Digital Cable TV vs Digital Terrestrial TV

[Lost.Cable]

Can anyone tell me the difference bettwen Digital Cable Televison and Digital Terrestrial Television?

If i have an Digital Terrestrial Receiveir, later on can i change to Digital Cable and still mantain my receiver or must i change it?

I Know that if i had a satellie receiver i coulnd't use it on cable, because of the frequencies. Right?!?!?!

 

[Topper]

Can anyone tell me the difference bettwen Digital Cable Televison and Digital Terrestrial Television?

Cable is received via a cable from a distribution node in the street which is supplied from a distribution amplifier which is fed by fibre optic cable. Beyond that I will not go as we do not discuss cable here this is a satellite forum
Digital Terrestrial is transmitted in much the same way as analogue indeed I think they are broadcast simultaneously through the atmosphere to an aeriel which then converts the signal into a small signal in a cable which feeds the receiver.

If i have an Digital Terrestrial Receiveir, later on can i change to Digital Cable and still mantain my receiver or must i change it?

You must change it

I Know that if i had a satellie receiver i coulnd't use it on cable, because of the frequencies. Right?!?!?!

Right..... amongst other things

 

[spiney]

Well, all digital tv is compressed via mpeg (version 2 only up till now, with newer version 4 for HDTV).

Also, both cable and terrestrial versions are delivered via QAM modulation schemes.

However, terrestrial also uses COFDM modulation (on top of QAM), so these 2 methods are NOT compatible! Even though the 2 different type boxes may have many similar bits inside, in the end these few differences still make them incompatible.

(This is because the conditions for signal delivery over coaxial cable are much better than for terrestrial broadcasting, which therefore requires extra "layers" in order to work at all!).

And, no, you can't use a satellite receiver on a cable delivery system, because satellite digital delivery uses QPSK, yet another different modulation scheme!

 

[RedDevil_UK]

If i have an Digital Terrestrial Receiveir, later on can i change to Digital Cable and still mantain my receiver or must i change it?

Yes you will...

@ Spiney
that sound like an explanation of a universal translator on the starship enterprise!! you would need 5 years at star fleet academy to know what that meant

basically what spiney is saying.... each company uses different methods of transmitting their services

so a different box is needed for each

 

[spiney]

Hmmmm .......

There's;

1) The bit common to all digital tv, MPEG2 (de) coding.

2) The bit that's different for each delivery system (modulation method).

That's because conditions are different in each case! For example, satellite needs wide bandwidth to cope with low power transmission, whereas the problem with terrestrial is mutlipath propogation (hence COFDM), and cable delivers at much higher power with low noise (in which respect, it's more like DVD than broadcasting!).

Some manufacturers have tried to "re-use" the MPEG bit for different systems, eg Fortec's Diamond sat/terr receivers, but that's a bit like taking the petrol engine out of your bike in order to use the lawnmower (!), really it's not worth bothering, a different box each time is much more convenient.