[ntp:questions] GPS_NEMA, but high offset and jitter?

unruh unruh at wormhole.physics.ubc.ca
Mon Mar 1 06:35:26 UTC 2010


On 2010-03-01, Kelsey Cummings <kgc at microshaft.org> wrote:
> David J Taylor wrote:
> ...
>> I would knock something up if there were enough interest, but it would
>> be a Windows program so of limited interest to the OP.
>
> That's the idea anyway.  At the time, I was convinced the PPS signal was
> showing clearly and it was but with the led transistor in backwards the
> PPS line was getting pulled down to 1.4v or thereabouts.  Not enough for

Hard to know how it would do that. 

> the serial port to register it.  It would have been useful to have
> something that just watched for the DCD pulse rather than trying to
> figure out what nptd was or was not seeing.
>
> With that fixed, everything synced right up.  Seems reasonably stable
> with jitter at 4ms and offset fluctuating from -4ms to 4ms.  More than
> good enough for our needs.

4ms??? PPS from GPS should be 4usec, a thousand times better! (Or was
that what you meant). 
You could set up whatever was reading the pps to record to syslog every
time it received a pulse. 

>
> -K




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