We use Dual Mixer 10 Hz offst but also Adret and Tracor 10 000 X multipliers along with HP53132ABert Kehren
In a message dated 2/20/2020 3:15:17 PM Eastern Standard Time, kb...@n1k.org writes: Hi For most good standards, all a frequency counter is measuring at a 1 second gate is the floor of the counter: A typical counter might have a 100 ps rms sort of “gate error” at 1 second. That means that the best it actually can do is 100 ppt = 1x10^-10. A good oscillator will have an RMS count to count error of around 10 to 100X better than that. If you set the counter to a 100 second gate time, it still has the same 100 ps sort of error. Now that error is at 1x10^-12. The error in the counter and the 100X better “good oscillator” error now are roughly the same. In any measurement setup, you would prefer your instrument errors to be 5 to 10X *less* than what you are trying to measure. For a 1x10^-12 measurement, you would like the counter to contribute < 2x10^-13 and better yet, to contribute < 1x10^-13. To hit a 1x10^-13 sort of “contribution” your 100 ps counter would need to be set to a 1,000 second gate time. Yes, this assumes that the reference to the counter good enough to stay out of the way at all these tau’s. If the reference contributes, then that also needs to be figured in to the mix. If your counter is in the 400 ps range, that makes things more difficult. If it is in the 20 ps range that makes it a bit easier. There is a bit of hand waving in the above analysis simply to keep it simple. Despite that the basic conclusions are pretty darn close. ===== So if you *do* want to accurately measure <1x10^-12 at a 1 second tau, what counter do you use? Well, you can’t do it with any counter that I am aware of. You need to use a different device or a different technique. The DMTD is one of several approaches that could be used. http://www.wriley.com/A%20Small%20DMTD%20System.pdf <http://www.wriley.com/A%20Small%20DMTD%20System.pdf> https://white-rabbit.web.cern.ch/documents/DDMTD_for_Sub-ns_Synchronization.pdf <https://white-rabbit.web.cern.ch/documents/DDMTD_for_Sub-ns_Synchronization.pdf> https://www.osti.gov/servlets/purl/1494164 <https://www.osti.gov/servlets/purl/1494164> A Phase Station is another way to get the job done: http://jackson-labs.com/index.php/products/phasestation_signal_source_analyzer <http://jackson-labs.com/index.php/products/phasestation_signal_source_analyzer> A TimePod / 3120 also would do the trick: https://www.microsemi.com/product-directory/phase-noise-and-allen-deviation-testers/4131-3120a <https://www.microsemi.com/product-directory/phase-noise-and-allen-deviation-testers/4131-3120a> Even with one of those fancy devices, you still need a *reference* that is “good enough” to do your measurement. All any of the devices above do is compare sources. With multiple sources, you can do some fancy math. The pitfalls of doing that have been mentioned in a number of posts here on the list. The basics: http://www.wriley.com/3-CornHat.htm <http://www.wriley.com/3-CornHat.htm> http://www.miles.io/PhaseStation_53100A_AN_53100A_2.pdf <http://www.miles.io/PhaseStation_53100A_AN_53100A_2.pdf> And off the deep end :) : https://www.researchgate.net/publication/314137002_Three-cornered_hat_versus_allan_covariance <https://www.researchgate.net/publication/314137002_Three-cornered_hat_versus_allan_covariance> (and on and on …..) Bob > On Feb 20, 2020, at 1:40 PM, Taka Kamiya via time-nuts > <time-nuts@lists.febo.com> wrote: > > I have a question concerning frequency standard and their Allen deviation. > (to measure Allen Dev in frequency mode using TimeLab) > > It is commonly said that for shorter tau measurement, I'd need OCXO because > it's short tau jitter is superior to just about anything else. Also, it is > said that for longer tau measurement, I'd need something like Rb or Cs which > has superior stability over longer term. > Here's the question part. A frequency counter that measures DUT basically > puts out a reading every second during the measurement. When TimeLab is well > into 1000s or so, it is still reading every second; it does not change the > gate time to say, 1000s. > That being the case, why this consensus of what time source to use for what > tau? > I recall reading on TICC, in time interval mode, anything that's reasonably > good is good enough. I'm aware TI mode and Freq mode is entirely different, > but it is the same in fact that measurement is made for very short time span > AT A TIME. > I'm still trying to wrap my small head around this. > > --------------------------------------- > (Mr.) Taka Kamiya > KB4EMF / ex JF2DKG > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
