Satellite broadcasts are transmitted by way of transmission waves on very short centimeter frequencies. For this purpose two levels: Ku-band (10.7 to 12.75 GHz), C band (3, 5-4,2 GHz). In terms of electromagnetic wave, having the ability to overcome more than 35 thousand kilometers from the satellite to home antennas, in cable instantly fades away. For frequency conversion in the intermediate, lower, and serve as a satellite LNB. According to the international standards, the range of this frequency is in the range 900-2150 MHz. These frequencies are further taken according to a special cable to the microwave input of the receiver.
Taken to reduce the frequency spectrum of the Converter is inserted into a pair of local oscillators with stabilizers the source of the high frequencies. Reducing the input rate is performed by subtracting from it the local oscillator frequency.
Another caveat is that the satellite signal is received with a small diminishing power. This is unacceptable in tracts receiving devices. In this regard, the second important function of satellite LNB – amplifying of received pulses. It should be noted that the device accumulates not only the useful signal, but coming parallel noise. The device also adds its own background, like any other similar device. In the English interpretation of the converters are referred to as Low Noise Block (LNB) that emphasizes the feature of any device of this type in terms of low noise level.
In the receiving part between the antenna and satellite TV-Converter there are two elements – the polarizer and the radiator. All parts are mounted in a single structure, are located in the focus of the antenna. The purpose of the irradiator – more careful use of the mirror surface and maintaining the marginal gain of the antenna gain. The polarizer serves as a setup to choose the desired type of polarization.
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Pick the considered devices can be as follows:
The first option satellite LNB end with flange of rectangular type, the second model – round element, and the third version – a irradiator.
When Choosing a radiator, you have to consider its shape, which should fit the joints to the antenna used. In addition, you should pay attention to the offset or axial-symmetric type of the receiving element, and the ratio of focal distance to antenna diameter. For offset patterns fit increased from 0.6 to 0.8, while the axial-symmetric it must be of 0.3-0.5. The best option would be to buy the antenna included with the feedhorn that will guarantee their work one hundred percent.
On the choice of LNB of a satellite dish depends on several factors. Chief among these is the frequency range that you plan to use. Mostly European satellites are broadcast in Ku-band. On the same frequency work, some Russian companies.
The Second type of the device – a Converter C-band. These frequencies are designed for professional technique. Some models come with converters combined type. Models that aggregate the Ku-band market abound. It should be noted that the width of this indicator 2,055 GHz. It does not allow synchronous transfer signal to an intermediate frequency. In this regard, it is divided into three streams (GHz):
Satellite converters of the second and third band is focused on taking certain packages.
Most of the converters produced aggregates with a range of type Ku. They are equipped with two local oscillators, which convert the upper and lower ranges. Switch elements by means of a signal transmitted from the receiver via a cable, to the clerk for entering the intermediate frequency from the Converter.
Modern devices, compared with predecessors, have a universal design, band switching is realized by the tonal signal. Universal circular satellite Converter is the number of signals that are used to switch the ranges, and polarization.
Performance local oscillators in such devices have values of from 9.75 to 10.6 GHz. This construction simplifies greatly the setting of the receiver until the auto-configuration after selecting the appropriate menu item.
Those Wishing to take both band, you can suggest a few options. Really set on the antenna a couple of converters with my polarizer and feedhorn. In this case one of the reflectors is slightly out of focus, which will reduce the directional coefficient. This way is quite troublesome.
The Second option – purchase the device type, C/Ku rotor containing both band feed, bisecting the incoming stream of signals. Such elements equipped with the polarizers of the Electromechanicaltype. This design simplifies the installation process, however, has several disadvantages. First, there is a perceptible loss of power of the pulses of Ku-band. Second, there are frequent breakdowns of the moving parts of the rotor, especially at subzero temperatures.
Finally, the third option is the most simple. You just need to install the combined Converter, which has not received special distribution.
This device allows a more efficient use of frequency band of transmitted waves, which doubles the number of broadcast programs. Tuning the frequency of the desired channel, simultaneously exhibit the required polarization. For example, linear satellite LNB polarization in forms of vertical and horizontal waves. Circular generates analog right and left pulses of a circular type.
Polarizer filters waves and flows to the Converter only pulses of one selected polarity. It is worth noting that Russian satellites have a mostly circular action, whereas the European counterparts – a linear system. For reliable reception of circular waves is mounted another item – a depolarizer that converts a circular polarity in a linear direction.
The Discrete polarization changes – this is another parameter of the difference of the polarizers. In universal models, the discrete plane is changed by 90 degrees. There are also electromagnetic device that changes the polarization plane and the variants with the physical movement of the probe. Due to the presence of moving parts, Electromechanical modifications are less reliable and require three control pulses from the receiver, unlike magnetic counterparts, which lack the two signals.
With the advent of digital packages such as "Tricolor” and “compass” has been popular in the European regimen based on the use of the polar antenna and universal Converter. This is due to the high signal quality and digital translation method of the most programs. Phase modulation is very sensitive to transformations that can lead to failures when using magnetic polarizer. In addition, it requires the use of certain materials for the plate depolarizer. As components of the used stamps of the dielectric, designed for use with pulse-type microwave.
If you decide to mount a magnetic polarizer, you will need to purchase an additional Converter with a rectangular flange and the radiator. When the distribution of signal to multiple apartments, optimum use of satellite circular LNB (2 outputs or 4 outputs). They usually have a built-in polarizer (voltage – 13 to 18 In). The type of output pulses, such devices are divided into option with one or two pairs of identical outputs with independent switch and polarization ranges. These devices are suitable for the connection of 2-4 apartments. The second type – with outputs displayed on the vertical and horizontal polarization plus double division ranges in the presence of 4 outputs. These devices are designed for a larger number of subscribers.
This type of device is convenient to operate for those who are planning to limit the reception of the upper or lower range. In this arrangement, one input of the receiver receives a pulse of the horizontal type, and the second – a vertical signal. Analogues of such modifications with four outputs are used in cable networks or for a small group of community reception. In the second case, the reception outputs of the Converter is carried out via the switcher for subsequent wiring on subscribers.
In schemes of collective use must meet higher standards to the gain signal. This value is measured in decibels, the permissible rate in the range of 50-70 dB.
According to user feedback, satellite LNB "Tricolor" it is better to buy with two independent outputs circular polarization 10,7-12,75 GHz noise-0,3 dB. On the market of such devices offers a wide range of manufacturers, from Chinese firms to well-known brands. They differ in price and quality materials, have an identical principle of action.
By Purchasing a Converter for the antenna, pay attention to its design features. Optimum sealed model, otherwise it may be formed in the middle of the device condensation because of the temperature difference. This leads to deterioration of characteristics up to failure. Negative side of this design is the impossibility of disassembly and repair of the Converter. However, the high build quality and innovative materials reduce the possibility of breakage to a minimum.
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