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 :-) 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. 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.