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Digital Video Broadcasting (DVB)

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    Posted: 14/August/2008 at 16:19

Digital Video Broadcasting

Let's take a look at one of the most common uses for satellites.

Digital Video Broadcasting (DVB) is the method used for all digital TV and Radio broadcasting which is now a multi-million pound industry. To recieve DVB from Satellite (DVB-S) is not as expensive as it is to transmit it. All that you would need is a suitable steerable motorised satellite antenna and motor controller, a suitable Feed with LNB and a PC with a satellite receiver card. Alternatively, you could buy a Satellite TV dish and receiver, this is also a DVB-S receiver.

So why buy anything else? Well, having spent a few hundred pounds on a PC setup with a motorised dish, you could tune in and point at more than just one satellite. This opens up a variety of normally unseen channels for your viewing pleasure. For example, the news feeds from war torn countries are to be found on a variety of satellites that bring the news reports back to this country or europe generally. From there they are sent to the news studio where they are edited into the program. Then the news program is sent via satellite for us to see at home.

But whats the point? It's quite ammusing to watch those galant war reporters rehearsing their lines, messing with their hair and generally standing about for long periods of time. Sometimes the engineers that put the uplinks together and test the feeds are to be seen having fun and cracking jokes in front of the camera. Not all of these uplinks are available as some are coded.

 

How does it all work?

Well the satellites all sit on a geostationary arc around the equator. Whether you are north or south of the arc is irrelevant. The satellites almost cover the whole planet in this way, so when a european news reporter in South Africa wants to send his live report back to the news room, he gets booked onto a satellite that can be seen from South Africa aswell as Europe. The time on the satellite is charged and is not cheap so the news room has to try and fit in the report with the rest of the news and then the report is made.

If the news room run out of time then the satellite time is wasted. Often the time is shared amongst a group of reporters from different news channels so that if the report is cancelled the overall cost is reduced because another reporter can step in. Having said that we have seen many feeds of countryside and mountains with nobody in site for over half an hour. This is probably the engineering setup time, or a handover between reporters. There is no point shutting down a link only to bring it back again in half an hour.

How do the reporters uplink their story?

Aha, yes indeed, this is a good question. There are a number of companies making a number of 'Fly Away' satcom terminals which are specifically designed for satellite news gathering (SNG). These terminals are fairly small, self contained uplink terminals that have video and audio inputs and outputs, digital MPEG-2, 3 or 4 video & audio encoders, engineering audio channels, upconverters, amplifiers and an antenna. They probably have receivers aswell but not always.

There are even companies selling all of this technology in a brief case. Quite simply you can now get on a plane with a small handheld digital video camera and a briefcase uplink system, fly to a war zone and report back in minutes of your arrival. The lower the data rate of the uplink the lower the quality of the video. For rapid links I have seen many a report which is more sound than video and is actually similar in quality to the early mobile phone videos.

So what are you waiting for? Go out and buy a 1.2m satellite antenna, a receiver card for your PC and start receiving those news feeds. Maybe not, but for those of you who are mad on satellites and want to know whats out there, they are free to air (FTA). No subscription required, all you need to know is on which satellite to find them, at what frequency and a few other parameters. You can get all this information at : SATCODX http://www.satbeams.com/ and also at http://www.lyngsat.com/ both of these sites provide detailed information on the satellites and channels so you can find out where to look.

If you want to get the movies and other pay to view channels you will need a Conditional Access Module (CAM) which is sometimes part of the decoder card in the PC. These CAM's allow you to plug in your viewing card or freeview card which you can get from the service provider.

The SATCODX website (link above) provides information for every Digital TV and Radio satellite, this information includes the location of the satellite as well as the programme parameters for each transponder and channel.

Next we look at the end to end systems that use satellite communications.
 


Edited by Satcoms UK - 29/March/2015 at 19:20
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