[opendtv] Re: DVB-T HDTV demo using 19.7 Mbps in a 6 Mhz channel in costa rica
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 6 Mar 2006 12:00:45 -0500
John Shutt wrote:
>> "...the field this difference shrank to 2 dB. Sinclair
>> suggests that this may be due to the effect of real
>> world impairments that add to the theoretical 'gaussian'
>> channel values."
>
> What is the point of your quote? It reinforces what was
> actually observed in the field by over a hundred different
> observers over the course of a summer in 1999. You think
> you can tell the difference in 2 dB of sensitivity in your
> living room with your receiver?
You didn't pay attention to the last sentence, John. Let me paraphrase:
"The reason the theoretical C/N advantage was not witnessed in the field
was probably due to some level of multipath, which degrades 8-VSB
reception to less-than-gaussian levels of performance. In early
receivers, these impairments degraded the C/N margin in 8-VSB
significantly. With better demods, the expectation would be that the
theoretical C/N advantage in 8-VSB would be restored."
Watching the excellent signal monitor in the Accurian/Digital Stream
boxes, which includes an SNR display, I can say that a 3 dB difference
is not to be ignored. And also, that the 15 dB number is predictable and
achievable, not theoretical or rare.
And it's far better to read and understand reports rather than despair
based on faulty assumptions.
Bert
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