[time-nuts] 1 pps correction

Hal Murray hmurray at megapathdsl.net
Sat Mar 31 21:44:26 UTC 2012


martyn at ptsyst.com said:
> I’ve seen that the peak to peak jitter is reduced from something like 27 ns
> to < 10 ns.

> Is this a reduction of just the jitter, or is the actual accuracy to UTC
> also improved by this amount. 

Have you read the hanging-bridges paper?
  Tom Clark and Rick Hambly: Timing for VLBI
  http://gpstime.com/files/tow-time2009.pdf
I think that is the key to understanding this area.

If you could average over many sawtooth cycles, you should get an accurate 
answer.

The problem is that you don't get to pick how many cycles fit into your 
averaging time.  The sawtooth pattern is the beat between two frequencies.  
One of them is drifting with time/temperature.  If you are unlucky, the beat 
frequency can be very very low.

The sawtooth correction lets you correct on a cycle-by-cycle basis.  You 
don't need to average over many samples.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.






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