--- Jack Smith <[EMAIL PROTECTED]> wrote:
> That was true at one time, but is it still the case? I recall reading
> that with the switch to digital video distribution color burst is
> locally generated and hence not tied to the NBS standards.
>
>
> Jack K8ZOA
NBS Special Publication 432 used to describe this method back in the late 70s,
early 80s, but as was pointed out, it is no longer valid.
Personally, I have a homebrew 10 digit frequency counter (99% complete)
combined with a homebrew frequency reference locked to WWVB (60 kHz) (also 99%
complete) which is used as a timebase for the counter. I can measure WWV and
CHU's HF signals, and resolve the Doppler shift that occurs as the signals from
these stations propagate via the ionosphere. :-)
I have discovered that AM radio stations that carry IBOC digital broadcasts
have generally VERY accurate and stable carrier oscillators. Some are based on
Rubidium oscillators tied to GPS clocks!
If you use this method for testing / calibration, just make sure you're
receiving groundwave (not skywave) because of the Doppler effects earlier
described.
73, de John, KD2BD
Visit John on the Web at:
http://kd2bd.ham.org/
.
.
.
.
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