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 <[email protected]> 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 <[email protected]> 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, <[email protected]> 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 <[email protected]> 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, <[email protected]> wrote: > >>> > >>>> Hi > >>>> > >>>>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess <[email protected]> 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 <[email protected]> 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 <[email protected]> > 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 <[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 > >>>>>>>>> > >>>>>>>> > >>>>>>> _______________________________________________ > >>>>>>> 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.
