> 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".
One example is 73.622(g), which addresses the case where you have an NTSC
station on the lower-adjacent channel, then the pilot is 5.082138 MHz above
the video carrier of that lower-adjacent NTSC video carrier (including any
offset it may have).
Other not-by-rule cases where the pilot frequency may be purposely choisen
to be something other than 309.440559 kHz above the bottom of the channel
usually are done for other reasons to avoid or minimize co-channel
interference, whether it's DTV-to-DTV or DTV-to-NTSC.
--- Jeff WN3A
