[time-nuts] Fw: Fwd: Re: Thermal impact on OCXO

Bob Stewart bob at evoria.net
Mon Nov 7 16:35:58 EST 2016

My friend and mentor Dan Kemppainen's posts apparently aren't making it to the list so I thought I'd forward this one.

-------- Forwarded Message --------
Subject:     Re: Thermal impact on OCXO
Date:     Sun, 06 Nov 2016 12:00:23 -0500
From:     dan at irtelemetrics.com

For what it's worth, Some data from a few of Bob's units:

This is the EFC data for 4 separate units over the last 1120 Hours. 
Since the EFC ranges are different for some of the oscillators, the EFC 
value has been converted to uHz for each unit. The uHz is more 
meaningful to me on the same graph.

Interestingly the Grey and Yellow traces exhibit quite a bit of wander, 
but a linear best fit puts them nearly flat. Although basically 
meaningless numbers the linear fit is at 8e-14 and 3e-15 in this graph. 
Now, these units do exhibit a somewhat high correlation between 
temperature and DAC change, but that data isn't handy right now. It's 
sort of buried here, as these are long term graphs.

The Green trace looks pretty nice, even if you consider the 1.3e-12 per 
day drift. This unit has basically no correlation between DAC and 

The orange trace, well lets just say this oscillator may get replaced 
someday. It exhibits both exhibits a high DAC to temperature 
correlation, and long term drift. It just won't settle down.

As best as I can determine from these units the temperature dependence 
and long term drift is mostly from the oscillator. The long term drift 
of the EFC appears to be minimal as does the thermal drift of the EFC 
circuit. However as Bob Camp and others have pointed out is is not 
trivial to measure such things, so take my conclusions with a grain of salt.


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