Bandwith of television broadcasting.

[Freddy79]

Hi

I live in Sweden. Sweden are switching to Digital Televison. Right now they are sending both digital and analouge. And I have some question about this.

1) How large is the bandwith capacity when you transmit television?. Especially Over the air. Especially in sweden.

2) Is the bandwith just a function of how large frequencey spectrum you allocate.

3) How many tv channels is it possible to broadcast. Is this just a simple division: Number of channels = total bandwith capacity / bandwith-per-channel.

4) A few months ago I saw the former swedish cultural minister say that by going digital more frequencey space, would be freed up. Allowing other services such as wireless internet to use this frequencies. Is this true?

5) What is the most commonly bitrate used by digital television channels today. And what is the bitrate of and old standard television channel?

Lots of question. Hope you can make thinks clear for me

[dphirschler]

Going from memory here. But I think the analog channels accupy 6mhz. The cable companies tend to pack in 6 - 10 digital channels into a 6mz space, so they are significantly compressed. I've seen as many as 13 digital channels in one 6mhz space.


Darryl

[dphirschler]

Just found this. It's a good read and explains it a lot better.
http://electronics.howstuffworks.com/dtv1.htm


Darryl

[mats.hogberg]

I can answer 5 (as I have a DVB-T receiver): The video bitrate seems to be 5000 kbps-ish (5285 from SVT2) with 448 kbps AC3 audio. However, the mpg is reported as 15000 kbps, so most authoring apps complains, but can be authored and played as DVD anyway.

/Mats

[Abbadon]

4 could be true, when the analog spectrum is not used by the TV stations, the government could lease it (profit) and be used for other purposes.

[sorinicu]

The bandwith is used in a more complex way on digital TV.
As for digital TV in Europe is different from american aproach.
While in US the HiDef has a big importance, in Europe "cramming" more stations in the same channel is more important (same definition but more stations - more money by "renting" the same air space).
The big technical diference between US and Europe is that in US the broadcasters have their own antenas/emmiters and dedicated channels per station (like on analog TV) but in Europe there are just several "multiplexers" in a country and the broadcasters have dedicated "space" in that multiplex - space that is not a bandwidth but some kind of time division...

Read more about digital TV in Europe:
http://en.wikipedia.org/wiki/Digital_television_in_Europe
And more techical:
http://en.wikipedia.org/wiki/Digital_television#Bandwidth

[RabidDog]

I think here in the Uk its a similar situation. The idea is that in 2012 they will switch off the analogue signal completely. There are five stations per multiplex and i think about 30 digital stations in total(so six multiplexs?). The "old" analogue airwaves will then be rented out for a vast sum to whoever decides they need it most. Hi-def Tv takes about 4 times the bandwidth of a std -def Tv signal .. so i'm not sure how that fits into the digital picture.. even tho the beeb is trialling hi-def freeview (nature docs in hi-def.. its what it's designed for!)

[edDV]

...

4) A few months ago I saw the former swedish cultural minister say that by going digital more frequencey space, would be freed up. Allowing other services such as wireless internet to use this frequencies. Is this true?

I'm not up to date on plans in Sweden but I can comment on worldwide application of digital broadcasting.

In simple terms, analog broadcasting began in current form after WWII when 50-250MHz VHF was prime and UHF ~400-800MHz was considered experimental or short range.

Big TV mostly staked out the easier, longer distance VHF band. As wireless technology developed over the past 60 years, VHF TV stations became an obstacle because of the bandwidth they occupied and the interference they caused due to high power.

During the 90's in the USA, it was made a priority to push TV up frequency into UHF and change the technology so that TV stations could be placed closer together in spectrum so that massive amounts of RF spectrum would be freed from TV broadcasting and made availalble* to new wireless (telecom and computer) services. The result was ATSC digital broadcasting. It was determined that the two technologies would operate in parallel for a few years. Then (current plan is 2009), analog would be shut off.

In the USA preference was for individual 6MHz digital TV stations operating massive transmitters over long distances. Europe favors a larger number of short distance small transmitters each carrying multiple stations. This results from geography and political organization. DVB suits Euro needs.

Yes, this will free spectrum once analog broadcasting is tuned off.

5) What is the most commonly bitrate used by digital television channels today. And what is the bitrate of and old standard television channel?

Lots of question. Hope you can make thinks clear for me

Analog stations in Europe occupied 6-8MHz per broadcast channel. Bitrate doesn't apply to analog (PAL) broadcasting, but newer modulation technology offers ~ 25-50 Mb/s digital streams or more within a 7MHz analog spectrum. It keeps going up as technology improves.

Typical SD (720x576) single channel digital rates are 2-5 Mb/s
Typical HD (1280x720p, 1920x1080i) single channel digital rates are 14-25 Mb/s

In other words, up to 10 digital SD channels or 2 digital HD channels can be carried in the RF spectrum space of one analog channel.



* The USA plan is allocate some of the freed spectrum to government use (e.g. emergency communications) and to auction the rest to private industry as long term leases. The expectation is to draw substantial funds from industry that can be applied against the federal deficit.