[opendtv] Re: DVB-T HDTV demo using 19.7 Mbps in a 6 Mhz channel in costa rica
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 06 Mar 2006 20:36:04 -0500
I usually figure that, on the scale of:
actual -> real -> virtual -> fantasy -> modulation debates
there is at least a 10 dB step on each.
- Tom
Mark Aitken wrote:
> In some stable condition locations, where the variation is small, 2dB
> can make a difference. If there does indeed exist a 20-25dB variation
> from some particular location, I can scantly think that 2dB makes THAT
> big of a difference...
> Is there a difference in the real world versus an actual real world?
>
> Doug McDonald wrote:
>
>
>>John Shutt wrote:
>>
>>
>>
>>>Doug,
>>>
>>>Thank you for confirming that atmospherics will cause more than a 2 dB
>>>difference in the received signal.
>>>
>>>John
>>>
>>>
>>
>>
>>More than 2 dB?? Of course more than 2 dB ... it's more like
>>20 or 25 dB!!!
>>
>>HOWEVER ... its seasonal. In stable seasons it can sit
>>stably for weeks. Only in late summer or fall do you see
>>frequent sharp upward spikes of up to 25 dB. Only in early
>>winter do you see the small but significant downward dips.
>>
>>And as I said, a 2 dB difference in signal power from the
>>transmitter makes a DRAMATIC difference in the useability of
>>a station in the presence of these fluctuations.
>>
>>The fact that there are fluctuations due to tropo conditions
>>is a reason why a 2 dB difference DOES matter, not why it
>>does NOT matter. THAT'S MY POINT, in the real actual world.
>>
>>Doug McDonald
>>
>>
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