Information technologies and, in particular, free satellite tv also have strongly taken for a long time the major place in our daily life. The satisfaction of an increasing demand of the population on qualitative (in technical sense) TV is, undoubtedly, complex problem. Along with rapid development of satellite television projects, building of powerful transferring television centres, relaying lines of transfers, deployment of systems MMDS, building of systems free satellite tv occupies, rather extensive, a niche in the decision of the specified problem. First, creation free tv is economically attractive on today's, is far not idle time, the moment owing to possibility of attraction of off-budget investments. Secondly, satellite tv with success can solve a problem of maintenance of huge number of subscribers a qualitative television signal in the conditions of dense city building where conditions of reception from an aether are far ambiguous, and with use of fibre-optical technologies there is possible an association enough the remote and various areas on population density in large uniform user networks that is very important for the Russian open spaces. Besides, become far not each consumer of television services can now the user of systems of a direct satellite announcement.
As the number telebroadcasting free satellite tv channels, both radio, and satellite, constantly increases, not far off an era digital free TV, with its huge information potential, quality sat systems becomes one of the major parametres. The working range of frequencies of 47-230 MHz became obviously insufficient. Its expansion at least to 860 MHz is necessary. Besides, it is already not enough to have only an information stream "downwards", i.e. towards the subscriber. For diagnosing of a condition of system free satellite tv and monitoring presence of an "ascending" information stream towards the head equipment is necessary. Besides, by granting to subscribers of additional services.Thus, the question on designing and building of broadband, interactive cable networks is actual for today.
Construction principles satellite tv
The analysis of principles of construction of modern systems free satellite tv shows, that one of mainstreams of their development are association and integration of isolated small networks with simultaneous increase in number broadcast free satellite channels and granting to subscribers of other information services (except broadcasting of TV-programs). It can be connection to a telephone system, transfer systems viewsat files, access to Internet, gathering of the information from a different sort of gauges and a number of other services. All it as it was spoken above, conducts to expansion of a spectrum of the frequencies occupied in a network with transferred signals. And necessity of maintenance of high quality of a signal at the subscriber makes corresponding demands to the head, main and user's equipment.
If at the decision of the above-named problems to be guided by the traditional environment for signaling free satellite tv from head station to subscribers - a coaxial cable to realise in practice all these requirements it is possible only under condition of an expense of very considerable means.
The matter is that expansion of a strip of broadcast frequencies (number increase fta satellite channels) demands application of the main amplifiers with the raised resulted dynamic range (that is smaller factor of strengthening at the set level target satellite a signal). And decrease in factor of strengthening of in cascade included amplifiers causes increase in their number that results not only in decrease in the final relation a signal/noise, but also to reduction of the relation a signal / a combinational hindrance at the expense of accumulation of "collateral" frequency products on a highway. Owing to it the maximum number of consistently included main amplifiers cannot exceed certain quantity (usually no more than 7-10) which depends on a dynamic range and noise characteristics of concrete type of amplifiers. Accordingly, it imposes restrictions and on possible length of a highway. And it, in turn, leads to necessity to increase quantity of head stations satellite tv, subscribers serving certain number. If to consider, that cost of one channel of head station of the second class makes a $0,5-1,0 thousand order, it becomes clear, that the increase in number of channels except purely technical problems causes also financial difficulties.
These problems can be solved, having replaced the main coaxial cable on the fiber-optical. On this way the majority of the countries of Europe, the USA and Japan has gone. We will list short main principles of construction of modern networks free satellite tv
Isolated networks satellite TV are integrated, forming the integrated systems of a cable television;
As system basis free satellite TV the head station (for example manufactures of firms Barco, IKUSI, Blancom, WISI, TERRA), providing translation in a cable network as TV-signals of all kinds (satellite, radio, digital), and radio programs (including stereophonic) serves;
The basic transport highways of system in direct and return directions are fiber-optical communication lines of high throughput which provide signalling of all kinds from head station to places of residing or work of subscribers of system satellite fta tv;
To subscribers of system various services of interactive service (a telephony, telex communication, access possibility to Internet and other kinds of communication) are rendered, that is provided with a corresponding choice of the head and main equipment satellite tv networks (first of all quality and presence of the return channel) and necessary user's terminals;
Fast development of technologies free satellite tv (first of all what are connected with perspective digital methods of modulation, time and frequency consolidation of signals) opens the broadest possibilities for transfer of various types of information with use of the flexible hybrid information environment. The modern cable network should provide transfer viewsat files with a speed some honeycombs of Mbit.
The basic services of interactive service at an initial stage are the telephony and access in Internet;
The head station should incorporate the built in equipment of the control and system monitoring;
Let's underline especially a principle of modular designing of large networks free tv. At construction of the big systems which can be created by simultaneously different groups of developers and when it is necessary to provide functional compatibility of various parts, flexibility and possibility of improvement of parametres without radical reconstruction and functioning infringement, it is expedient to use methods of blochno-modular designing free satellite tv.
