Direct to Home (DTH) technology

Direct-to-Home satellite broadcasting or DTH is the distribution of television signals from high-powered geostationary satellites to small dish antennas and satellite receivers in homes across the country.

Early satellite television was broadcast in C band - radio in the 3.4-gigahertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (10 GHz to 14 GHz).

The Components

There are five major components involved in a direct to home (DTH) or direct broadcasting (DBS) satellite system: the programming source, the broadcast center, the satellite, the satellite dish and the receiver.

a) The programming source
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 (SaBe TV, Sahara TV, Doordarshan, etc). Turnaround channels usually have a distribution center that beams their programming to a geostationary satellite. The broadcast center uses large satellite dishes to pick up these analog and digital signals from several sources.

b) The broadcast center 
The broadcast center 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 center has to compress it. Otherwise, it would be too big for the satellite to handle. The providers use the MPEG-2 compressed video format — the same format used to store movies on DVDs. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to about 3 or 10 Mbps (depending on the type of programming).

With digital compression, a typical satellite can transmit about 200 channels. Without digital compression, it can transmit about 30 channels.

c) Encryption & Transmission 
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 center 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.

d) 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.

The curved dish focuses incoming radio waves onto the feed horn.

e) 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. It takes the digital MPEG-2 signal and converts it into an analog format that a standard television can recognize.

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. Many receivers have parental lock-out options, and some have built-in Digital Video Recorders (DVRs), which let to pause live television or record it on a hard drive.

Advantages of DTH Technology
► The main advantage is that this technology is equally beneficial to everyone. As the process is wireless, this system can be used in all remote or urban areas.► High quality audio and video which are cost effective due to absence of mediators.► Almost 4000 channels can be viewed along with 2000 radio channels. Thus the world’s entire information including news and entertainment is available to subscriber at home.► As there are no mediators, a complaint can be directly expressed to the provider.► With a single DTH service consumer will be able to use digital quality audio, video and also high speed broadband.► It also offers interactive channels and program guides with customers having the choice to block out programming which they consider undesirable.