[time-nuts] Frequency error -> Parabolic Time Error?

John Ackermann N8UR jra at febo.com
Sat Apr 9 18:32:46 EDT 2005

Brooke Clarke wrote:

> Hi:
> Suppose that my reference oscillator is offset from 10.0 MHz by some 
> small amount.  If I plot the time interval between the reference 
> oscillator and a GPS 1 PPS what will the plot look like over a long 
> time period, a parabola?
> Have Fun,
> Brooke
If it's a stable offset, you should see a straight line with a linear 
slope.  If there's drift (ie, aging), then you'll get a parabola (and if 
there are a couple of things going on, you may get a more complex 
pattern yet).  Usually, the frequency offset is by far the largest 
component of the phase plot, so removing it makes any drift much more 
visible; for that reason I recently updated my stable-stats program to 
plot both the raw phase and the phase with linear offset removed.


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