[time-nuts] Re: Low Phase Noise70 10 MHz bench signal source sought

[Bob kb8tq]

Hi

Rb and low phase noise ( at least far removed ) are sort of mutually 
exclusive specs. You need to pick one … 

Assuming the decision is to go for the -170 dbc/Hz spec, Congratulations 
you are buying on OCXO. Not quite clear which OCXO, but it’s pretty likely
to be an OCXO. (Yes, there are exceptions, but they are rare enough to be 
in the “don’t bother” category), 

Next step would be to decide on the max offset that needs to cut in at. 
100 Hz is into the “crazy/ not gonna happen” region. 1KHz is unlikely. 
10 KHz is doable. 100 KHz relaxes things a bit. 

While the “buy a bunch and test” approach works for things like ADEV, 
it probably isn’t the best approach for this spec. If you buy a bunch of this
or that OCXO, their 10KHz phase noise *should* be pretty consistent. 
Sorting to get 2 db … nope, not worth it.  It *is* a pretty good bet that 
a commercial spec at 10K will be beat by 3 to 6 db. 

What to buy? Head off to the spec sheets on whatever you see on eBay
and make some guesses. 

Bob





> On Apr 1, 2022, at 5:12 PM, Joseph Gwinn <joegwinn at comcast.net> wrote:
> 
> I'm looking for suggestions for AC-powered 10 MHz sinewave laboratory 
> signal sources with very low phase noise, having a noise floor below 
> -170 dBc/Hz.  Rubidium is desired, but not essential.  Reliability 
> and durability in lab use is essential.
> 
> Which makes and models should I consider purchasing?  
> 
> I like the SRS model FS725, but its noise floor is too high at -150 
> dBm/Hz, 20 dB noisier than many things I may wish to measure.  
> <https://www.thinksrs.com/products/FS725.htm>
> 
> Thanks,
> 
> Joe Gwinn
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