[opendtv] Re: ATI equivalent to 5th gen LG?
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 13 Dec 2004 16:37:27 -0800
Bert wrote:
>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.
I certainly agree that multipath is the major DTV reception impediment,
particularly given that new "science" is required to resolve this very
tricky issue. Good RF design is a known and available quantity but I don't
believe that Zenith has released specifications for the tested 5th Gen
receiver. Therefore we likely can't make a judgement as to how much that
receiver's front end might also have contributed to it's success in
Baltimore and New York, which are tough RF areas. Does anyone know details
of the Zenith receiver's specs?
Clearly a DTV receiver requires improved RF front end performance, relative
to analog, to assure that the lowest possible TOV C/N is achieved when
operating in the soon to be "packed" RF environment. The standard Analog
version of today, which was designed for operation in the FCC managed UHF
spectrum or even worse, in the cable environment, is simply not sufficiently
robust.
----- Original Message -----
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
Sent: Thursday, December 09, 2004 1:50 PM
Subject: [opendtv] Re: ATI equivalent to 5th gen LG?
> 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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