[time-nuts] Datum FTS 4065B Plot
brooke at pacific.net
Wed May 14 18:39:40 EDT 2008
On 8 May I had been plotting for a number of days and saw a similar line
indicating a frequency offset of 472E-15. So on that date I dialed in an
offset of +472E-15.
For a couple of days the frequency didn't change more than +/- 10ns.
Then on the third day it started the plot you see AND the new slope is about
the same as the old slope i.e. 470E-15. BUT, the frequency offset display
reads 472 (E-15 units). Do you see my dilemma?
See Attached display photo.
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Tom Van Baak wrote:
>> If you look at the plot I attached as a .pdf you can see that the current slope
>> looks like a nice straight line covering almost 4 days so temperature is not a
>> factor. The only factor I can think of is magnetic field. I guess the next
>> step is to rotate the box 90 degrees and see what happens unless there's some
>> other suggestions.
> Since you are plotting phase (not frequency) the nice straight
> line you see simply means you have a frequency offset. This
> is normal and expected with any standard compared to GPS.
> What may be temperature effects are the little wiggles above and
> below the line. You can almost see they form a diurnal pattern.
> If you subtract the frequency offset before you plot, you'll get
> phase residuals, which will reveal patterns in greater detail.
> There are Excel functions that will help you fit lines to the data
> and remove trends, etc. Email me your XLS file offline and I'll
> show you.
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