Hi, On 2020-03-08 16:15, jimlux wrote: > On 3/8/20 1:52 AM, Magnus Danielson wrote: >> >> The Allan intercept is really where the cut-over from reference Allan >> plot to the steered oscillator plot. The concept of Allan intercept is >> actually not perfect science, but a concept. The actual physics would >> make the cut-over analysis on the phase-noise plots make more sense, but >> for the time-constants we talk, that's where the Allan deviation plot >> has taken over typically. Actually doing the cut-over in Allan deviation >> form carries with it biases values, making the Allan intercept value >> biased. It gets you to the right neighborhood, sure, but do expect a few >> trims for optimum stability. >> > > > The conceptual idea being similar to setting a PLL Loop filter > bandwidth such that the reference noise (multiplied up) and the VCO > noise are the same at that point? > Yes, that's where the term intercept comes from. > Of course, it's "easy-ish" for a crystal oscillator (flat noise > spectrum at crossover) and VCO (steadily declining spectrum at > crossover) and those noise spectra remain the same (ish). In theory simple yes. > > I think the "art" comes in picking the right gains and bandwidths, > because of things like GPS has diurnal variations, temperature > variations (also diurnal, but also faster with HVAC turning on and off)
Which is the reality with a number of systematic disturbances which is not random noise. Such concerns takes over, and the Allan deviation intercept is even further from modeling that correctly. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
