[ntp:questions] GPS_NEMA, but high offset and jitter?
David J Taylor
david-taylor at blueyonder.co.uk.invalid
Mon Mar 1 09:43:41 UTC 2010
"Kelsey Cummings" <kgc at microshaft.org> wrote in message
news:4b8b4844$0$1956$742ec2ed at news.sonic.net...
> 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
> 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.
In case it's some help, there's a simple serial port LED monitor program
now available here:
It works on my Windows XP system when run as Administrator - no other
testing done, but reports are welcome. NTP must be stopped (and any other
COM port program) while the tester is used. The DCD LED flashes white
when a working GPS is connected.
As Bill comments, I hope your milliseconds are actually microseconds!
Even with Windows, I see well under 250 microseconds offset (depends on
temperature, typically less then 50 microseconds) and less than 10
microseconds jitter (average 3 microseconds) on the XP stratum-1 server.
More information about the questions