[time-nuts] How close can you trim a Cs?

John Ackermann N8UR jra at febo.com
Wed Mar 9 12:52:00 EST 2005

Mike S wrote:
> At 10:42 AM 3/9/2005, John Ackermann N8UR wrote...
>>time to stabilize).  The real issue is the noise on the GPS signal, which with 100 second averaging is around 10 nanoseconds with occasional spikes of 20ns or so.  But over several hours you can get a pretty good view of what the slope is -- the question is whether it's good enough to measure parts in the low 13s or even better, high 14s.
> It don't think so, but I'm new to this and what do I know? Check out the data at http://www.boulder.nist.gov/timefreq/service/gpstrace.htm
> Yesterday, for instance, they report Allan Deviation of the GPS system at 2.77 x 10e-13 over a 2:40 averaging period. For 600 second averaging it's in the low 12's. There are days where it takes over 5 hours of averaging for the GPS system to measure at the low 13 level (check March 6). That is, I suppose, exclusive of any other errors which may be introduced in your own measurements (I'd guess they have better measurement stuff than you :-) ).
> Mike, W8UR 

First of all, I'm not sure we can allow both W8UR and N8UR on the same 
list.  Way too confusing... :-)

Thanks for the link.  I haven't been paying attention to the daily 
offsets (and that's a new and improved presentation format over what I 
recall seeing before -- it's really informative and useful) and probably 
I should, though I'm pretty much working with at least 8 and usually 12 
to 24 hours of data before I draw any conclusions, so I don't think the 
GPS system stability is a major factor, at least at the offsets I'm 
dealing with now.


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