Hi Indeed all a time tagger does is spit out picoseconds since some arbitrary start point. Some run on and on forever ( counting up to pretty big numbers in the process). Others roll over at a pre-defined point. You then massage the data to take those out.
I’d suggest that the “software/ firmware included” and “fully debugged” nature of the TAPR TICC make it pretty hard to beat unless you are planning to build a couple dozen …. Bob > On Apr 14, 2020, at 8:11 AM, Tobias Pluess <tplu...@ieee.org> wrote: > > G'day > > OK I see I must do it with time tagging :-) > Is it correct that the time tagging just spits out the time (in ns, for > example) when the rising edge on the A or B input occured? and then, you > calculate the phase by subtracting the time tags for the A channel from the > time tags for the B channel? > Riley also says that DMTD works better with time tagging, so I am not > surprised that you recommend it as well. However I hoped that some simple > measurements (only to get a ballpark figure) would be possible with my > current setup. > In fact, since I read the Riley paper about the DMTD system he built, I > have had my own design on my bucket list since quite a while. I planned to > make my own time-tag counter with two TDC7200 as interpolators, to get ps > resolution, very similar to the TAPR TICC. > > > Tobias > > > On Tue, Apr 14, 2020 at 1:48 PM Bob kb8tq <kb...@n1k.org> wrote: > >> Hi >> >> If the phase slips are “well behaved” they can be handled. The problem >> with a dual channel setup is that they are often not well behaved. The >> period is 100 ns so a frequency drift of 1 ppb will put you in trouble in >> under 2 minutes. >> >> The only real answer is to do it properly and time tag the two outputs. >> Any other approach will get you yelling and screaming at the test set. >> Playing with two counters and not time tagging is in the “yelling and >> screaming” category as well. >> >> Get a TAPPR TICC if you really want to do a DMTD. >> >> Of course you *could* just use a single mixer. That works fine with the >> counter you already have. It will give you an A to B test just like a >> DMTD. The only limitation is the need to tune at least one of the >> oscillators >> in each pair. >> >> There is no requirement that you tune only one. If both are tunable, >> you could tune one to the high end of its range and the other to the low >> end. >> With most OCXO’s, there is plenty of tune range. >> >> Bob >> >>> On Apr 14, 2020, at 2:23 AM, Tobias Pluess <tplu...@ieee.org> wrote: >>> >>> Hey Bob >>> >>> ok now I see your point! you talk about the phase spillovers. Timelab and >>> also Stable32 can correct for them, so it shouldn't be a problem, right? >>> >>> But I agree, if you cannot correct for the spillovers it becomes even >> more >>> difficult. >>> >>> >>> Tobias >>> >>> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq, <kb...@n1k.org> wrote: >>> >>>> Hi >>>> >>>> The gotcha with using a conventional counter (as opposed to a time >> tagger) >>>> is that you never know when things are going to “slip” past each other. >>>> When they >>>> do you get a major burp in your data. Bill’s setup is running a time >>>> tagger …. >>>> >>>> ( = It runs an internal time count, each edge gets “labeled” with a >>>> precise time >>>> stamp that is good to nanoseconds or picoseconds. A Time Interval >> Counter >>>> simply measures the time between edges. That sounds like the same thing, >>>> but >>>> it’s not quite ….) >>>> >>>> >>>>> On Apr 13, 2020, at 6:11 PM, Tobias Pluess <tplu...