Allow me to apologize to start this again. Bert In a message dated 5/11/2010 7:25:39 P.M. Eastern Daylight Time, warrensjmail-...@yahoo.com writes:
(My apologies to all, this is a game Bruce and I play every time I bring up my simple tester.) Bruce wrote: >"So you now actually integrate/average the frequency over the sampling >interval (Tau) after rejecting the need to do this for months?" Yes, I integrate/average just the same as I have always done it from day one. Did you finally understand how the integration works using most any ADC? Hint: it's done with oversampling the tau zero time. (and a LP filter set to a value above the tau zero but below the oversamping rate) The VERY SAME thing I have been trying to tell you from day one, something that you have chosen to ignore. The very original Block diagram that I posted shows it, if you need more information. ws ******************* Warren So you now actually integrate/average the frequency over the sampling interval (Tau) after rejecting the need to do this for months? Bruce ***************** WarrenS wrote: > Bruce > > Before we go around again and discuses what my simple tester can and > can not do and why, > It would be helpful if you would take the time to better understand > how it works and why it works the way I have done it. > You really should try one yourself if you can't see why it works. > You are going to be surprised and embarrassed at how good it works. > Why you're at it, try the "swing test" with anything you have. Let me > know how that goes. > > I'm not saying that may tester will match someone's Latest ever > changing NEW idea of what the "correct AVAR" should be, > After all it just Logs correct, integrated, Freq difference data of > ANY noise type > and does it without adding any dead time or aliasing all by using > pretty much using ANY ADC capability of over sampling at the tau Zero > rate. > If one then uses the data log with something like the classic Stable > 32 S/W or Ulrich's Plotter, > it gives is the exact same results as other methods costing much much > more, over the whole tau range. > This is limited only be its reference oscillator (Same way that all > others are limited of course, Doesn't get much better than that). > If that is not good enough for you, them you need to discuss the > results with Symmetricon and others that give the same answer as mine, > not me. > > If for some reason you want to set one up wrong so that it matches the > results of some other special instrument, I'd be glad to tell you how > to have it add back in the dead time or aliasing artifact problems or > whatever else you would like it to do wrong, that it presently does > correctly. > > ws > > ****************** > Bruce wrote > > As long as one is aware that your method (as implemented by you) doesn't > actually measure Allan variance, it may be useful for comparing the > relative stability some sources for small Tau (unfortunately the range > of Tau for which the method may produce useful results depends on the > phase noise characteristics of the sources being compared). > To measure AVAR the technique has to have the same response to all phase > noise spectral components as does AVAR. > Since you do not integrate/average the frequency measures the phase > noise response of the method is not identical to that used in > calculating AVAR. > This technique probably works best when white phase noise dominates the > phase noise spectral region of interest (usually for small Tau). > > For those who can follow the theory, the following paper shows how the > above method is affected by aliasing etc: > http://hal.archives-ouvertes.fr/docs/00/37/63/05/PDF/alaa_p1_v4a.pdf > > The paper also shows how the required integration (needed to actually > measure AVAR) can be approximated from the discrete sample sequence. > Alternatively one could avoid the numerical integration by replacing the > ADC with a zero deadtime (ie not a dual slope converter. A multislope > algorithm like that used in the 34401A (but not the 3458A) should work > as the signal is integrated continuously) integrating ADC. One > possibility is to use a VFC as NIST did when they used this technique > some decades ago. > > Of course, the classical DMTD setup undersamples the phase noise > spectrum and thus may suffer from aliasing artifacts. > Such aliasing artifacts have no significant effect when the phase noise > spectrum is flat. > > Bruce > > ********************* > WarrenS wrote: >> For the Really cheap time nuts, >> >> It sounds like Bert Kehren has done a great Job building a Dual Mixer >> tester. >> There are other simpler, less standard ways to get good data for Allan >> Variance and small frequency differences. >> My VERY simple $10.00 analog tight PLL Tester BB (Previously posted) >> pretty much accomplishes the same goals as his, >> and it can do 1e-13 in a second, and 1e-11 in 10ms (limited of course >> by the single reference Oscillator used) >> >> A simple test that most can do at home, and still challenges the best >> high end testers out there is Tom's the swinging Oscillator test. >> http://www.leapsecond.com/pages/10811-g/ >> (The results from my PLL tester is attached) >> >> ws >> >> ****************** >> ----- Original Message ----- From: <EWKehren at aol.com> >> To: <time-nuts at febo.com> >> Sent: Tuesday, May 11, 2010 7:02 AM >> Subject: [time-nuts] Dual Mixer >> >> >>> The Dual Mixer project is nearing completion. >>> Let me refresh every ones memory as to my goals. >>> a) Total cost less than $ 200 >>> b) 1 E-13 with a one second offset >>> c) use parts attainable by every one >>> d) easy to assemble only a few surface mount parts >>> e) a five channel counter that yields 1 E 15 resolution and >>> interfaces >>> directly to a PC via RS232 or USB >>> f) A counter that also gives you instant frequency difference at the >>> sample rate, not only Allan Variance >>> g) Modular so one can use only the Dual Mixer >>> h) Modular so one can use multiple units to do simultaneous >>> comparison of >>> more than two oscillators. >>> i) Isolation between D/M and counter so that the counter can be >>> powered >>> by the PC USB port >>> >>> I am happy to report that all goals have been accomplished, attached >>> is a >>> picture of the D/M, limitation of the file size does not allow me to >>> attach >>> an actual board picture, but if you contact me direct I will send >>> you one, >>> the final board is actually nicer since the first layout had to >>> accommodate >>> several variances. >>> >>> The D/M part leans heavy on the original NIST unit with a few >>> substitutions >>> and recommendations from Bob Camp. Also beside Opto Couplers >>> SN65LVDS1's >>> have been included for those that want to use other counting methods. >>> Selection of filter capacitors allow the use at other offset >>> frequencies such as >>> 10 and 100 Hz. The D/M fits in a standard 74 X 111 X 20 mm Euro case >>> and >>> the counter can be stacked below or next to it using the Opto >>> Isolators as >>> the inter connect. The SYPD-1's fit right on the board but >>> connections are >>> included to use the HP 10514 A. As a matter of fact removing the HP >>> mixer >>> board from its housing fits it nicely on the board and every thing >>> is still >>> inside the housing. >>> The counter will handle 1 an 10 Hz offset with a 1 E 14 resolution >>> at 10 >>> Hz. Thanks to Richard Mc Corkle we have great drawings and code, >>> available to >>> every one. >>> Code, drawings, list of material and PC board layouts and its file, >>> will >>> be available to every one once the project is completed. >>> I need help in the following areas >>> a) help me create a nice set of drawings that are computer generated >>> something I am not able to do >>> b) create the computer program that takes the output of the counter >>> board >>> and allows Allan Variance plots, frequency difference and dual >>> temperature >>> readings and plots using RS232 and USB. >>> c) an independent test by a third party. >>> As I said previously, I am not getting in the business of supplying >>> parts >>> but will work with people that will help achieve the three points >>> listed >>> above. Presently I have boards on order and will have two >>> uncommitted board >>> sets and probably also component kits. >>> Please contact me directly. >>> Again thank you Corby Dawson, Richard Mc Corkle and Bob Camp. >>> Bert Kehren Miami >>> >>> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.