[opendtv] Re: ATI equivalent to 5th gen LG?
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 9 Dec 2004 16:50:52 -0500
John Shutt wrote:
> The problem with the ATSC guidelines is that it is
> very difficult to put into words the reception
> behavior of the Zenith 5th gen chips.
Are you sure, John?
This might have been true back in the late '90s, but
I think that the measures of effectiveness are
getting to be much better understood now. Whether
or not the ATSC guidelines cover these quantitatively
enough now is another matter.
What makes the 4th gen Linx and 5th gen LG receivers
obviously different is not that mysterious:
1. Symmetric echo tolerance out to +/- 40 usec (rather
than only 40 usec lagging).
2. C/N margins around 20 dB for reception in severe
multipath, for both tracking and symbol sync.
3. Capable of solid reception in Brazil E profiles
(i.e. in the presence of three 0 dB echoes spaced
about 1 usec apart).
I think that these 3 attibutes are the most important
differences between the inadequate receivers that came
before the Linx or LG, and receivers that work. The
other parameters, e.g. adjacent channel selectivity,
sensitivity, dynamic range, dynamic echo tolerance,
are not substantially better than older receivers, and
could most likely stand improvement still. But
evidently, these other factors were not the weakest
links.
The way I see it, if COFDM receivers worked but
ATSC receivers did not, what were the differences?
Well, the above 3 points were obvious differences. In
fact, even COFDM receivers had a tough time in Brazil E.
I don't think there's any huge mystery here.
Matter of fact, item #2 alone, which first was met by
a Samsung receiver back in 2002 IIRC, immediately showed
promise in Mark Schubin's apartment by being the first
to achieve solid reception of any channel at that site.
Compare this with COFDM and see why.
Bert
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