@ieee.org> wrote: >>>>> >>>>> Hi Bob >>>>> >>>>> Riley suggests to use a single TIC >>>>> >>>>> http://wriley.com/A%20Small%20DMTD%20System.pdf >>>>> >>>>> when you look at the block diagram Fig. 4, you can see that one TIC >>>> allows >>>>> to compare two oscillators. >>>>> I don't know exactly how, though :-) >>>> >>>> The gotcha with using a conventional counter (as opposed to a time >> tagger) >>>> is that you never know when things are going to “slip” past each other. >>>> When they >>>> do you get a major burp in your data. Bill’s setup is running a time >>>> tagger …. >>>> >>>>> >>>>> OK and I see your point on the 8663. I will try to use another >> reference! >>>>> I definitely didn't keep mine on for a long time. I didn't use the >> signal >>>>> generator for a while now, so it was unplugged for a few months. I >> assume >>>>> that's far from optimal for the 10811's stability. >>>> >>>> Best approach is to mount your reference off on it’s own and just power >>>> it. That way >>>> you don’t wear out all the guts of a fancy piece of gear. >>>> >>>> Bob >>>> >>>>> >>>>> >>>>> Tobias >>>>> >>>>> >>>>> >>>>> On Mon., 13 Apr. 2020, 23:53 Bob kb8tq, <kb...@n1k.org> wrote: >>>>> >>>>>> Hi >>>>>> >>>>>>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess <tplu...@ieee.org> wrote: >>>>>>> >>>>>>> Hi Bob >>>>>>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-) >>>>>>> >>>>>>> Maybe I have some good OpAmps for this purpose in my box. I will try >>>> it! >>>>>> of >>>>>> >>>>>> You need something that is quiet (like the OP-37) and has a pretty >> good >>>>>> slew >>>>>> rate. Past that, there are a lot of candidates. The TI OPA-228 family >> is >>>>>> one. >>>>>> >>>>>>> course I saw that my setup was not ideal as there was a bit of noise >> on >>>>>> the >>>>>>> signals which I guess does lead to some jitter in the trigger circuit >>>> and >>>>>>> therefore decreases my measurement noise floor. >>>>>> >>>>>> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 >> good >>>>>> digits. >>>>>> Net result is a measurement that’s good in the vicinity of parts in >>>> 10^-13 >>>>>> >>>>>>> >>>>>>> Can you say something about how it would be done using a TIC? >>>>>>> I don't have two identically good counters, but the HP 5335A could be >>>>>> used >>>>>>> as TIC, couldn't it. >>>>>> >>>>>> The standard way of doing the test is to run two counters / two TIC/s >> / >>>>>> two whatever’s. >>>>>> I know of no practical way to do it with a single 5335. >>>>>> >>>>>>> >>>>>>> And the offset source I used is not directly the HP 10811, but the HP >>>>>> 8663A >>>>>>> Signal generator internally uses a 10811 as reference source. But I >>>>>> didn't >>>>>>> wait for days for it to warm up properly. (Should I?) >>>>>> >>>>>> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of >>>> how >>>>>> you >>>>>> use the 10811, it needs to be on for a while. How long very much >> depends >>>>>> on >>>>>> just how long it’s been off. Best to keep it on all the time. >>>>>> >>>>>>> >>>>>>>> Fun !!! >>>>>>> Yea, of course! :-) >>>>>>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab >> by >>>>>>> myself. I use TimeLab to see what numbers I should expect, and then I >>>>>> want >>>>>>> to compute it all myself in Matlab because I want to see how it >>>> actually >>>>>>> works. ;-) >>>>>> >>>>>> Be careful any time you code this stuff for the first time. It’s >>>> amazingly >>>>>> easy >>>>>> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest >>>> that >>>>>> you should not code it up yourself. I generally do it in Excel or in >> C. >>>>>> >>>>>> Bob >>>>>> >>>>>>> >>>>>>> >>>>>>> Best >>>>>>> Tobias >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq <kb...@n1k.org> wrote: >>>>>>> >>>>>>>> Hi >>>>>>>> >>>>>>>> Ok, first the math: >>>>>>>> >>>>>>>> If your offset oscillator is 10 Hz high at 10 MHz, you have a: >>>>>>>> >>>>>>>> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD >>>>>>>> >>>>>>>> You get to add a 6 to what Time Lab shows you. >>>>>>>> >>>>>>>> If you are getting an ADEV at 1 second of 1x10^-4 then that >> multiplier >>>>>>>> gets you to 1x10^-10 >>>>>>>> >>>>>>>> So, what’s going on? >>>>>>>> >>>>>>>> You can’t feed the mixer outputs straight into a counter. The >> counter >>>>>>>> front >>>>>>>> end does not handle LF audio sine waves very well. You need to do an >>>>>>>> op-amp based limiter. A pair of OP-37’s in each leg ( or something >>>>>>>> similar) >>>>>>>> should do the trick. >>>>>>>> >>>>>>>> Second, the offset source needs to be pretty good. A 10811 tuned >> high >>>>>> with >>>>>>>> both the mechanical trim and the EFC is a pretty