[time-nuts] How can one measure ADEV of a good oscillator?

Bob Camp kb8tq at n1k.org
Mon Dec 1 19:30:57 EST 2014


Hi

> On Dec 1, 2014, at 7:23 PM, Richard (Rick) Karlquist <richard at karlquist.com> wrote:
> 
> On 12/1/2014 4:08 PM, Bob Camp wrote:
> 
>> 
>> Others did a similar thing by simply taking production OCXO’s to the limit of their EFC range. That let you do a coarse sort to find some number of “likely” units. Next step was to pop  a few of them open and short this or that out to get a reasonable beat note. Numbers in the 10 to 20 Hz range were pretty common. After that a single mixer setup followed by a simple limiter got things good enough to screen the production lots.
>> 
>> Bob
>> 
> 
> I am fairly sure they would have done that if it was workable,
> to avoid special crystals.  One rather huge problem with a
> 10 Hz beat note is that you are never going to measure ADEV
> at short (<1 second) sample times that way.

Correct. 

The technique was used for 1 second  and longer ADEV screening. That’s what most of the specs were based on. Tight numbers at < 1 second were rarely seen. For what ever reason, phase noise stopped at 1 or 10 Hz and ADEV went from 1 second out to longer tau. 

Bob

> 
> Rick N6RK
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