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
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