Hi yes sure I agree that it is hard to beat. But from a commercial perspective, any hobby is more or less nonsense - the same is true for my own GPSDO. I just could have bought one and would be finished. But making my own is more interesting ;-) I'll see whether I buy a TAPR TICC. Maybe it would come in handy to have something I can compare with.
Tobias On Tue., 14 Apr. 2020, 14:27 Bob kb8tq, <kb...@n1k.org> wrote: > 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. > _______________________________________________ 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.