[opendtv] Re: Mobile TV: $2 Billion in Ad Buys

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 21 Apr 2008 14:05:57 -0400

John Shutt wrote:

> One DVB paper I have claims a 3 dB difference between HM and
> non-HM 64QAM, 3/4 FEC 1/16 GI in an 8 MHz channel.
>
> Another DVB paper of the same vintage claims 19.6 dB Gaussian
> for the LP stream in a 6 MHz channel for the NAB 2000 HM-COFDM
> demo.
>
> The link was to show that in the real world, 3 dB is not a
> meaningful difference in reception in the far field.

But I have seen the C/N margins at work with the Accurian's signal
monitor, and a 3 dB difference is indeed huge. The difference in
reception quality between a station squeaking in at around 15.x dB of
C/N, ane one coming in just slightly higher than that, like 16 dB, is
very pronounced.

The monitor does bounce around, but only by fractions of a dB, when a
station comes in solid. Which means, there are stations out there, like
for example WMPT-DT, that are always under 19 dB of C/N, and yet I can
receive them reliably. So for me, it does matter.

As I showed you on numerous occasiuons, Sinclair showed a real-world
difference of only 2 dB in reception in the far field, *and* speculated
that possibly this was due to the other flaws in the design of those 1st
gen receivers.

> And again, for about the one thousanth time, it is a tradeoff,
> but one that each individual broadcaster can make to best fit
> their own business model, not one tradeoff made by an
> engineering committee and thrust upon the world.

And for the 1001st time, no one ever disputed the advantages of
adjustability. But it would be nice to have that without paying a price
that the FCC planning factors wouldn't accommodate, right?

Bert
 
 
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