Offset antenna - the best TV channels in excellent quality
The benefits that a satellite dish brings to its owner have led to the great popularity of satellite television. After all, thanks to the widest selection of channels, you can not only get access to a huge number of films, favorite sports and cultural programs, but also keep abreast of all important events, improve your knowledge of a foreign language, that is, combine a pleasant pastime with useful self-education. And if we add here the excellent quality of image and sound, it becomes clear why a satellite dish is of such interest to those who are just wondering what kind of TV to install in a new apartment or who are tired of constant interference when receiving a signal.
How does a satellite dish work?
The operating principle of all plates is approximately the same. First, the signal hits the mirror surface. Then it is reflected and sent to the converter, from where it in turn reaches the receiver, and from it it is sent directly to the TV itself.
A satellite dish can be one of two types: offset or direct focus. is not directed exactly to the satellite, but slightly below it, since the signal that is reflected from its surface enters the converter at a certain angle. This type of receiving device is mounted almost vertically, which avoids the accumulation of factors that greatly degrade the quality of reception. This is the type of antenna that can most often be seen near the windows of apartment buildings, since it is convenient to install along the walls. The optimal size of this plate is 1.5-1.8 m.
In a direct-focus device, part of the mirror surface is covered by a converter, but as the diagonal increases, this becomes less noticeable. The quality of reception directly depends on the size. Good characteristics start from 1.5 m. With such dish sizes, the feed source no longer “shades” the surface of the mirror. This type of antenna is used for professional reception.
It should be noted that the satellite dish is very “picky” about the terrain. Any interference in the signal path, be it a tree or a wall, can completely or partially block the reception. Therefore, before a possible purchase, you need to check whether there is interference in the direction from the intended installation location to the selected satellite.
Satellite Is it worth a try?
If you type “homemade satellite dish” into a Google search, the Internet will bring up the most bizarre pictures with images of such amazing designs that sometimes you admire the boundless imagination of a person. There are beer cans, umbrellas, cut-up frames, etc. Will any of this work? Maybe. However, it is unlikely that such a design can compare with a regular plate, which can be easily purchased at any specialized store. Considering the fact that the average price of satellite dishes is quite affordable, there is no need to waste your time on the construction of a dubious design, except, perhaps, if the person is an inventor by nature or has deep knowledge in this field.
Before choosing a satellite antenna (dish), you need to get an idea of how it works. In principle, the operation of the plate is not complicated. The antenna itself, the dish in our understanding, is a reflector of electromagnetic waves, like an ordinary mirror, which it focuses on a converter rigidly mounted on the dish. The converter converts the signal received from the satellite into the first intermediate frequency and transmits it to the receiver via cable. The set, consisting of a reflector, a converter, is the receiving antenna itself.
Antennas according to their design are divided into two main types - direct focus (round) and offset (elliptical).
Satellite signals are broadcast mainly in the Ku bands (~11 GHz) and less often in the C bands (~4 GHz), that is, the signals have a wavelength of 27 and 75 mm, respectively.
All Russian satellite television operators: NTV plus, Tricolor TV, Continent TV, Raduga TV, etc. operate in the Ku (~11 GHz) band!
Satellite dish parameters
Effective antenna area A(effective antenna surface) - a value that characterizes the ability of a receiving antenna to concentrate electromagnetic radiation incident on it. A is defined as the ratio of the maximum power that can be delivered by the receiving antenna (without loss) to the matched load to the power P, plane wave (not distorted by the antenna) per unit area of the antenna.Antenna noise temperature. Noise increases the threshold for digital devices to respond to a useful signal. The antennas themselves do not make noise; the noise is created by the surface of the earth, the structures on it, the airwaves, and deep and near space. Obviously, for a given antenna size, the noise will be less for antennas with a narrow radiation pattern and small side lobes.
The receiving and transmitting antennas use the same principle of operation, because In almost any linear systems, the field conversion coefficients are mutual. However, the technical and operational features of receiving and transmitting antennas may differ significantly due to differences in the requirements placed on them (power limits, frequency bandwidth, noise, etc.).
