); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I just wanted to point out that with reciprocal counters, you can get resolution much better than the 1Hz/s you would get with conventional frequency counters, even though the actual accuracy of the measurement may be way off.
The original question seemed to imply that with a short transmission time, you could not guarantee a frequency accuracy of 1e-6 Hz, which you probably can't anyhow, but the limit is not the resolution of the instrument or the measurement method. I do not know how far off calibration my HP 5370s are, but the 20pS resolution is at best only usable under some circumstances that I have not isolated yet, due to jitter. When measuring a 3.5 MHz signal (@1dBm) from my HP 8657B through 1 meter of good coax cable (with counter and generator phase locked to the Thunderbolt GPSDO) in Frequency mode with a 1s gate time, the resolution is 1e-5Hz, with about 1e-3Hz p-p variation. When measuring over 1 period with 10,000 periods sample size, the resolution is only 1e-1Hz with a standard deviation of ~400 Hz (or about 0.1%). Of course, over the air, it will be much worse due to noise, let alone propagation, fading and multipath. Didier KO4BB > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak > Sent: Wednesday, September 26, 2007 1:45 AM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] FMT on October 13 > > > 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). > > /tvb > > > _______________________________________________ > 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. _______________________________________________ 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.
