[time-nuts] FMT on October 13

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Sep 25 00:04:00 EDT 2007

Didier Juges wrote:
> I guess it depends on signal to noise ratio. With reciprocal counters, you
> only need one period to measure as acurately as you need, but to have good
> acuracy, you need very good S/N, as there is no filtering possible. 
> For example, the HP 5370 can measure a single period of a signal with a
> resolution of 20pS (excluding noise and trigger imperfections), so excluding
> these errors, the HP 5370 could measure a single period of a ~3.5 MHz signal
> with 7 x10-5 precision (if I have not goofed the calculations....) More
> periods improve the resolution proportionately to the quare root. Accuracy
> is another matter.
> Didier KO4BB

With band limited gaussian noise and an SNR of 40dB the rms error in
measuring the period of a single cycle is about 0.3%


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