[time-nuts] Thermal impact on OCXO

Scott Stobbe scott.j.stobbe at gmail.com
Mon Nov 7 15:48:47 EST 2016

Another nice plot! It looks like after 2am you see temperature swings of
1.5 degF roughly every 30 minutes? Correspondingly, the EFC line which is
nominally ~2.8vdc sees swings of +-50 uV?

On Monday, 7 November 2016, Bob Stewart <bob at evoria.net> wrote:

> Hi guys,
> First of all, thanks for the additional responses.  I was a bit angry and
> rude yesterday, and I figured this thread was over.  Thanks for staying
> with me.
> I haven't had time to look over the data etc in your responses.  I'll do
> that and get back to the list if appropriate.
> I spoke to Attila and Azelio offline last nite and from their input, I
> decided to hook up the 3456A and collect some data, which is in the plot
> attached.  As usual, I've modified one of my standard plot scripts, so
> there is some extraneous data that wasn't removed.
> First for our purposes is the thin red line, which is the DAC value locked
> at 0x734B0.  The orange trace is the temperature adjusted so that each step
> of 10 on the right hand Y tics is one degree F.  The dark blue trace is the
> EFC value read by the 3456A.  It has been multiplied by 100,000 and then
> had 282600 subtracted.  This leaves just the LSD scaled at 1:1 on the right
> hand Y tics.
> There's something interesting on the far right hand side where the
> temperature goes low and stays there.  The DVM value follows it down, but
> then recovers while the temperature stays down.  I'm not sure what to make
> of this.  Either then OCXO is making up for the temperature change by
> increasing the temperature, or the 3456 is compensating for it after the
> fact.  In either case, the EFC seems to only follow the transient
> temperature changes, and doesn't actually track the temperature on the
> board.
> So, to my eye, after 14 hours, there is only a dependency on thermal
> transients.  I'll leave it running for some time yet, but the EFC doesn't
> seem to be drifting in any meaningful way at this point, other than in
> relation to temperature changes.
> Note:  I used a shielded twisted-pair with the usual clips attached to
> ground and EFC in my GPSDO.  On the 3456, the two leads go to the
> appropriate volts inputs, and the shield goes to the ground input.  The
> "guard" switch is out, which is the off position.  There is no shield
> connector on the DUT side.
> Bob
>  -----------------------------------------------------------------
> AE6RV.com
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info

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