Hi Ulrich: The SR620 has a 1 kHz Reference output that's derived from the 10 MHz external clock input. It also has a Gate/Arm function.
Appendix B in the PRS10 Manual explains how to use these two features to make 1,000 time interval measurements per second thus averaging the 20 ps one shot way down. http://www.prc68.com/I/PRS10.shtml The time interval armed 1,000 times per second and the difference between zero crossings of a pair of 10 MHz signals are measured. So the range of measurement is 100 ns before rollover. I think at least one of the test signals needs to be 10 MHz to drive the external clock input to get the 1 kHz reference. But you could use Toms PIC divider to generate a 1 kHz signal from about any test signal and use the same method. http://www.prc68.com/I/FTS4060.shtml#SR620Fast http://www.prc68.com/I/TandFTE.shtml#SR620 Have Fun, Brooke Clarke http://www.prc68.com/P/Prod.html Products I make and sell http://www.prc68.com/Alpha.shtml All my web pages listed based on html name http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam Ulrich Bangert wrote: > Martyn, > > 2 parts in 10E-12 in a second's gate time would require to measure the > time interval with an 2 ps resolution. Since the SR620 (at least mine) > features a 20 ps single shot resolution, i fear your number is more > likely "20 parts in 10E-12". Or what you are doing is to make >= 10 > measurements / s of phase and computing the arithmetic mean of them. > > There are not really many companies to offer you direct sub-picosecond > measurement resolution and if at all the devices may in the same price > reigion as your company's boxes. There ARE some measurement schemes that > enable you kind of "artificial magnification" of the time differences to > be measured, for example the Dual Mixer Time Difference Method. In > principle they all look VERY EASY and may give you the impression that > you can make measurements with that on the kitchen table. I have tried > out a few of them just to find out that they do indeed work (in > principle) but that their technical realisation has some strange > requirements that are not too easily given on standard workbench. > Nevertheless I am still working on the problem using a not so well known > proposal. > > Best regards > Ulrich Bangert > > >>-----Ursprungliche Nachricht----- >>Von: [EMAIL PROTECTED] >>[mailto:[EMAIL PROTECTED] Im Auftrag von Martyn Smith >>Gesendet: Mittwoch, 7. Mai 2008 18:52 >>An: [email protected] >>Betreff: [time-nuts] Measuring 10 MHz accurately. >> >> >>Hi, >> >>Two questions for all of you today. >> >>1st Question >> >>I can measure 10 MHz frequency to an accuracy of about 2 >>parts in 10E-12 in >>a one second gate time. >> >>I use a SR620 time interval counter and make a timeAB measurement. >> >>I make two measurements of phase (between my UUT and my >>reference) and then >>calculate the frequency. >> >>I have some nice software that controls the SR620 and does >>all the math. >> >>I'm sure most of you understand my measurement technique, >>since it's as old >>as the hills. >> >>Does anyone have a good application note explain this >>standard procedure? >>I'm trying to explain it to a friend, and can't find a nice >>application note >>with some diagrams, formulas etc. I know HP did one and >>Standard did as >>well, but can't find any quickly. >> >>2nd Question. >> >>I really need to measure 10 MHz to an accuracy of 1 part in >>10E-13 / second >>(ignoring the accuracy of my workshop standard). I've tried >>multiplying the >>10 MHz to the GHz frequencies, but never manage to improve on >>the technique >>I mention in my first question. >> >>Any ideas for a relatively cheap way of doing this. I >>actually represent a >>company that can measure to parts in 10E-15 in one second, >>but their boxes >>costs $50k. >> >>Best Regards >> >>Martyn >> >> >> >> >>_______________________________________________ >>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. > _______________________________________________ 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.