Selecting a satellite dish
How to choose an antenna by size. When choosing an antenna, a very important parameter is its size. The size is directly related to the gain of the dish, the larger the size, the higher the gain. If the size of the dish is smaller than that allowed for receiving the required transponder, then the message “no signal” will appear on the TV screen; if we have a threshold signal level, then the image will crumble into squares, the same will happen if the dish is not accurately aligned to the satellite and when the satellite signal is shielded foreign objects.
For different satellite signal powers, different dish diameters are required: 53dbW - 0.6m, 48dbW - 0.8m, 45dbW - 1.0m, 40dbW - 1.5m.
Usually installers know what size dish can be used to “catch” the desired satellite; we will tell you how to determine the required dish size yourself at the end of the article.
How to choose an antenna by type. Next you need to decide on the type of antenna: direct focus (round) or offset (elliptical)?
Up to a size of 1.6m, for domestic needs in the Ku (~11 GHz) range, offset antennas are mainly used, why?
It follows from the figure that the converter and its mounting hardware create a radio shadow on the dish, which reduces the efficiency of signal reception. In addition, during precipitation, water accumulates in the dish, especially at a high elevation angle, closer to the equator, as well as snow, which also reduces the efficiency of satellite signal reception.
Already for satellite antennas with a size of 1.5 m, the radio shadow from the converter and its mounting is a relatively small part of the mirror area to be taken into account. A round direct-focus antenna focuses radio waves more evenly on the converter feed. In addition, for a round antenna it is easier to calculate and coordinate the converter feed with the antenna, due to which the entire surface of the antenna is effectively used. With an offset plate, up to 10% of the area is not used due to its shape, especially for large plates.
For these reasons, antennas larger than 1.5 m in size are manufactured mainly as direct focus antennas and are intended for professional reception.
Offset antenna - with a shifted focus, has the shape of an ellipse, elongated vertically. The converter is mounted on a special bracket; due to the shifted focus of the antenna, the converter and its mounting unit do not fall into the irradiation zone. The reception efficiency of such an antenna is higher than that of a direct-focus antenna. The plane of such antennas is located almost perpendicular to the plane of the earth and precipitation does not accumulate on its surface. The mounting design of an offset antenna is simpler than that of a round antenna and its cost is lower. Choosing an offset antenna!
How to choose an antenna based on design, material and stamping quality. Antennas vary in designs- solid (one-piece stamped), mesh and prefabricated (sectional). Solid antennas are preferred as they provide better reception quality. Mesh plates, for example Lance, have a reduced windage, but their reception efficiency is lower than that of solid ones. Some believe that the holes in the mesh themselves reduce the efficiency of the antenna, that the signal “leaks” through them. In fact, the holes have nothing to do with it. The fact is that the mesh is soft and in the spaces between the stiffening elements of the plate it is stretched, trying to take a flat shape, as a result of which the surface of the mesh plate is not a paraboloid, but consists of flat segments, forming a surface close to a paraboloid. The antenna paraboloid is considered smooth if the average size of the irregularities on the surface of the dish does not exceed one quarter of the wavelength. In the Ku range, the length is 2.5 cm, while the permissible deviation of the surface from the paraboloid will be approximately 6 mm. In the C band, the wavelength is 7.5 cm, and the size of the irregularities can therefore reach 19 mm.
Because of this, in the C-band, to lighten the weight, antennas are made of mesh, and to reduce dimensions during transportation, they are made of petals, because C-band antennas are usually larger than 1.6m. Material
, from which the antenna mirror is made, can also be different: plastic, due to the poor quality of antennas, due to warping in the sun, is practically not used, steel is a durable material, therefore it ensures good quality of the mirror, but the dishes are heavy and susceptible to corrosion, aluminum - the material is light but soft, subject to deformation and does not rust., is directly related to the antenna gain. The quality can be easily checked by placing the antenna on thick glass; if the quality is good, the dish will fit snugly around the entire circumference of the glass. The warping of the antenna with a “screw” has a particularly bad effect on the antenna gain.
