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.