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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Digital satellite TV. History of invention and production
Directory / The history of technology, technology, objects around us Satellite television - a system for transmitting a television signal from a transmitting center to a consumer, using as a repeater artificial Earth satellites located in space in geostationary (previously and in other types of orbits) near-Earth orbit above the equator, and equipped with transceiver equipment. Compared to over-the-air terrestrial television, it provides high-quality television signal coverage of large areas that are difficult to access for rebroadcasting in the usual way. To receive a satellite TV signal, special equipment is required. The standard set consists of a satellite dish, a bracket (mounting the antenna to a wall or roof), a converter, a cable and a satellite receiver (satellite receiver), the latter can be built into a TV or made in the form of a computer board. To watch satellite TV channels using the receiver, a TV or computer monitor is used (via a special built-in DVB-S card).
The transmission of information over long distances has been and remains one of the most important applications of artificial Earth satellites from a practical point of view. The first dedicated American communications satellite in 1963 had a transmitter of only 5 watts and an omnidirectional transmitting antenna. That is why on Earth it was possible to receive satellite signals only with a special antenna about thirty meters in size. In order to isolate a weak signal from a background of noise, a complex and expensive quantum amplifier cooled by liquid helium had to be installed at the input of a ground-based receiver. Space technology developed, and in the 1970s it became possible to launch communications satellites into the so-called geostationary orbit, when the satellite seemed to be suspended permanently above one point on the earth's surface. The transmitter power increased, and the onboard antennas were replaced with directional ones capable of forming a narrow beam of electromagnetic energy, "illuminating" a relatively small part of the earth's surface. That is, the radiation power was not scattered in all directions, but was directed mainly to the addressee. As a parameter that would characterize not only the transmitter, but also the antenna, the so-called equivalent radiated power was introduced - the product of the power of the onboard transmitter and the gain of the transmitting antenna (meaning the gain effect associated with the fact that energy is concentrated and radiated only in a certain direction). The value of the equivalent power reached hundreds and then thousands of watts. As a result, terrestrial antennas were reduced by a factor of two or three, and the amplifier no longer required cooling with liquid helium. And yet, one could only dream of directly receiving a signal on a home TV during this period - the cost of a receiving station was about a million Soviet rubles. The world's first distribution television system "Orbita" began operating in the USSR in 1967. Then similar systems appeared in the USA, Canada, Indonesia, India and other countries. In 1977, a group of European countries organized the Eutelsat consortium to exchange television programs on the Eurovision network. The basis of the network was three leading and one backup satellite "Eutelsat-1", which were also used to transmit commercial TV programs in the 11 GHz band. Several more programs in this range were broadcast via the satellites of the international system "Intelsat" and the commercial satellite "Astra". Today, many television viewers are acquiring their own receiving systems, allowing them to receive programs from distribution systems. In 1983, when the first transmissions via the Eutelsat-1 satellite began, this required a receiving antenna with a diameter of at least three meters and equipment costing $20000. It took years of work of scientists and engineers to make a reality a "dish" with a diameter of 60 centimeters, which can be installed on a balcony somewhere in Izhevsk or Omsk and receive dozens of programs from different countries directly from satellites. Let's try to trace how television programs come to the viewer in transit via satellite using the example of NTV-plus. This system of direct satellite broadcasting (SNV) has been operating in Russia and has been constantly developing since the mid-1990s. Since February 1999, the Bonum-1 satellite, specially prepared for digital transmission, began operating in this network. Modern equipment for digital compression and digital transmission makes it possible to transmit through one trunk (transponder) of a satellite instead of one analog program up to six digital television programs, and with statistical compression - up to 8-10 and even 10-12. But the cost of the satellite equipment and the receiving facility increases significantly. At the time when the first network of direct satellite broadcasting was being created, the price of a digital tuner on the world market exceeded one thousand US dollars, while the price of an analog tuner was twenty times less. This predetermined the choice of the analog method. However, by 1999, the cost of a digital tuner on the world market had fallen to about $200. This made it possible to completely switch to digital broadcasting. So, from November 1, 1999, NTV-Plus switched to digital broadcasting. The advantages of digital broadcasting are