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Re: Mostly Jitter Related

There are many different kinds of jitter.

Signal correlated, signal related, random, operation or subsystem related, etc.

It is possible that the signal correlated jitter might be continuous enough and steady enough WITH A STEADY SINE WAVE SIGNAL to be seen as an IM type of side band on a spectrum analyzer, but the FM of the orginal recorded tone will create a continuously changing Frequency Modulation of that original tone, and by definition, the actual frequency will be varying at any given moment, the sidebands as they show up on a spectrum analysis represent the end points (maximum frequency swing) of the FM portion of the signal, and thus, are a secondary representation of what is actually occuring: a signal being walked all over the time domain.

With any other form of jitter, the non-continuous behavior of the jitter will create time distortions that are constantly changing with each data sample clocked out at the DAC. Yes, some of those may appear to have repetitive components that will then show up as IM sideband end points on a SA around a primary original tone, but since they are occuring on a sample by sample basis, and the SA can only look at a large discrete chunk of time for each analysis, the SA display is more misleading than helpful. You can not FFT one sample.

The measurement is not the reality, just an attempt to lock one portion of the reality into a convenient and familair frame of reference. Do not let all of that make it seem as if the measurement has become the reality.


Jon Risch

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