[mythtv-users] HDTV, Myth, HD-2000, HD-3000, questions galore
(and hopefully answers from the smart people... )
Cory Papenfuss
papenfuss at juneau.me.vt.edu
Tue Jan 18 11:52:55 EST 2005
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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