Satellite broadcasts are transmitted by the method of transmitting waves at very short centimeter frequencies. For this purpose, two levels are used: Ku-band (from 10.7 to 12.75 GHz), C-band (3.5-4.2 GHz). At such values, the electromagnetic wave, which has the ability to overcome more than 35 thousand kilometers from the satellite to the home antenna, instantly fades in the cable. It is to convert the frequency to an intermediate, lower indicator that satellite converters serve. According to international standards, the spectrum of this frequency is in the range of 900-2150 MHz. These frequencies are then fed through a special cable to the microwave input of the receiver.
General principle of operation
To reduce the received frequency spectrum, a pair of local oscillators with high-frequency source stabilizers are built into the converter. The input indicator is reduced by subtracting the local oscillator frequency from it.
Another nuance is that the signal from the satellite comes with a low fading power. This is unacceptable in receiver paths. In this regard, the second important function of satellite converters is the amplification of received pulses. It should be noted that the device accumulates not only a useful signal, but alsoincoming parallel noise. Also, the device adds its own background, like any other similar device. In the English interpretation, converters are referred to as Low Noise Block (LNB), which emphasizes the peculiarity of any device of this type in terms of low noise level.
Device and equipment
In the receiving part between the antenna and the satellite TV converter there are two more elements - a polarizer and a feed. All parts are mounted in a single structure, located at the focus of the antenna device. The purpose of the feed is to make more careful use of the mirror surface and maintain the maximum gain of the antenna gain. The polarizer serves as a setting for selecting the desired type of polarization.
The equipment of the considered devices may be as follows:
- Issue of converters separately.
- Models with built-in polarizer.
- Design that combines an offset irradiator and a polarizer.
In the first version, the satellite converter ends with a rectangular type flange, the second model - with a round element, and the third version - with a feed.
When choosing a irradiator, it is necessary to take into account its shape, which should fit at the joints to the antenna used. In addition, attention should be paid to the offset or direct-focus type of the receiving element, as well as the ratio of the focal length to the diameter of the antenna. For offset models, an indicator from 0.6 to 0.8 is suitable, while for direct-focus models it should be 0.3-0.5. The best option would be to buy an antenna complete with a feed, which will guarantee their compatibility one hundred percent.
Selection criteria
The choice of a satellite dish converter is influenced by several factors. The main one is the frequency range that is planned to be used. European satellites predominantly broadcast in the Ku band. Some Russian companies operate on the same frequencies.
The second type of device is a C-band converter. These frequencies are geared towards professional reception. Some models are available with combined type converters. There are plenty of models aggregating with Ku-bands on the market. It should be noted that the width of this indicator is 2.055 GHz. It does not make it possible to synchronously transfer the signal to an intermediate frequency. In this regard, it is divided into three streams (GHz):
- FSS - 10, 7 - 11, 8.
- DBS - 11, 8 - 12, 5.
- Telecom - 12.5 - 12.75.
Satellite converters of the second and third bands are focused on receiving certain packets.
Universal modifications
Most of the manufactured converters aggregate with Ku-type range. They are equipped with two local oscillators that convert the upper and lower ranges. The elements are switched by means of a signal that is broadcast from the receiver via a cable that serves to receive an intermediate frequency from the converter.
Modern devices, compared to their predecessors, have a universal design, range switchingthey are carried out by means of a tone signal. The universal circular satellite converter differs in the number of signals used for switching bands and polarization.
Indicators of local oscillators in such devices have values from 9.75 to 10.6 GHz. This design greatly simplifies the receiver setup, up to automatic configuration after selecting the appropriate menu item.
Satellite LNBs for Tricolor
Those who want to take both ranges at once, we can advise several options. It is realistic to install a pair of converters on the antenna with its own polarizer and feed. In this case, one of the feeds will be slightly out of focus, which will reduce the directional gain. This path is considered quite troublesome.
Second option is to buy a C/Ku rotor device containing both range feeds, bifurcating the incoming signal stream. Such elements are equipped with electromechanical type polarizers. This design simplifies the installation process, but has several disadvantages. Firstly, there are tangible power losses in the Ku band pulses. Secondly, there are frequent breakdowns of the moving parts of the rotor, especially at sub-zero temperatures.
Finally, the third option is considered the easiest. You just need to install a combined converter, which has not yet received much distribution.
Polarizer
This device makes more efficient use of the frequency range of transmitted waves, doubling the number ofbroadcast programs. By tuning the frequency of the desired channel, the required polarization is synchronously set. For example, a linear satellite converter generates vertical and horizontal waves during polarization. Circular analog generates right and left circular type pulses.
The polarizer filters the waves and passes only pulses of one selected polarity to the converter. It should be noted that Russian satellites have a predominantly circular action, while European counterparts have a linear system. For confident reception of circular waves, another element is mounted - a depolarizer that transforms circular polarity into a linear direction.
Discreteness of polarization change is another parameter of difference between polarizers. In universal models, the plane discretely changes by 90 degrees. There are also electromagnetic devices that smoothly change the plane of polarization and options with mechanical 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 analogues, which require two signals.
Phase modulation
With the advent of digital packages such as "Tricolor" and "NTV Plus", the European reception scheme based on the use of a polar antenna and a universal converter gained popularity. This is due to the high quality of the signal and the digital method of broadcasting most programs. Phase modulation is very sensitive to transformations, which canlead to malfunctions when using a magnetic polarizer. In addition, it requires the use of certain materials for the depolarizer plate. Dielectric grades are used as components, designed to work with microwave type pulses.
If you decide to mount a magnetic polarizer, you will need to additionally purchase a converter with a rectangular flange and an irradiator. When distributing the signal to several apartments, it is optimal to use a satellite circular converter (2 outputs or 4 outputs). Usually they are equipped with a built-in polarizer (voltage - 13-18 V). According to the type of output pulses, such devices are divided into versions with one or two pairs of identical outputs with independent switching of polarization and ranges. Such devices are suitable for connecting 2-4 apartments. The second type - with outputs output by vertical and horizontal polarization plus double division of the ranges in the presence of 4 outputs. These devices are designed for a larger number of subscribers.
Two-pin converters
This type of device is convenient to operate for those who plan to limit themselves to receiving the upper or lower range. With such a scheme, a horizontal type pulse enters one input of the receiver, and a vertical signal enters the second. Analogues of this modification with four outputs are used in cable networks or for organizing a small collective reception. In the second case, reception from the outputs of the converter is carried out through switches for subsequent wiring to subscribers.
Community circuits have higher standards for signal gain. This value is measured in decibels, its permissible indicator varies between 50-70 dB.
Reviews
According to user feedback, it is better to purchase a Tricolor TV satellite converter with two independent outputs, circular polarization 10.7-12.75 GHz, noise level 0.3 dB. On the market, such devices are offered by many manufacturers: from Chinese firms to well-known brands. They differ from each other in price and quality of materials, have an identical principle of operation.
Finally
When purchasing an antenna converter, pay attention to its design features. A sealed model is considered optimal, otherwise condensation may form in the middle of the device due to temperature differences. This leads to a deterioration in performance, up to failure. The negative aspects of this design include the impossibility of disassembling and repairing the converter. However, high build quality and innovative materials keep the possibility of breakage to a minimum.
