Hi A single mixer compares two devices. Provided you can offset the frequency of one of your devices, it does exactly what you need to do.
Bob > On Apr 3, 2020, at 7:56 PM, Tobias Pluess <[email protected]> wrote: > > Hey Bob > > hmm how would a *single mixer* design look like? in the end I need to > compare *two* clock signals, so a single mixer won't be of much use, would > it? > > Tobias > > On Sat., 4 Apr. 2020, 01:51 Bob kb8tq, <[email protected]> wrote: > >> Hi >> >> A *single mixer* setup is something that can be done quickly and easily. >> The *dual mixer* setup brings in a bunch of issues that are far more >> easily handled on a good PCB layout. >> >> Either way, it is going to work far better with the right sort of low noise >> ( = single digit nanovolt per root hz …) op amps than with whatever >> you happen across first …. >> >> Bob >> >>> On Apr 3, 2020, at 7:38 PM, Tobias Pluess <[email protected]> wrote: >>> >>> Hi Bruce >>> >>> I have some TUF-1 mixers in my junk box as well as some JFET OpAmps >> AD8626. >>> So, if I connect the OpAmps appropriately with some diode limiters as you >>> suggest, would you say this would give an acceptable DMTD system? >>> If so it sounds like something that can easily be built on a breadbord or >>> in manhattan style, as Bob already mentioned. That would be really cool. >>> I think a while ago I asked a question which goes in a similar direction >> - >>> which mixers are better as phase detectors (to build a PLL for phase >> noise >>> measurement) and which ones should be used as actual mixers (like in this >>> case). >>> >>> >>> Tobias >>> HB9FSX >>> >>> On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths, <[email protected] >>> >>> wrote: >>> >>>> One can merely add diodes to the opamp feedback network form a feedback >>>> limiter and maintain the opamp outputs within the range for which the >> opamp >>>> is well behaved whilst maintaining the increase in slew rate for the >> output. >>>> >>>> Bruce >>>>> On 04 April 2020 at 04:26 Tobias Pluess <[email protected]> wrote: >>>>> >>>>> >>>>> Jup, some of them even have phase reversal when they are overloaded, so >>>> it >>>>> is perhaps not a good idea in general, but I think there are opamps >> which >>>>> are specified for this. >>>>> >>>>> Tobias >>>>> >>>>> >>>>> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow <[email protected]> >>>> wrote: >>>>> >>>>>> Caution: opamps make terrible limiters- their overload behavior is >>>>>> generally ugly >>>>>> and unpredictable. It's much better to use a genuine level >>>> comparator, and >>>>>> wire it >>>>>> up so that it has a modest amount of hysteresis. >>>>>> >>>>>> Dana >>>>>> >>>>>> >>>>>> On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq <[email protected]> wrote: >>>>>> >>>>>>> Hi >>>>>>> >>>>>>> The quick way to do this is with a single mixer. Take something like >>>> an >>>>>> old >>>>>>> 10811 and use the coarse tune to set it high in frequency by 5 to 10 >>>> Hz. >>>>>>> >>>>>>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio >>>> tone. >>>>>>> That tone is the *difference* between the 10811 and your device under >>>>>>> test. >>>>>>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz. >>>>>>> >>>>>>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very >>>> small >>>>>>> shift >>>>>>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the >>>> change >>>>>>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X >>>> increase ). >>>>>>> >>>>>>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s >>>> not >>>>>>> that >>>>>>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1 >>>>>>> second. >>>>>>> >>>>>>> The reason its not quite that simple is that the input circuit on the >>>>>>> counter >>>>>>> really does not handle a 10 Hz audio tone as well as it handles a 10 >>>> MHz >>>>>>> RF signal. Instead of getting 9 digits a second, you probably will >>>> get >>>>>>> three >>>>>>> *good* digits a second and another 6 digits of noise. >>>>>>> >>>>>>> The good news is that an op amp used as a preamp ( to get you up to >>>> maybe >>>>>>> 32 V p-p rather than a volt or so) and another op amp or three as >>>>>> limiters >>>>>>> will >>>>>>> get you up around 6 or 7 good digits. Toss in a cap or two as a high >>>> pass >>>>>>> and low pass filter ( DC offsets can be a problem ….) and you have a >>>>>>> working >>>>>>> device that gets into the parts in 10^-13 with your 5335. >>>>>>> >>>>>>> It all can be done with point to point wiring. No need for a PCB >>>> layout. >>>>>>> Be >>>>>>> careful that the +/- 18V supplies to the op amp *both* go on and off >>>> at >>>>>>> the >>>>>>> same time …. >>>>>>> >>>>>>> Bob >>>>>>> >>>>>>>> On Apr 3, 2020, at 5:13 AM, Tobias Pluess <[email protected]> >>>> wrote: >>>>>>>> >>>>>>>> hi John >>>>>>>> >>>>>>>> yes I know the DMTD method, and indeed I am planing to build