[ntp:questions] Very large jitter and offsets on GPS ref clock after upgrade to "p5"

David J Taylor david-taylor at blueyonder.co.uk.invalid
Wed Feb 8 17:45:09 UTC 2012


"David Lord" <snews at lordynet.org> wrote in message 
news:gnbbu8-qne.ln1 at me6000g.home.lordynet.org...
[]
> I've not put a scope on the pps but I added an extra section
> of cable from my Sure GPS, 18 m of 4 x pair telephone cable.
> I will need that length to reach from the GPS down to my PCs.
>
> In the process the offset jumped from 0.004ms to about 12ms
> but fairly quickly went back to a few usec.
>
> PC = me6000 (VIA ME6000), NetBSD-5, ntpd 4.2.6p5
>
> From my ntp-stat file:
> time     offset(ms)
> 15:06        -0.004
> 15:12         0.000
> 15:18         0.001
> 18:24         0.006   extra 18 m cable added
> 15:30       -12.938
> 15:36        -3.672
> 15:42        -0.814
> 15:48        -0.186
> 15:54        -0.054
> 16:00        -0.012
> 16:06        -0.006
> 16:12        -0.002
> 16:18        -0.002
> 16:24        -0.001
>
>
> David

David,

I suspect that the offset jump was purely from losing the PPS signal, and 
nothing to do with the extra cable as such.  BTW: I think your editing 
accidentally included the time - from 15:24 to 18:24.  Must have had "18" 
on the brain!  <G>

My comments on wiring are as before - use one line from each pair as 
ground, and then the other four "active" lines become TXD RXD PPS and +5V 
power.

Cheers,
David 



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