[time-nuts] Good clean-up oscillators

[jimlux]

On 1/23/19 12:43 PM, Magnus Danielson wrote:
> Fellow time-nuts,
> 
> While we often look at long-term stability, ADEV etc. we consider 
> oscillators in their free-running properties. This is all fine and dany, 
> but when we want to use an oscillator as a clean-up oscillator, the 
> servo-loop with surpress much of the low-frequency/high-tau properties 
> and replace that with that of the reference.
> 
> Consider for instance that we have a LPRO rubidium and we want to use a 
> clean-up oscillator to provide better phase-noise, what would be a good 
> selection?
> 
> While there is plenty of choices, it is a bit different from that which 
> is relevant when considering it as a free-running oscillator. The white 
> noise which dominated far-out would dominate, and only some of the 
> flicker phase becomes relevant.
> 
> I could easily get a OCXO of good quality, but really, what would be 
> interesting choices? Have someone measured this enough to get a kind of 
> rough idea at least?
> 

My idea was to get an OCXO without the oven (or with the oven disabled) 
- the idea was that an OCXO will have high Q for good phase noise, and I 
can deal with the frequency shift due to frequency and aging in the long 
term in other ways

As it happens, it's hard to do in practice (it makes your unit more 
"custom") because OCXO mfrs don't conveniently bring out oven and 
oscillator power separately.

So it's probably not available as a standard item, but you could 
probably get an SC cut crystal and put it in your own circuit.