[mythtv-users] HDTV, Myth, HD-2000, HD-3000, questions galore (and hopefully answers from the smart people... )

[Cory Papenfuss]

On Tue, 18 Jan 2005, Cook, Garry wrote:

> I've been watching this thread with interest, but have a question
> regarding statements referring to "over cable". Are we speaking about
> digital cable, or analog?
> Forgive me if QAM or some other acronym should easily answer my
> question. I'm not yet familiar with all of the terms.
>
 	There are a number of subtle issues going on here.  The basic 
thing is that a pcHDTV-[23]000 is essentially a one-way modem (I guess 
that's just the dem then... :).  All it does is receive an analog signal 
and decode its modulation.  The digital-to-analog modulation scheme for 
over-the-air HDTV in the US is 8-VSB, which the pcHDTV-[23]000 cards 
currently support.  The modulation scheme typically used for cable tv 
systems' "digital cable" is a different type, called QAM.  Since it's 
essentially just reprogramming how to interpret the 
downconvertered/sampled data, it's essentially a firmware upgrade 
(assuming computational power isn't an issue).  Thus, it's possible to 
receive "digital cable" with nothing more than the 1-way modem provided by 
the pcHDTV-[23]000.

 	That said, many/most digital cable system encrypt the signal.  So, 
while the QAM demodulator can receive the bitstream, it's encrypted and 
cannot be played without decrypting it.

Hope that helps,
-Cory

*************************************************************************
* Cory Papenfuss							*
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University 			*
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