John Willkie wrote: > Rember, in this context, that 8-VSB is supposed to be the equivalent of NTSC, not the better of it. Yes, I guess that is true but it's such a bad decision I wish we wouldn't perpetuate it. > Upshot: for all it's superiority, permitting COFDM would have provided a superior signal level to that of NTSC, and -- aside from narrow technical modulation issues -- would have unwound the carelfully (politically) negotiated replacement of NTSC with an equivalent service level from 8-VSB. To permit COFDM, broadcasters would have had to pay a heavy price (or prices). Sorry, you completely lost me on that one. What heavy price are you talking about? - Tom > Several weeks back, mono-note Dermot, while continuing his consistent praise > of OFDM modulation over VSB, spilled the beans on why OFDM was inappropriate > as a replacement for NTSC in the U.S. > I don't know if my friend Dermot fully realized the upshot of his comments, > and I suspect that only a few list members caught the import of his comments. > It took me a week or two of pondering to realize the implications. > > What the heck am I talking about? Well, we were discussing probablity eg, > f(50,50) of reception with various schemes. Rember, in this context, that > 8-VSB is supposed to be the equivalent of NTSC, not the better of it. > > Dermot bragged how goold fashioned COFDM routinely offered F(50,90) reception > probability over entire coverage areas, and with -H, it was F(50,99) (or was > it F(99,99)? > > These figures sound great. For the uninitiated, that means that at fifty > percent of the reception locations, at least 90% of the time, a sufficient > signal level was received. (Analog also imposes a grade of service figure > before these reception levels are relevant, but I'll table that here.) > > Unfortunately, as any any good and many bad engineers know, NTSC reception > specifies a contour signal level and probability level. Unfortunate because > the best (at the city-grade contour) that NTSC has to deliver is F(50,80). > At the grade A and grade B points, the probability is F(50,50). And, the > inferference contour is F(50,10), wich a desired to undesired dB figure > specified. > > Upshot: for all it's superiority, permitting COFDM would have provided a > superior signal level to that of NTSC, and -- aside from narrow technical > modulation issues -- would have unwound the carelfully (politically) > negotiated replacement of NTSC with an equivalent service level from 8-VSB. > To permit COFDM, broadcasters would have had to pay a heavy price (or prices). > > At least, back then. I don't recall anybody offering to pay the government > money to permit COFDM operations. Might make sense now, if it's so superior. > > John ("i'm glad to see Dermot supporting my 'political' position on COFDM in > the U.S. with empirical data) Willkie > > P.S.: I saw a posting requesting information about the origins of 30-foot > reception criteria. I'm suprised M. Schubin didn't respond; the 30-foot > rule, as I've pointed out here several times) comes from the FCC's R-6602 > (Longley-Rice) study, which, if memory serves me correctly, was first > published in 1946 or so. > > P.P.S. I've also seen postings about Ibiquity/IBOC. Sounds great, an > engineer of long tenure in the industry told me, except for it to work, > Shannon's law has to be repealed, and he pointed out, the folks at Ibiquity > are "real pearls" to work with. > > > > > > > > > > > > > ---------------------------------------------------------------------- > You can UNSUBSCRIBE from the OpenDTV list in two ways: > > - Using the UNSUBSCRIBE command in your user configuration settings at > FreeLists.org > > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word > unsubscribe in the subject line. > > ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.