good choice to >> start >>>>>> out. >>>>>>>> >>>>>>>> If you only have one counter, simply ignore the second channel. You >>>> are >>>>>> now >>>>>>>> running a single mixer. It still works as a comparison between the >>>>>> offset >>>>>>>> oscillator >>>>>>>> and your DUT. >>>>>>>> >>>>>>>> If you want to do it properly as a DMTD, then you set up two >> counters. >>>>>> One >>>>>>>> to measure mixer A and the other to measure mixer B. Set them both >> up >>>>>> to >>>>>>>> measure frequency. Time tag the data files so you know which reading >>>>>>>> matches up with which. >>>>>>>> >>>>>>>> Fun !!! >>>>>>>> >>>>>>>> Bob >>>>>>>> >>>>>>>>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess <tplu...@ieee.org> >> wrote: >>>>>>>>> >>>>>>>>> Hi again Bob >>>>>>>>> >>>>>>>>> I tried to do some measurements with a DMTD! >>>>>>>>> In my junk box I found a little PCB from earlier experiments on >> that >>>>>>>> topic, >>>>>>>>> with a power splitter and two SRA-3H mixers, it was even already >>>> wired >>>>>>>> for >>>>>>>>> the DMTD configuration. So I gave it a try! >>>>>>>>> As "transfer oscillator" I used my HP 8663A signal generator, and >> set >>>>>> it >>>>>>>>> high in frequency by 10 Hz. To the two mixers, I connected the two >>>>>> 10MHz >>>>>>>>> signals and at the mixer outputs, I put a little lowpass filter >> with >>>>>>>> 100Hz >>>>>>>>> corner frequency. >>>>>>>>> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so >> I >>>>>>>> tried >>>>>>>>> to feed them directly into the HP 5335A TIC and used the TI mode to >>>>>>>> measure >>>>>>>>> the delay between the two signals. >>>>>>>>> This gives 10 readings/sec, which I try to process with TimeLab. >>>>>>>>> It does give some interesting graphs, but I don't know yet how to >>>>>>>> correctly >>>>>>>>> set up TimeLab for this kind of measurement. I.e. now, I get an >> ADEV >>>> in >>>>>>>> the >>>>>>>>> order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that >>>> mean >>>>>> I >>>>>>>>> simply need to multiply this with 1e-7 to get the *real* ADEV at >>>> 10MHz? >>>>>>>>> this would mean that my real ADEV is in the range of 1e-11 to >> 1e-12, >>>>>>>> which >>>>>>>>> is indeed my target value, BUT I expect that things are not that >>>>>> simple. >>>>>>>>> (i.e. what if I didn't set the transfer oscillator high by +10Hz >> but >>>>>> only >>>>>>>>> by 9.9Hz for example). >>>>>>>>> Can you give some hints on that? >>>>>>>>> Of course I also did the noise floor test (i.e. I fed the 10MHz >>>> signal >>>>>>>> into >>>>>>>>> a power splitter and connected the two outputs to my DMTD with two >>>>>>>>> different lenghts of cables. This gave results starting at 1e-4 >> going >>>>>>>> down >>>>>>>>> to 1e-7, maybe it would have gone even lower but I measured only >> for >>>> a >>>>>>>>> couple of minutes.) >>>>>>>>> >>>>>>>>> Can you give some hints on that? >>>>>>>>> >>>>>>>>> Best >>>>>>>>> Tobias >>>>>>>>> HB9FSX >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq <kb...@n1k.org> 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 >>>>>>>>>>> >>>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>>>>>>> To unsubscribe, go to >>>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>>>> and follow the instructions there. >>>>>>>> >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>>>>>> To unsubscribe, go to >>>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>>> and follow the instructions there. >>>>>>>> >>>>>>> _______________________________________________ >>>>>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>>>>> To unsubscribe, go to >>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>> and follow the instructions there. >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>>>> To unsubscribe, go to >>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>> and follow the instructions there. >>>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>> and follow the instructions there. >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>> and follow the instructions there. >>>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.