undeniable. First, it is a 6-10 times reduction in satellite costs (per program); improvement of the threshold properties of the receiver; enhancing the real picture and sound quality. Secondly, it is the provision of additional services to the consumer, such as playback of the program guide on the TV screen, convenient channel selection, the ability to enter a password and age restrictions for viewers, sound in several languages, data transfer, changing the software of receivers over the air, etc. . You can choose the type of reception: individual or collective. If we limit ourselves to collective reception, then we can reduce the power of the satellite, since the receiving antenna is larger. At the same time, part of the potential audience will be lost. After all, even in Europe, with the extensive development of cable networks, the number of individual satellite subscribers is almost fifty percent. What can we say about Russia, where there is practically no experience in the functioning of paid cable networks and contractual relations between the broadcaster and the owner of the cable network. Therefore, the choice in favor of individual reception becomes obvious, which, however, does not exclude collective reception. The massive nature of the satellite broadcast network and the need to transmit "opening" signals over the air forces complex closing systems to be used. This is a necessary protection against numerous "hackers". Now NTV-Plus uses the digital closing system of France Telecom (France). The facts of its "piracy" disclosure have not yet been discovered, and if this happens, countermeasures are provided. The choice of the main energy parameters of the NTV-Plus system was due to many years of experience in creating satellites in Russia and other countries, as well as to the mass receiving equipment available on the market, and the appropriate size of the antennas of the receiving installation. For the NTV-Plus system, they began to use a satellite with EIRP 50-48 dBW. With modern low-noise amplifiers and tuners with improved threshold properties, the signal can be received with antennas with a diameter of 45-60 centimeters. With a coverage area corresponding to the European part of Russia, the trunk power on the satellite is 80-100 watts. The choice of frequency band was essential in the creation of the system. At an international conference in Geneva in 1977, they adopted a plan for the distribution of frequency channels and satellite positions in geostationary orbit. A similar plan was adopted for the Western Hemisphere in 1983. Each country in the Eastern Hemisphere received at least five frequency channels with a width of 27 MHz. According to the plan, each satellite should serve one or more territories corresponding to the borders of one country. The Soviet Union received 70 frequency channels at five orbital positions. Other systems operating in the 12 GHz band can rightly be called "direct satellite television", since reception does not require permission from the transmitting party, and the price of a receiving installation today is no more than the price of a high-quality TV. Back in the Soviet Union, it was planned to create a satellite system in the 12 GHz band, in particular, satellites designed to simultaneously transmit four TV programs in one wide beam (the territories of Kazakhstan, Ukraine), two medium-sized beams (Belarus, Uzbekistan and other republics of Central Asia) and one narrow beam (Baltic, Transcaucasia). The power of the on-board transmitters was assumed to be such that antennas with a diameter of 1,1 meters were suitable for individual reception, and 1,5 meters for collective reception, where mutual interference has an effect. To place the Bonum-1 satellite, the State Commission on Radio Frequencies issued a permit for the use of one of the Russian positions in the START range. "The satellite is the most important element of the system," writes L. Kantor in the Radio magazine. years. Its design is unusual. It has the shape of a cylinder, on the entire surface of which the elements of the solar battery are located. The rotation of the entire outer "glass" helps to stabilize the position of the satellite's axis in space. The inner part of the satellite, on which the receiving and transmitting antenna is located, remains motionless (t i.e., as it were, rotates relative to the outer "glass" in the opposite direction). The satellite is controlled from a station located near Moscow. As experience shows, its operational parameters are maintained with high accuracy: the error of maintaining the position in orbit and pointing the antenna is significantly less than the specified value of ±0,1 degrees. To do this, correction sessions are regularly carried out using the installed four corrective engines and the necessary fuel reserve. The satellite antenna is pointed either by a beacon signal combined with telecontrol signals, or by the Earth's disk. The beam of the transmitting antenna has a special shape corresponding to the required coverage area. It is also possible to switch transmitters to the second irradiator, which makes it possible to form a zone to the east of the main one. The payload of the satellite is eight working trunks with a flexible reserve (from three transmitters), creating at least 50 dBW in the specified zone EIRP. All trunks work around the clock, including during periods when the satellite is in the shadow of the Earth and its equipment is powered by batteries." Author: Musskiy S.A.
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