); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY From: "Tom Van Baak" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] FMT on October 13 Date: Tue, 25 Sep 2007 23:45:12 -0700 Message-ID: <[EMAIL PROTECTED]>
> ); SAEximRunCond expanded to false > Errors-To: [EMAIL PROTECTED] RETRY > > > 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 > > The jitter on a single period is likely very, very high, especially > if it comes over the air. That's why one usually measures over > a duration of thousands or even millions of periods (effectively > called the gate time). > > The HP 53132A makes something like 200,000 measurements > per second. As a result, for a certain range of frequencies, it > claims 12 digits/sec of resolution (vs. HP 5370 ~11 digits/sec). As was discussed recently, didn't they do averaging such that they updated value every second but the raw singel-shot resolution doess not give you the 12 digits/sec. There was a nice explanation in an article on how this was not improving say ADEV measurements in the end. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
