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.
