At 9/5/2009 21:20, you wrote: > > OK, now that NTSC video is gone, so are my handy local video > > carriers that > > I used to use to check the frequency accuracy of my signal > > generators. However, I understand that there are pilot > > carriers buried > > within the 8VSB DTV signals that can be used for the same purpose. A > > couple of Google searches revealed that DTV ch. 7 is supposed > > to have a > > pilot at 174.310 MHz. Putting my old FM-10 on 174.310 & > > listening to the > > beat signal on my R-100, I heard a heterodyne of ~500 Hz. I > > thought that > > error was a bit high, so checked a few other DTV pilots (186.310 & > > 198.310). Interestingly, they were off by the same amount. I > > moved the > > FM-10 to 15 MHz & checked it against WWVH; heterodyne was > > ~1.5 Hz, equating > > to ~18 Hz @ 180 MHz, not ~500 Hz. My best guess is that the > > ATSC pilots > > are actually 309.450 kHz above the bottom of each channel, > > and the 310 kHz > > reference is an approximation. > > > > Can anyone confirm the above? > > > > Bob NO6B > >You're trying to make it easier than it is Bob :-) > >Normally it would be 309.440559 kHz above the bottom of the channel. That's >a real big "normally".
OK, thanks. Well as long as they don't change with the seasons... I took a closer look at chs. 7, 9, 11 & 13 today. I see 7 at 174.309450, 9 at 186.309441, 11 at 198.309730 & 13 at 210.309716. Since the errors between the frequencies are not linear, I suspect that they're either some exceptions to the normal freq., or possibly just loose freq. tolerances. Bob NO6B
