[time-nuts] Thermal impact on OCXO

Bob Stewart bob at evoria.net
Sat Nov 5 19:39:35 EDT 2016

Hi Hal,

With a 20 bit DAC, even a small aging rate is going to show up.  I'll let the one GPSDO cook for a month or so and see what it shows then.  I'll also pull the data from the log file and see if I can see any correlation between the temperature and the EFC over time.  IOW, for data points separated by 3.5 days, does the temperature difference between the two point seem to play a large part of the change in the recorded DAC value.

The graph was made from the logging data sent to the PC.  But, the firmware doesn't have access to historical data on the PC, so something is needed for aging calculations.  Tom mentioned here recently about the 58503A GPSDO saving 64 hours of data for it's aging calculations.  So, I just added a few hours to that to get to 3.5 days of history in the GPSDO.
Bob -----------------------------------------------------------------


      From: Hal Murray <hmurray at megapathdsl.net>
 To: Bob Stewart <bob at evoria.net> 
Cc: Hal Murray <hmurray at megapathdsl.net>
 Sent: Saturday, November 5, 2016 6:23 PM
 Subject: Re: [time-nuts] Thermal impact on OCXO
> The OCXO has been hot for a number of months.

Then I don't understand why it is still aging that much.

> I changed the firmware to save the DAC voltage every 30 minutes for 3.5
> day

That's not very long.

How did you make the graph?  You had to get the data out to a place where you 
can plot it somehow.  If you can do that, why are you "saving" the data?  I 
assume you have a serial port to a PC or something like that.

> The fuzz in the temperature line is, indeed, the HVAC cycling

You could try putting a box over the unit to see if that slows down the 
temperature changes.

Mostly, you are trying to block air flow.

These are my opinions.  I hate spam.


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