[time-nuts] On some pitfalls of the dual mixer time differencemethod of horology

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Oct 1 07:05:00 EDT 2006


In message <000001c6e547$554bd670$03b2fea9 at athlon>, "Ulrich Bangert" writes:

>> All the repeated steps of amplification/limiting to find the =
>> zero crossing can be almost entirely replaced by a a single FFT.
>
>If dsp methods are a choice one can even do better (at least for simple
>sines) as described by Mr. Greenhall in
>
>www.tmo.jpl.nasa.gov/progress_report/42-121/121G.pdf
>
>The clue here is that not only the zero crossings and its surroundings
>are used for interpolation but ALL samples are used for a comlete signal
>reconstruction and noise removement. For a simple sine this is of course
>easier done as for the more complex Loran-C signal. =

That is exactly what the FFT does for you.

Loran-C is not that much more tricky, it has a well defined
frequency spectrum as well.  Not as simple as a sine-wave, but
well defined all the same.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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