Currently, we are faced with the transition to digital broadcasting. But what does it actually mean? Digital technology is already in the production of radio and television twenty years ago. Now is the time for its implementation at the transmitter, one of the last links in the direction of listeners and viewers who depend on terrestrial reception.Digital television is a broad term. We must distinguish between the digital output (production program) and the actual broadcast - to send signals to our rooftop antennas.You can make the TV with the latest digital technology, and send it to analog or to produce in old-fashioned analog and transfer it to digital. So be careful when you talk about digital television.
If you do not know what the difference between analog and digital signals, take a look at this simple example. You can tell the size of a TV screen in two different ways. If you show the size of your hands, it is an analog value. The screen size is represented with the distance between the left and right hands. This distance can be arbitrarily small and the value (in this case, the distance between the hands or the size of the screen) can be any value from zero (both hands), and the maximum duration of your hands.
To report the screen size in the digital you would measure it with a meter tape or ruler, noting the number at the end of the screen and rounding that number to some appropriate number of decimal places. That number now is digital (numeric) screen size. What you did in fact analog-digital conversion. Now you have a number representing the size of the screen. Since you have a round number is not the exact value of screen size, but the value that is sufficient for most purposes. To measure the exact value will require an infinite number of decimal places that it is impossible to achieve, and we usually do not require that the exact number.
Why are we switching to digital television broadcasting? The main reason is the more efficient use of radio spectrum. In the analog world for each channel (program) took a single frequency (RF channels). The capacity of this channel is 6 MHz (USA) and 8 MHz (Europe). Number of radio spectrum available for television broadcasting is limited.Therefore, there are a number of channels (frequencies) that can be used for television broadcasting. We can reuse these frequencies, if we can ensure that the transmitters send at the same frequency are far enough away to avoid interference. Many countries have used all the frequencies assigned to them and further enhance the television stations with terrestrial broadcasting can not. New technology must be developed. And it was. Audio and video signals are digital and can be effectively compressed with different compression methods. Digital broadcasting can use one frequency channel to transmit packets of compressed television, radio and data services is called a multiplex.
Different digital standards were developed. ATSC is used in North America, DMB-T is used in China, ISDB-T is used in Japan, while Europe, Australia and many other countries have decided to use DVB-T. Each of these standards transmits digital data stream. This transport stream contains compressed audio and video. There are two popular codecs or compression algorithms (standards) used for compression: MPEG-2 and the new, higher level MPEG-4. All of these standards are incompatible, and you need a digital receiver (Set-Top-Box), which is compatible with the transmission and compression standards used in your country.
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