Just to add a note on the original question : there are some brand new never used Vectron 8091s available for a reasonable price now and it's drift and jitter have been on par with my Wenzel.
I am not yet set up to measure it's phase noise or other general rf characteristics but according to its cut sheet they're quite good. On Tuesday, November 11, 2014, Mark Spencer <m...@alignedsolutions.com> wrote: > Sorry a few more points to mention. > > If for some reason I am particularly concerned about the stability of an > OCXO reference I will compare it to another OCXO and on occasion to a GPSDO > as well while measuring a "Device Under Test." This gives me some comfort > that if am looking at the performance of a particular "Device Under Test" > that any drift in the OCXO I am using as a reference would have been > detected. (It also gives me a reason to keep my stack of HP5370 and > HP5335 counters running.) I don't expect this approach to give me absolute > certainty of picking up drift or jumps in my reference but it does give me > some comfort. > > While I suspect this approach would not go over very well in a commercial > lab vs buying a high performance cesium standard or H Maser (: for hobby > use it seems to work for me. Timelab is also useful for collecting > analyzing the data from the various counters. I also trigger all the > counters from the same 1pps source. > > I typically compare my "best" OCXO's to my "best" GPSDO on a more or less > continuous basis (from a time nuts perspective it's of some interest to > look at their long term drift.) From time to time I also cross check my > "best" GPSDO against another GPSDO (: > > Regards Mark Spencer > > Sent from my iPad > > On 2014-11-11, at 4:26 PM, Charles Steinmetz <csteinm...@yandex.com > <javascript:;>> wrote: > > > Mark wrote: > > > >> I find the concept of occasionally adjusting a good OCXO which in turn > is used as a reference works well for me. I have some that haven't > needed adjustment for over 2 years (they are still well within one part per > billion of being on frequency.) > > > > A few of us have advocated this approach on the list, and there is good > reason for it. A GPSDO offers two advantages: (1) it is self-adjusting, > therefore easy to own and use; and (2) it has better stability at long tau > than the OCXO alone. The price you pay for those advantages is poorer > stability at low tau than the OCXO alone, which can be anywhere from slight > with a good design (e.g., Thunderbolt, Z3801) to shockingly bad with a bad > design (including many DIY attempts). > > > > If one does not need the very best performance at long tau -- and most > time-nuts do not -- a free-running OCXO that you adjust manually every now > and then can be the best reference available to the average time nut. > ("Long tau" can be anywhere from 100 seconds to several thousand seconds, > depending on the particular OCXO.) Plus, not spending money on GPS > discipline allows you to spend more on the OCXO to get better stability at > low tau, and a more extended upper limit on "low" tau (say, better than GPS > all the way to 2000 seconds instead of 200 seconds). > > > > Personally, I do use GPS discipline to keep my best OCXO in "perpetual > adjustment," but that is mostly for convenience. Usually, I turn > disciplining off when I'm taking data. Only when I'm doing something where > the data are averaged for longer than about 3000 seconds do I leave it on > (3000 seconds is based on the stability of my particular OCXO). > > > > Remember, GPS has a well-defined stability floor, and is not better than > a good OCXO at averaging times (tau) less than 100 or even 1000 seconds -- > so GPS discipline cannot do anything to help the stability of a good OCXO > at shorter tau than that. (Yes, it may be able to help a lousy OCXO or > TCXO at lower tau -- but you can get a better OCXO than that for $20, so > why bother?) There is so much focus on GPSDOs that I think many time nuts > do not realize this fundamental fact. > > > > A few rules of thumb: > > > > -- An OCXO is the best low-tau reference most amateurs can afford > > -- GPS discipline cannot help at low tau because it is noisy > > -- Most of us do not need extreme stability at long tau > > > > And some general conclusions: > > > > -- Get the best OCXO you can find > > -- Enclose it (thermally isolated from the enclosure) > > -- Don't try to whip a so-so OCXO into shape with GPS discipline > > > > Finding a really good OCXO may take some effort. Some models are more > likely to be "really good" than others (like the BVA that Mark mentioned, > and some others that have been vetted in large numbers), but even then > there can be large differences from sample to sample. So, one may need to > sort through a number of them to find a "really good" one. If one doesn't > have access to a clearly better oscillator for comparison, using the > "three-cornered hat" technique with one's best oscillators is probably the > best method available to the amateur time nut. Note that quartz > oscillators tend to exhibit best stability if they are left on > continuously, and stability may improve for a long time (months, perhaps > even many months) after they are turned on, depending on how long they were > off and how much trauma they received before being powered up again). > > > > The point is that GPS discipline is not always (and maybe, not usually) > the best way to get the best stability possibile over the range of tau that > is most important to amateur time nuts. Further, it takes very > well-designed GPS discipline to improve things at long tau without making > them worse at shorter tau, so GPS discipline can easily be a net negative > (particularly since most of us do not need extreme stability at very long > tau). So, a good OCXO that is manually adjusted from time to time as > required will likely have the best stability most amateur time nuts can > obtain, at the range of tau that is actually important for the applications > to which it will be put. > > > > Best regards, > > > > Charles > > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com <javascript:;> > > 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 <javascript:;> > 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.