[time-nuts] Phase noise vs warmup or time

[Magnus Danielson]

Tom Van Baak wrote:
>> If I have several crystals and I want to find the ones with good phase 
>> noise, do I have to let them run in their ovens for a week/month, or 
>> can I just turn them on and measure the phase noise?
> 
> I'll make a distinction between time domain and frequency
> domain measurements.
> 
> A long warm-up is helpful if you want to measure frequency
> stability (e.g., sigma of tau, or ADEV).
> 
> But, depending on the equipment you use, a phase noise
> measurement (e.g., script L of f) doesn't require the source
> to be long-term stable; you get pretty much the same phase
> noise results in the first minute as you would a day or week
> later.

I agree fully, but the first minute of operation can for some designs 
have significantly higher phase-noise. Discovered that for one 
oscillator of lesser quality. Viewed it with a spec with a fairly wide 
sweep (to get fairly quick update rates) which is sufficient to see the 
noise level decrease as it runs. I suspect it takes time for the signal 
level in the oscillator to stabilize, but that is to be expected.

Cheers,
Magnus