How to choose an antenna based on the type of suspension. There are antennas with azimuthal and polar suspensions. With an azimuth mounting, the antenna is aligned to the satellite and is rigidly mounted on the bracket. Polar - suspension rotating with a special actuator. Using a polar gimbal, you can tune in to all satellites “visible” in the given geographic coordinates.
The polar suspension is designed in such a way that, by rotating around a vertical axis (i.e. changing the azimuth of the setting to the satellites), the antenna also tracks the elevation angle, that is, it describes the arc on which the satellites are located.
For household antennas, polar suspensions are no longer relevant; they have been replaced by motorized suspensions; conventional antennas with azimuthal suspension are hung on them.
Mirrors of different depths: 1- shallow (long-focus); 2 - average in depth (mid-focus);
3 - deep (short throw)
The radiation pattern of a parabolic antenna is completely determined by the field distribution in its aperture, as well as the relationship between the wavelength and the radius of the mirror aperture.
At a certain value of the antenna mirror aperture, the main lobe of the radiation pattern will be the narrowest if the distribution of the field amplitude in the mirror aperture is uniform, but in this case the side lobes will also be large. If the field amplitude decreases from the center to the edges of the mirror, then the main lobe of the radiation pattern becomes wider and the levels of the side lobes decrease.
To reduce the level of side lobes, the antenna mirror is irradiated in such a way that the field amplitude decreases when moving from the center of the aperture to its edges, but at the same time the coefficient of utilization of the aperture surface also decreases. In practice, a compromise solution is sought for rational irradiation of the mirror.
If one strives to obtain the highest gain from a parabolic antenna, then the mirror is irradiated in such a way that the field amplitude at its edges is 10 dB lower than in the center of the aperture.
By selecting the feed, the size of the paraboloid and the focal length, the required radiation pattern of the satellite antenna is obtained. The radiation patterns of antennas of different mirror depths are also different, because they have different distributions of field amplitudes in the mirror aperture. Less deep mirrors are irradiated more evenly, so their main lobe is narrower and the side lobes are larger. You can obtain a given amplitude distribution in the antenna aperture in various ways:
- Selecting an irradiator.
- Using two-mirror antennas.
- The shape of the mirror and its modifications.
In conclusion, we give advice, how to choose your plate size. The smartest thing to do is look at the coverage map of the desired satellite and determine from the irradiation power what minimum antenna diameter is required.
For example, on the sites http://www.flysat.com or http://www.lyngsat.com.
How to choose an antenna (dish) for Russian satellite operators
Based on the above information when considering satellite irradiation zones, you can choose the size of the satellite dish for viewing TV channels of each of the Russian satellite operators. The irradiation zones and the distribution power of the satellite signal in the irradiation zones can be viewed on the website pages:
Transponders and irradiation zone of Tricolor TV >>
Transponders and irradiation zone NTV Plus >>
Transponders and irradiation zone Continent TV (Telecard) >>
Modern information transmission technologies have advanced so far that traditional analogue television is becoming a thing of the past, giving way to satellite television. And this is not surprising, since satellite television is based on digital technologies that allow you to enjoy the excellent quality of numerous channels. At the same time, it is satellite broadcasting that appeals to both adults and children, because each of them will find something of their own among the abundance of programs and films. And high-definition satellite television can easily make a cozy sofa in front of the TV a favorite place for the whole family to relax.
Among the numerous types and types of satellite antennas for receiving a large number of channels, it is customary to use two main models related to parabolic antennas: offset (asymmetric) and direct focus (symmetric). The most common in private reception of satellite television is offset satellite dish, which is an asymmetrical cutout from a paraboloid of revolution with a special irradiator at the focus of the paraboloid itself. When viewed through light, the offset antenna looks like a vertically elongated ellipse. The useful area of the antenna is not obscured by either the feed or its supports due to the fact that the focus of the segment is located below the geometric center of the offset antenna. While the converter and fastening spokes of the direct-focus antenna obscure a certain part of the reflective surface of the mirror, which cannot but affect the utilization rate of the mirror surface.
