[opendtv] Bolivia TV standard mystery

  • From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 19 Dec 2006 21:10:07 -0500

Is it NTSC-M or NTSC-N? I searched and found sites that claimed either one. The most interesting answer was "both."


claims NTSC-M for VHF, NTSC-N for UHF, in Bolivia. That would be very weird. Another site says "N(M?)," and 625 lines.


The more interesting question is, what DTT will they go to?

By the way, I was looking through the otherwise very good FCC report FCC/OET 99-2, which is that original 8-VSB vs COFDM comparison and includes the Sinclair test results and more.


But I choked on this paragraph, back in page 26:

"Mobile and Single Frequency Network Operation. COFDM has an advantage in its ability to support large single frequency network operation and mobile operation over large geographic areas. For example, this would allow use of a single channel to provide the same programming concurrently over a very wide area, perhaps an entire country, and in this way could better support mobile service. In this regard, such an approach would avoid the problem of leaving the service area of an individual station during a program while travelling. This is the approach that some European countries are pursuing. However, to implement this approach in the United States would necessitate a substantial change to structure of the broadcast industry and the way it is regulated."

That's insane. Maybe this is why so many people are laboring under such misconceptions regarding SFNs and COFDM.

In a nutshell, the advantage of COFDM over a single carrrier scheme, wrt SFNs, is that as long as the towers are *all within a round trip delay no longer than the GI*, all receivers in the area will be able to survive the multipath and the towers can be passive repeaters. But obviously, it would be ridiculous to design a large area SFN that way. You'll soon find places where the GI is way exceeded, and you'll have oodles of towers everywhere.

So if you want to create a large area SFN, suddenly you're faced with a very tricky problem which requires both synchronized towers and the use of directional antennas for many of the receiver sites. And guess what? Suddenly the COFDM advantage has essentially vanished. Reason being, with synchronized towers, even a single carrier scheme can be adjusted for mainly lagging echo, for loud echo, and even 2nd gen equalizers can do that rather well.

And no one does it that way, not even in Europe, in spite of what the FCC was being fed.

The report was good, though, and mostly on the mark. Too bad it took 4-5 generations before things got reasonably good for 8-VSB, rather than just 2 or 3 as they were saying. Too bad also that so many people continue to believe the marketing hype of those days.


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