[time-nuts] Phase noise vs warmup or time

John Ackermann N8UR jra at febo.com
Tue Dec 29 21:37:54 UTC 2009


Tom Van Baak said the following on 12/29/2009 04:24 PM:

> 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.

As a practical matter, you need to allow an OCXO time to stabilize or 
else the warm-up frequency drift may cause difficulties in the phase 
noise measurement.  You need to keep the DUT and reference in the proper 
phase relationship, and if the drift is too fast the PLL may not be able 
to keep up.  From what I've seen using the TSC test set, you'll get 
glitches in the flicker-noise region (say, around 1 Hz offset); the 
floor isn't much affected.

I fully agree with Tom on the main point -- I'm not talking days or 
weeks, but an hour or so is probably a good idea.

John



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