The stability of the offset antenna under wind loads is increased due to the location of the feed, which is installed below the center of gravity of the parabolic antenna. This feature should be taken into account when setting up the antenna, taking into account the fact that with offset antennas the satellite is above the perpendicular to the plane of the antenna itself by a certain angle. When installing the antenna, the mirror should be mounted almost vertically. The angle of inclination may vary only slightly due to the characteristics of geographic latitude. This vertical position completely eliminates the accumulation of moisture or snow in the antenna bowl, the presence of which can negatively affect the quality of reception. This is another difference between an offset antenna and a direct-focus antenna. In the latter, increased sealing is not used, since moisture ingress does not pose a particular threat. But the offset antenna must be carefully treated with sealant, otherwise the signal quality will deteriorate at the slightest ingress of moisture.
The most common material for making offset antennas is aluminum. It is lighter in weight than steel and does not corrode, but a significant drawback is the softness of the material. If not handled very carefully, the aluminum antenna can easily become deformed, which will negatively affect its performance. When purchasing such an antenna, you should pay attention to surface distortion and possible defects that will impair the performance of the device.
If you choose a steel antenna, you should not forget about possible corrosion. When purchasing a steel mirror, you need to pay attention to the quality of its coloring. Despite their lightness, plastic mirrors are bad because snow instantly sticks to them, and over time they become severely deformed due to exposure to ultraviolet radiation or temperature changes.
When purchasing a dish, special attention should be paid to the elements of the bracket on which the antenna will be mounted and the suspension, carefully checking their reliability. It is also necessary to inspect the fasteners, especially if you plan to install the antenna in a windy or high place. The bracket is secured using self-wedging bolts. In this case, the size of the bracket itself is of great importance: the design should allow the installed antenna to be directed in the desired direction, but in no case should it rest against the wall with the edge of the mirror.
It should be noted that, according to the “quality - price" offset satellite dish matches as much as possible. Its cost ranges from 100 to 700 USD. depending on the size and material of the antenna. The only question you need to decide before purchasing is which satellite the antenna will be tuned to. Since the diameter of the offset antenna directly depends on the selected operator. Basically, these are dishes with a diameter of 0.6 to 0.9 m, but to view foreign channels you will need an antenna with a diameter of over 1.2 meters.
When setting up a satellite dish, you need to take into account offset antenna angle, which is the angle between the electrical and geometric axes of the antenna. For direct-focus antennas it is zero, and for offset antennas it is approximately 20 to 28 degrees. The value of the offset angle does not have a particular impact on the quality of the antenna, but its value should be taken into account when tuning. Setting up the offset antenna in the vertical plane consists of installing the reflector at an angle that will be equal to the difference between the satellite elevation angle and the offset angle.
You must be aware that installing an offset antenna is a very complex and labor-intensive process, the timely and high-quality completion of which can only be accomplished by an experienced specialist in this matter. He will select the most optimal place to install the antenna and securely mount all satellite equipment, tuning all the channels received by the antenna. The client will only need to select and purchase an antenna; leave everything else to the professionals.
People who are faced with choosing a satellite dish for the first time, first of all, pay attention to its size. And this is correct, but there are still many factors that need to be correctly assessed. This is the shape, the material of manufacture, there are also perforated plates, mirror plates and many other different designs, the variety of which can make your head spin. In addition, when choosing a plate, you need to decide on the following properties:
Satellite reception area;
What channels are you interested in;
Is it possible to tune in to the satellite: are nearby buildings and other objects interfering?;
A dish is selected for one satellite or for several;
Economic component.
Direct focus
The task of a satellite dish is to collect and focus the signal to one point. With a direct focus, the beam is focused directly in the center, it is immediately tuned exactly to the satellite. The focus is where the converter is mounted on metal rods. Both the converter and the holders cast a shadow on the mirror, reducing the useful coefficient of the reflective surface. Therefore, plates of this type are more effective with large diameters - from 130 cm.
