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 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.
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. 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?) > 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. ;-) 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.