[opendtv] Re: Let the games begin
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 09 Nov 2006 20:47:44 -0500
Mark Schubin wrote:
I agree that the economic model for MovieBeam seems weak, and it
holds no attraction for me whatsoever, but Bert was questioning the
SNR requirements, and I haven't heard of a single complaint about that.
Complaint? You misunderstood my point.
The fact that Dotcast can put 4.5 Mb/s along with an analog signal on the
same carrier is easily explained. They need 40 dB of C/N to make this work.
And they won't sell you the system unless they determine, ahead of time,
that you will have adequate signal. So, high power, close range, and you
have to be cleared before you buy. Of course you'll hear no complaints.
If Moviebeam were available in Baltimore, would they offer it to me, 50
miles away as the crow flies? I doubt it. So you won't hear me complain
about reception. Does that prove Moviebeam is great stuff? No. It only
proves they won't give me the opportunity to complain.
Let's compare. You can transmit 4.5 Mb/s over normal 8-VSB with 15 dB of C/N
margin, and send along HDTV or a couple or three of SDTV channels to boot,
not just one NTSC. And you can do this at a range that is far, far from any
Grade A NTSC contour. E.g., especially with 5th gen receivers, 50 miles with
indoor antenna in a regular house, is not rare by any means. So I could in
principle get perfectly good Moviebeam service from Baltimore, to an indoor
antenna, if it were offered over 8-VSB. Plus HDTV. But no way with Dotcast.
Analog from Baltimore to my indoor antenna is extremely poor.
Or they could play it safe and only sell to local folk closer in to the
transmitters, with 5th gen receivers, and avoid complaints that way. And
still require *far* less than 40 dB of C/N.
This discussion was somehow associated with the A-VSB discussion. It's
apples and oranges, but since A-VSB and Dotcast at 4.5 Mb/s were mentioned
together, the difference in C/N margin is 40 dB for Dotcast vs 1.7 dB, or
4.5 dB, for A-VSB. That's a huge difference. Granted, that's without TV
programming on the A-VSB channel. So cut that down to 1.5 Mb/s of A-VSB, and
you can add a very nice few SD channels and get extremely robust Moviebeam.
Bert
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