[time-nuts] How close can you trim a Cs?
John Ackermann N8UR
jra at febo.com
Wed Mar 9 09:42:44 EST 2005
I've been going nuts trying to trim my 5061A versus GPS. I have it well
within 1x10e-12, but trying to get down into the low 13s is proving
challenging. Making C fields adjustments of a couple of minor divisions
that according to the book should be result in a shift of a few parts in
10e-13 don't seem to have the effect they ought to; in some cases the
frequency seems to move in the opposite direction.
For example, I did a run that showed about +3x10e-13 and tweaked four
minor divisions (nominally 3.2x10e-13 according to the book), which
should have brought it down to nearly flat. Instead, the offset
increased to about +6x10e-13. So, I adjusted the eight minor divisinos
back (so I ended up the at same shift, but opposite direction from the
starting point). Now, I'm reading +7x10e-13!
It may be that I'm being too impatient and not letting the comparison
(against raw GPS 1pps) run long enough, but when after 15 hours I'm
seeing a plot that shows a pretty stable slope, it's hard not to assume
that things need more tweaking!
So maybe the first question is -- at these offsets, how long should I
track against GPS before making a tweak? And the second question is, at
what point am I tweaking in the noise -- how close is it realistic to
aim for with this class of standard?
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