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.
