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.