value of the dielectric constant, and divide the diameter into two derived boundaries. Now readers can make their own indoor antenna and properly align.
There are enough examples of coaxial cables in the network, we suggest turning your attention to the figure presented above taken from the site vunivere.ru/work8182, where an example is given for the calculation of a two-wire line with an air dielectric. The dielectric constant of the air is found in the directory, usually it is a unit. Other data is shown in the figure. Thanks to them, we can calculate the characteristic impedance of the W lines by the formula specified here. For the feeder and transformer, this will be, respectively, 227.4 and 144.3 ohms. The wavelength for which the design is designed is easy to determine by multiplying 0.15 meters by 4. Accordingly, the frequency is 500 MHz. This is a live example of line matching( 227.4 ohms) and antenna( 114.3 ohms).The conditions for lossless power transmission are determined by the diameters of the copper cores of the line and the transformer.
Indoor TV antenna, assembled from the material at hand and properly matched, will serve faithfully and reliably.