[Gllug] [Kind of OT] Digital TV

[Doug Winter]

On Thu 20 Mar Ashley Evans wrote:
> > Does the digital TV use the standard aerial?
> 
> There are two common types. "SKY" and "terrestrial". The former is
> MPEG-2 encoded video via a satelite dish. The latter is received
> through a regular a TV antenna, I'm not sure if it also uses MPEG-2 or
> not.

Yep, they all use MPEG.  They use different mechanisms for the
interactive elements though - Digital Terrestrial Television (DTT) uses
MHEG, Sky (DSat) use OpenTV and Cable (DCable) use DHTML.

DTT will work with a standard aerial in theory, but reception can be
unwatchable if you are in the wrong place.  Where analogue degrades at
least approximately gracefully (and your eyes very quickly stop seeing
analogue interference), digital signals degrade appallingly.   The
marketing about great reception before DTT launched was just a barefaced
lie.

On highly irregular surfaces (like the grass on football pitches) the
compression engine has real trouble, and any interference can cause the
picture to go very blocky.  Live broadcasts are poorer quality because
the compression engine has to compress on-the-fly, which means it
doesn't work as well.

Sky have significantly more available bandwidth than any DTT
broadcaster, and so are able to carry many more channels.  Cable can do
too (We've got 165 channels on cable at last count, and we get a few
more each week).  DTT is limited by the bandwidth allocated by
government - which will never be as many as sky or cable can supply.
Each channel takes between 3 and 6 Mbps.

DSat can be badly affected by adverse weather, as can DTT.  Cable often
take their signal for primary channels from sky or over satellite relay
from their own ground stations, so poor weather conditions can sometimes
affect that too - however their receiving equipment is obviously much
better than the tiny dishes you have at home.

doug.

-- 
http://www.britishsteal.com                        doug at pigeonhold.com
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"The United States is like the guy at the party who gives 
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