[time-nuts] Good clean-up oscillators

[Bob kb8tq]

Hi

If you take a look at typical TCXO’s and XO’s in a real world environment, their noise is higher than a similar 
OCXO even at 100 Hz. If you are cleaning up something like a Rb, your loop may well be below 1Hz. 

Like everything else, it becomes a “that depends” sort of thing. If your cleanup loop bandwidth is in 
the KHz … it really does not matter. In the 30 to 300 Hz range it’s a bit of a tossup. By the time you go
below 10 Hz, a good OCXO will always win. 

Yes, this is all based on the Rb cleanup example that would be in the 10 MHz vicinity. Go up to 300 MHz
and everything shifts a bit. Yet another “depends”. 

Bob

> On Jan 23, 2019, at 3:43 PM, Magnus Danielson <magnus at rubidium.se> 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?
> 
> Cheers,
> Magnus
> 
> 
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