Electronics > Beginners

Measuring an OCXO - or not

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metrologist:
I managed to acquire a Wenzel large can OCXO. Unfortunately, it does not have a tuning pin, just an adjusting screw, so I probably will not be able to use it for a GPSDO. Although, I think moving supply voltage will move the frequency too, within limits...

I wanted to verify the aging so have a Trimple UCCM GPSDO referencing my counter. It takes a 10 seconds gate to read mHz. I am recording the reading every 24 hours, starting after a few days after adjusting close to 10MHz.

I used page 12 as a reference: http://freqelec.com/oscillators/understnding_osc_specs.pdf

Is this method going to give me any useful information? Looks like the aging is approaching 4E-10/day, using a log trendline projecting 2 periods.

jpb:
The OCXO probably has better Alan Deviation over 10 seconds than the GPSDO so it seems a pity to take your measurements over just 10 seconds every 24 hours.
If you have a counter that can automatically take reading or allows a very long gate then I'd try taking average frequency over a day rather than 10 seconds, the GPSDO should be approaching 10^-12 or better averaged over a day and you should get a smoother measure of the drift as with luck temperature effects will average out over 24 hours for the OCXO.

Have a look at Bill Riley's page - it has some very interesting publications to down load and his software is now free as well:

http://www.wriley.com/

metrologist:
The counter takes 10 seconds to make a single reading with this many digits enabled. I took a reading once a day at the same time for 10 days.

I thought I would have to take a reading for every 10 second gate, and average all 8640 readings over the 24 hour period. I don't have a GPIB interface yet, so I'm wondering if this is all useful?

edpalmer42:
What kind of counter do you have?

The best way to measure Allan Deviation is to use a time interval counter.  Channel A goes to the GPSDO 1 PPS output.  Channel B goes to the DUT.  Measure the time from the start of the 1 PPS to the start of the next cycle from the DUT.  Depending on how good your DUT and counter are, you might need a high-performance sine to square converter.  Make sure that the counter isn't averaging multiple measurements.  Log the data via RS-232, GPIB, USB, whatever.  Either analyze the data later, or if you have software that supports your counter, you might be able to do it real-time.

Ed

metrologist:
Counters are HP5385A and HP5314A. I don't think either one can do A to B counts here as I don't think the first does it and the second I think is limited in frequency.

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