Direct to Home is a term used to refer to satellite television broadcasts intended for home reception, also referred to more broadly as Direct broadcast satellite (DBS) signals. The expression direct-to-home or DTH was, initially, meant to distinguish the transmissions directly intended for home viewers from cable television distribution services that sometimes carried on the same satellite. Direct broadcast satellite, (DBS) also known as "Direct-To-Home" is a relatively recent development in the world of television distribution. “Direct broadcast satellite” can either refer to the communications satellites themselves that deliver DBS service or the actual television service. DBS systems are commonly referred to as "mini-dish" systems. DBS uses the upper portion of the Ku band, as well as portions of the Ka band. Modified DBS systems can also run on C-band satellites and have been used by some networks in the past to get around legislation by some countries against reception of Ku-band transmissions.
Technical aspect of DTH
There are five major components involved in a direct to home (DTH) satellite system: the programming source, the broadcast centre, the satellite, the satellite dish and the receiver.
Programming Source
Programming sources are simply the channels that provide programming for broadcast. The provider (the DTH platform) doesn’t create original programming itself; it pays other companies (HBO, for example, or ESPN or STAR TV or Sahara etc.) for the right to broadcast their content via satellite. In this way, the provider is kind of a broker between the viewer and the actual programming sources. The broadcast centre is the central hub of the system. At the broadcast centre or the Playout & Uplink location, the television provider receives signals from various programming sources, compresses using digital compression, if necessary scrambles it and beams a broadcast signal to the satellite being used by it. The satellites receive the signals from the broadcast station and rebroadcast them to the ground. The viewer’s dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer’s house. The receiver processes the signal and passes it on to a standard television. Lets look at each step in the process in greater detail. Satellite TV providers get programming from two major sources: International turnaround channels (such as HBO, ESPN and CNN, STAR TV, SET, B4U etc) and various local channels (SaB TV, Sahara TV, Doordarshan, etc).
THE BROADCAST CENTER
The broadcast centre converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of data — about 270 Megabits per second (Mbps) for each channel. In order to transmit the signal from there, the broadcast centre has to compress it. Otherwise, it would be too big for the satellite to handle. The providers use the MPEG-2 compressed video format. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to about 3 or 10 Mbps (depending on the type of programming). This is the crucial step that has made DTH service a success. With digital compression, a typical satellite can transmit about 200 channels. Without digital compression, it can transmit about 30 channels. At the broadcast centre, the high-quality digital stream of video goes through an MPEG-2 encoder, which converts the programming to MPEG-2 video of the correct size and format for the satellite receiver in your house.
ENCRYPTION & TRANSMISION
After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable data) if the receiver has the correct decoding satellite receiver with decryption algorithm and security keys. Once the signal is compressed and encrypted, the broadcast centre beams it directly to one of its satellites. The satellite picks up the signal, amplifies it and beams it back to Earth, where viewers can pick it up.
THE DISH
A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam. The dish on the receiving end can’t transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point. In this case, the point is the dish’s feed horn, which passes the signal onto the receiving equipment. In an ideal setup, there aren’t any major obstacles between the satellite and the dish, so the dish receives a clear signal. In some systems, the dish needs to pick up signals from two or more satellites at the same time. The satellites may be close enough together that a regular dish with a single horn can pick up signals from both. This compromises quality somewhat, because the dish isn’t aimed directly at one or more of the satellites.
THE RECEIVER
The end component in the entire satellite TV system is the receiver. The receiver has four essential jobs: It de-scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that programming package. The provider can communicate with the chip, via the satellite signal, to make necessary adjustments to its decoding programs. The provider may occasionally send signals that disrupt illegal de-scramblers, as an electronic counter measure (ECM) against illegal users.
It takes the digital MPEG-2 signal and converts it into an analog format that a standard television can recognize. Since the receiver spits out only one channel at a time, you can’t tape one program and watch another. You also can’t watch two different programs on two TVs hooked up to the same receiver. In order to do these things, which are standard on conventional cable, you need to buy an additional receiver. Some receivers have a number of other features as well. They pick up a programming schedule signal from the provider and present this information in an onscreen programming guide.
BY - KUMAR KAMAL
Good One Kamal..Informative, Crisp and very simple and educative read..hope to see more coming from you..!
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