In addition, when setting a direct focus dish, the degree from the horizon can be up to 20%, so snow ice, water, leaves, and dirt may remain in the bowl, which settle on the reflector and also significantly impair the reception of codes. Direct focus is preferred if you plan to receive signals from distant satellites.
Offset
With the offset one, the focusing center is slightly shifted downwards and it is installed almost vertically. It cannot boast the same signal quality as a direct focus, but it picks up well with a small diameter of up to 150 cm, is easier to install and does not need to be cleaned. Therefore, it is better suited for household use.
Satellite, 2-mirror, toroidal multifocal dish
Satellite, 2-mirror, toroidal multifocal dish allows you to simultaneously receive signals from 16 satellites. This is a great alternative to a motorcycle suspension. In addition to the elevation angle and azimuth, this antenna also adjusts the tilt of the mirror, depending on the geolocation of the reception and the satellites you are going to target. The antenna catches the signal in the sector of 40-60 degrees.
The most important thing when buying such a plate is to distinguish the original from the fake. Indirectly, this can be done by weight and quality of the metal. Counterfeits are made from thinner metal, which does not hold the geometry of the plate well.
You can also pay attention to the prefabricated petal plate. It is more convenient for transportation and is suitable if you install the plate in the garden for the summer, and when the season ends, you take it to the city. Its only drawback is its fragility, so it must be handled very carefully.
Solid or perforated
Antennas are perforated only to reduce windage and weight. This is important if the equipment is installed on a mast. A gust of wind can give a load of up to 200 kg and the perforated mirror is guaranteed to withstand it. Perforation does not in any way affect the quality of the signal, which is reflected exactly the same from both the perforated and solid surfaces. Such devices are imported from abroad, so they are more expensive than usual.
Selecting a suspension type
This is another important parameter when choosing an antenna. A simple and cheap azimuth suspension allows you to rigidly tune the equipment to a specific satellite. To catch a signal from another, you will have to completely reconfigure it.
The more complex and expensive polar harness is customizable. It allows you to set up a dish for several satellites in different orbits.
Material of manufacture
Satellite dishes can be found in aluminum, steel and plastic. Aluminum plates are quite expensive and, of course, superior to others in many respects, including corrosion resistance. However, they are more susceptible to deformation due to the softness of the metal. Deformation of the plate can greatly impair the quality of its reception. Most often, aluminum dishes are used for mounting on a motorized suspension with quick switching between channels from different satellites. Thanks to its light weight, it places less stress on the gears.
If you increase the size of a steel dish, it will receive a signal at the same level as an aluminum one, cost 3 times less and will last at least 10 years. However, such a plate is heavier and is susceptible to corrosion if there are coating defects.
Plastic plates are more fragile, especially in winter, and are susceptible to deformation under the influence of sunlight and temperature changes. Although, the more stiffening ribs on the plate, the more durable it is. Snow also sticks to them. Therefore they are not particularly popular.
Thus, inexpensive and functional steel plates are in greater demand. However, there is no argument against buying aluminum plates, if financial resources allow.
Size is the main thing!!!
Size is the determining parameter. It is for this situation that the definition is suitable: the more, the better. The difference in signal reception between a 55 cm and a 90 cm dish will be very noticeable. There are no clear recommendations for what size antenna to buy. When choosing, the principle of practical rationality should work. It is only necessary to take into account additional tolerance if there is a desire to reconfigure the equipment for another satellite. The tolerance should not be large so as not to overpay for extra centimeters.
The choice of diameter depends on the signal strength level in your region. It is determined by the coverage map of each specific satellite. In other words, the choice of satellite dish diameter directly depends on the location of the buyer. Don't forget to allow for weather conditions. Large satellite television operators supply their dealer centers with sets of equipment with already calculated mirror diameters for a specific area.
It is believed that to set up for more than one satellite, the optimal diameter of the dish should be 120 cm; for one satellite, 90 cm is enough.
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