[time-nuts] 10 MHz OCXO recommendations

Neil Schroeder gigneil at gmail.com
Wed Nov 12 15:28:19 EST 2014


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 <mark at 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 <csteinmetz at 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 at 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 at febo.com <javascript:;>
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


More information about the time-nuts mailing list