Hi > On Jan 18, 2015, at 5:12 PM, Stéphane Rey <steph....@wanadoo.fr> wrote: > > Bonsoir Magnus (Are you in Sweeden ?) > > Being able to measure high stability and low phase noise is definitely a need > for me as I'm trying to design low noise synthesizers and I'm already > reaching the limits of my current tools for phase noise and I can't afford an > E5052 for my own. At work I've one but I will probably not stay after august. > And anyway I need such tools in my lab at home…
If you have tools at work, the best possible thing to do is to get some oscillators / standards characterized. If you *know* what this or that oscillator is doing in terms of ADEV or phase noise at this Tau or frequency offset, it’s much easier to figure a lot of this out. The most basic way to do phase noise in the basement is with a single mixer setup running into some sort of audio FFT device. A sound card can be used or an audio spectrum analyzer. Parts are < $100 to get one setup once you can do the audio measurements. For ADEV, a DMTD or it’s cousin, the single mixer is the easy way to go. The single mixer does not get a lot of discussion these days. It is much easier to set up than a DMTD. It does require an offset oscillator. Once you have a single mixer phase noise setup, you are about half way to a single mixer ADEV setup. Cost for one is < $100 in parts. You already have a counter to collect the data out of it. In both cases you are running a comparison device. Having a characterized OCXO to compare to is a really nice thing. Bob > As low-noise and stable synthetizers depends on the standard used, I need as > well to measure them as well... > > Let's start with this simple experiments and once I will understand the ins > and outs I will try to improve. I know techniques of cross-correlations and > you've already talked about DMTD that for sure I will have to come to... > > Good night > Stephane > > -----Message d'origine----- > De : Magnus Danielson [mailto:mag...@rubidium.se] > Envoyé : dimanche 18 janvier 2015 22:46 > À : Stéphane Rey; 'Discussion of precise time and frequency measurement' > Cc : mag...@rubidium.se > Objet : Re: [time-nuts] question Alan deviation measured with Timelab and > counters > > Bonsoir Stéphane, > > On 01/18/2015 10:34 PM, Stéphane Rey wrote: >> Thanks a lot Bob and Magnus for your very helpful comments. >> >> The HP5370a was indeed in TI mode. By the way what is the difference with >> +/-TI, the button just aside... >> >> But I guess I understand where I've missed something : I've tried to put the >> Rb on channel A and the DUT on channel B but result was always the same but >> I do understand now that there is indeed a switch to change from COMmon to >> SEParate and it was always on COM meaning I believe that channel B wasn't >> used. This explains a lot of things I did not understand. I'm sorry for >> these so basic issues that might have been solved if I had read carefully >> the HP5370a manual first. > > Good. This confirmation makes sense to be and Bob, now we can relax as the > mystery is solved. > >> So possible conclusions until now are that I have actually measured the ADEV >> floor of the system rather than my DUT... which is already nice. The second >> conclusion from these oscillations seen with the GPSDO under test is that >> there is very likely in this GPSDO design a systemic noise added to the 10 >> MHz output (power supply, PCB coupling, ... I'll make further investigations >> on it later on). > > It's a great opportunity to learn the tools, and once you have the tools, you > can see if you can't improve things. > >> I will experiment all the suggestions you made and will come back. For >> information the 1PPS from the HP58503b has a positive pulse width that is >> only few us length. > > This only makes it hard to view on a scope, but long enough to reliably > trigger your counter and scope. > >> Now, when considering that the method is to compare the DUT to an other >> source, I assume then that the other source shall be at least 1 order of >> magnitude better than the DUT. Otherwise this will be impossible to >> distinguish who is the instability contributor between the source and DUT, >> right ? > > For a simple setup, yes. But then we are the time-nuts, we have ways of > handling these things. :) Let's get you started with the basic measurement, > it will be a good start. > >> Then the second question is what kind of very stable source can be used to >> measure DUT which could be Rb or GPSDO which are already in the range of >> 10E-10 to 10E-12 < 100s ? > > Time-nuts tend to spend their time and money getting even more stable clocks > and tools. If you have the right tool, you can measure near and > *under* the noise-level of your reference, but not without running into > issues. One such trick is called cross-correlation, while another is to use > three-corner hat techniques. > > Cheers, > Magnus > > > > --- > L'absence de virus dans ce courrier électronique a été vérifiée par le > logiciel antivirus Avast. > http://www.avast.com > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
