[time-nuts] OCXO Advice

[Bob Quenelle]

I’d like some advice about the OCXO’s I’m using. They’re UCT 108663-10, double oven, purchased from the auction site. The attached graph shows the frequencies of 2 very similar circuits compared to the 10 MHz output of an LPRO-101. At 7.6 hours, the blue line design switches from GPS PLL to hold mode. The red line design is still in GPS PLL (not equipped with hold mode) and it’s not fair to compare the blue line noise to the red line noise after 7.6 hours. Prior to 7.6 hours, comparison shows the blue line design has more noise. Both OCXO’s have 100’s of hours of use and were on for about 50 hours prior to what shows in the graph.  I don’t know if the range of slow noise I see from both OCXO’s is typical. Any other choices for OCXO that would be quieter and affordable?

I measured the frequency control voltage at the OCXO pins and found it stable within 100 uV. Scale factor of the OCXO is about 0.9 Hz per V or 0.9 mHz per mV and the drift would require more control voltage drift than what I see. I also checked the 12 V supply to the OCXO and found it stable within 100 uV. Both OCXO’s are similarly mounted. Looks like ambient temperature is a factor.

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