What is DTH ?

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DTH, a blooming trend in the present world of infotainment is actually an acronym of Direct To Home. Nowadays its most highly appreciated technology in all around the globe for high quality video transmission. As we have generally seen, it not only can transmit TV and radio, but it is also used for data transfer in several parts of the world. Since it makes use of wireless technology, TV channels are sent to the subscriber's television direct from the satellite eliminating the need for cables and any cable infrastructure. Then how does a DTH works then?? How can we get such high quality pictures via DTH than normal cable distributed TV channels??

Now let me quench the thirst of your curious mind one by one. First lets start with what is DTH ? DTH is generally a satellite television broadcast system. It is a kind of DBS-TV(Direct Broadcast Satellite Television). The TV signal you receive is directly received from the satellite. No intermediate connection is necessary. These TV broadcast are served by geostationary satellite (which is located at 36,785 km above earth surface). Looking at the history it is found that, first direct broadcast of video via satellite was done in the Tokyo Olympic games in 1968. Since then this technology is extensively used commercially in the field of satellite communications. This technology is the greatest source of revenue generation for satellite companies till date.

Although the digital video transmission was used since 1960s, it was not commercially applied. The receiver antenna was large  and the decoding of the signal was also a tedious task. But in 1990s, digital video transmission became feasible. The development of low cost and small sized antennas and receivers, high speed digital integrated circuits, error control mechanisms, encryption and decryption of MPEG format video made the DBS-TV practically realizable. This gave rise to the fully digital DBS-TV which is also known as Direct TV. This Direct TV is commonly called DTH.

Then Hughes Electronics Corporation started commercial use of Direct TV by launching its first satellite for DBS-TV in 1993. The satellite was called DBS-1. After the launch of DBS-1 the company started providing limited service to the civilians. In 1993 and 1994, DBS-2 and DBS-3 was launched. Since then several satellites are launched for DBS-TV transmission. Direct TV was the first brand in the field of DTH and it alone has more than 80 million customers till date. Other giant vendors for DTH transmission are STAR TV, Telestar, Echostar, DISH TV, Astro etc. For more details of DTH vendors click here. These companies provide use of their satellite for the transmission in other small countries.

We all know we have mainly two parts in a general DTH system. An outdoor part i.e. Antenna and another is indoor part i.e Signal decoder also known as “Set top box”. The antenna acts as the signal receiver. In antenna there is a combination of two types of antenna, one is parabolic reflector antenna (the curved shaped metallic plate) and another is feed (generally HORN antenna is used). Feed is kept in front of the parabolic reflector antenna facing towards it. It is the feed, which is directly supplied by the  signal. The parabolic reflector is used just for directivity of signal. In DTH telecast the signals are transmitted in Ku band(10.7 GHz to 18 Ghz) and are received by the subscribers through a small dish antenna (nearly 60 cm diameter) and a set top box. The simplified block diagram of DTH receiving system is shown below.

There is a block in the receiver which verifies the user identity/ account and checks for his balance then only will decode the received signal. In this way the cost control is done.

In addition to TV and radio transmission, some of the companies also provide data facilities. These data are also encoded as encoding of other video and audio signal and is transmitted. The receiving side extracts data from the received signal.

                        Figure: Detailed diagram of DTH transmission

Advantages:

·         Easy installation

·         User friendly

·         Portable and efficient for home user

·         High definition video transmission

·         Reliable

·         Economical

Disadvantages:

·         time delay (normally it has time delay of about 2 seconds, as it is the time required for signal to reach satellite and come back to earth again)

·         disturbed by bad weather.

·         Only one user can be served by one receiver

This was all I could help you understand. Its just introductory article so for more technical details you may contact me or use the references. Thanks for reading.

References:

·         Pratt,T., Bostian,C.W., Allnutt,J.E. “Satellite Communications”.2nd Edition.John Wiley and Sons.

·         http://en.wikipedia.org/wiki/Direct_To_Home

·         http://www.dishhome.com.np/what-is-dth