[time-nuts] OCXO retrace, how long is reasonable?

[Matthias Welwarsky]

Dan,

I've attached the last 25000 seconds of data. The drift was about 15 DAC units 
during this time. It's a 16 bit DAC, the pulling range is about 10Hz, so LSB 
is worth 1.5e-4 Hz. 15 DAC units are 2.3e-3 Hz over 25000 seconds.

Looking at your graph, it seems it took about  a week to express a slowdown in 
drift, and maybe a month in total to sort of settle in? That's encouraging, 
maybe I just need to give it a bit more time.

My temperature graph shows that there's some correlation, but not pronounced 
enough to explain the behavior. The sensor is not thermally coupled to the 
OCXO.

BTW, the MDEV graph is mislabeled. It shows the DAC, not the TIC.

Regards,
Matthias
On Freitag, 4. September 2020 19:29:33 CEST Dan Kemppainen wrote:
> Matthias,
> 
> How about a 'quick and dirty, hand wavey' graph?
> 
> This is a known 'kinda good' OCXO, that was off for about a year. The
> DAC values are just that, DAC counts.  The black line should represent
> about 8e-12 per day drift. (Sorry, I don't have better numbers than that
> easily on hand). I think it's about 4uHz per count, or so.
> 
> Note 1: The first 13700 seconds of data were thrown away. That drift was
> astronomic. (Basically vertical on this scale!)
> 
> Note 2: Also, note that this only one retrace, of one trimble OCXO.
> 
> Note 3: Notice the dates on the bottom of the graph. This is around 6
> months of worth of drift. Small tics are 7 days apart, major tics 3 weeks...
> 
> Hopefully this helps!
> 
> Dan
> 
> On 9/4/2020 12:00 PM, time-nuts-request at lists.febo.com wrote:
> > Message: 3
> > Date: Fri, 04 Sep 2020 08:50:21 +0200
> > From: Matthias Welwarsky<time-nuts at welwarsky.de>
> > To:time-nuts at lists.febo.com
> > Subject: [time-nuts] OCXO retrace, how long is reasonable?
> > Message-ID:<5901813.EksvcnS80i at linux-5fgm.suse>
> > Content-Type: text/plain; charset="us-ascii"
> > 
> > Hi,
> > 
> > I mentioned in a previous email that I seem to have picked a particularly
> > bad (broken?) OCXO for GPSDO testing. It drifts at a very high rate, from
> > the DAC graph I calculate it is around -4e-4 Hz/hour. It's been on for
> > about 1 week now and the drift doesn't seem to come down, or maybe just
> > marginally.
> > 
> > Of course, this being a surplus OCXO with unknown history, odd startup
> > behavior is somewhat expected but so far I haven't seen anything this
> > drastic.
> > 
> > Could this be OCXO retrace? How long can that phase last? I'm trying to
> > decide if I should give it another week or just scrap it and move on.
> > 
> > Regards,
> > Matthias

-------------- next part --------------
A non-text attachment was scrubbed...
Name: graph.png
Type: image/png
Size: 113936 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20200904/0f2d2c27/attachment.png>