my own >>>>>> DMTD >>>>>>>> system, something similar to the "Small DMTD system" published by >>>>>> Riley ( >>>>>>>> https://www.wriley.com/A Small DMTD System.pdf). >>>>>>>> However I am unsure whether that will help much in this case, >>>> because >>>>>> all >>>>>>>> what the DMTD does is to mix the 10MHz signals down to some 1Hz >>>> Signal >>>>>> or >>>>>>>> so which can be measured more easily, and I already have 1Hz >>>> signals >>>>>> (the >>>>>>>> 1PPS) which I am comparing. >>>>>>>> Or do you suggest to use the DMTD and use a higher frequency at its >>>>>>>> outputs, say 10Hz or so, and then average for 10 samples to >>>> increase >>>>>> the >>>>>>>> resolution? >>>>>>>> >>>>>>>> Thanks >>>>>>>> Tobias >>>>>>>> HB9FSX >>>>>>>> >>>>>>>> >>>>>>>> On Fri, Apr 3, 2020 at 12:53 AM John Miles <[email protected]> wrote: >>>>>>>> >>>>>>>>>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what >>>> resolution >>>>>>>>> does >>>>>>>>>> my counter need? If the above was true, I would expect that a 1ps >>>>>>>>>> resolution (and an even better stability!) was required to >>>> measure >>>>>> ADEV >>>>>>>>> of >>>>>>>>>> 1e-12, The fact that the (as far as I know) world's most recent, >>>>>>>>>> rocket-science grade counter (some Keysight stuff) has "only" >>>> 20ps of >>>>>>>>>> resolution, but people are still able to measure even 1e-14 shows >>>>>> that >>>>>>> my >>>>>>>>>> assumption is wrong. So how are the measurement resolution and >>>> the >>>>>> ADEV >>>>>>>>>> related to each other? I plan to build my own TIC based on a >>>> TDC7200, >>>>>>>>> which >>>>>>>>>> would offer some 55ps of resolution, but how low could I go with >>>>>> that? >>>>>>>>> >>>>>>>>> That sounds like a simple question but it's not. There are a few >>>>>>>>> different approaches to look into: >>>>>>>>> >>>>>>>>> 1) Use averaging with your existing counter. Some counters can >>>> yield >>>>>>>>> readings in the 1E-12 region at t=1s even though their single-shot >>>>>>> jitter >>>>>>>>> is much worse than that. They do this by averaging hundreds or >>>>>>> thousands >>>>>>>>> of samples for each reading they report. Whether (and when) this >>>> is >>>>>>>>> acceptable is a complex topic in itself, too much so to explain >>>>>> quickly. >>>>>>>>> Search for information on the effects of averaging and dead time >>>> on >>>>>>> Allan >>>>>>>>> deviation to find the entrance to this fork of the rabbit hole. >>>>>>>>> >>>>>>>>> 2) Search for the term 'DMTD' and read about that. >>>>>>>>> >>>>>>>>> 3) Search for 'direct digital phase measurement' and read about >>>> that. >>>>>>>>> >>>>>>>>> 4) Search for 'tight PLL' and read about that. >>>>>>>>> >>>>>>>>> Basically, while some counters can perform averaging on a >>>>>> post-detection >>>>>>>>> basis, that's like using the tone control on a radio to reduce >>>> static >>>>>>> and >>>>>>>>> QRM. It works, sort of, but it's too late in the signal chain at >>>> that >>>>>>>>> point to do the job right. You really want to limit the bandwidth >>>>>>> before >>>>>>>>> the signal is captured, but since that's almost never practical >>>> at RF, >>>>>>> the >>>>>>>>> next best thing to do is limit the bandwidth before the signal is >>>>>>>>> "demodulated" (i.e., counted.) >>>>>>>>> >>>>>>>>> Hence items 2, 3, and 4 above. They either limit the measurement >>>>>>>>> bandwidth prior to detection, lower the frequency itself to keep >>>> the >>>>>>>>> counter's inherent jitter from dominating the measurement, or >>>> both. >>>>>>> You'll >>>>>>>>> have to use one of these methods, or another technique along the >>>> same >>>>>>>>> lines, if you want to measure the short-term stability of a good >>>>>>> oscillator >>>>>>>>> or GPSDO. >>>>>>>>> >>>>>>>>> -- john, KE5FX >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> time-nuts mailing list -- [email protected] >>>>>>>>> To unsubscribe, go to >>>>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>>>> and follow the instructions there. >>>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> time-nuts mailing list -- [email protected] >>>>>>>> To unsubscribe, go to >>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>>> and follow the instructions there. >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> time-nuts mailing list -- [email protected] >>>>>>> To unsubscribe, go to >>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>> and follow the instructions there. >>>>>>> >>>>>> _______________________________________________ >>>>>> time-nuts mailing list -- [email protected] >>>>>> To unsubscribe, go to >>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>> and follow the instructions there. >>>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] >>>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>> and follow the instructions there. >>>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
