A digital satellite receiver is an indoor box-shaped appliance that takes in the signal captured by a satellite dish and feeds it to the connected television set. It is the last important piece of equipment that completes the process by which a satellite TV broadcast is received and watched by a viewer. There are other kinds of digital receivers, such as those used for cable TV. All of them are commonly called set top boxes; derived from the customary shape and because such devices are also usually set on top of a television. The differences between a digital satellite receiver and other set top boxes is that it is specifically designed to accept satellite TV signal frequencies (from 950 to 2150 megahertz) and unscramble the particular manner in which such signals are modulated for transmission.
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Just like cable TV, satellite TV can only be availed through paid subscription. Since TV signals transmitted via satellite are indiscriminately broadcast on a large area, these signals need to be encrypted so that only subscribers are able to view the shows and programs on the hundreds of channels that are offered by a satellite TV service. Inside each digital satellite receiver is a chip that can unlock and decode the signal. The security measure that this chip performs is unique for each satellite TV service provider. Thus non-subscribers who may have their own satellite dishes and digital receivers are unable to watch the shows on their television sets, even though they may physically pick up the signal.
A TV signal contains a huge amount of information. It would take enormous power and a very wide frequency range to transmit and broadcast video and audio data as it is viewed and heard by human audiences. Therefore, compression is necessary to make the whole process efficient. Digital satellite TV signals are commonly condensed into MPEG-2 or MPEG-4 format. These are the same compression formats used to effectively transfer or stream multimedia content on the World Wide Web. A digital satellite receiver takes this compressed digital TV signal and converts it into an analogue format that a typical television set can output. With newer television sets that are designed to take in digital signals, conversion is no longer necessary.
TV signals are radio waves and radio waves are modulated in order to be able to carry information. Older and more common ways of modulating radio waves are amplitude modulation (AM) and frequency modulation (FM), and these are the two ways of tuning in on radio. For satellite television the modulation standard is known as Digital Video Broadcasting or DVB-S. The "S" stands for "satellite" and distinguishes this method from the modulation standard used by cable television, which is denoted as DVB-C. Satellite TV service providers use a technique called multiplexing to mix and cram together several channels into a single transmission. When this single transmission reaches the subscriber, the digital satellite receiver extracts individual channels and feeds it to the television set.
Aside from the basic function of processing a satellite TV signal, digital satellite receivers may have other features built into them by their manufacturers. One popular feature is the capacity to record digital video. Recording television shows is possible through an internal hard disk much like that of a personal computer. The show is written and stored in the digital satellite receiver's hard disk and can then be viewed at a later time.
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