[ntp:questions] Too much offset from GPS?

Unruh unruh-spam at physics.ubc.ca
Sat Mar 8 15:46:17 UTC 2008

isw <isw at witzend.com> writes:

>In article <Z_jAj.87237$C61.22584 at edtnps89>,
> Unruh <unruh-spam at physics.ubc.ca> wrote:

>> Steve Kostecke <kostecke at ntp.org> writes:
>> >On 2008-03-07, Hal Murray wrote:
>> >>
>> >>>I have problem with my stratum1 box. My box include: freebsd
>> >>>5.2-RELEASE without PPS , ntp-4.2.0_1, Intel Pentium III, 40 G IDE,
>> >>>Germin GPSmap60 , connect with serial com. In GPSmap60 set as NMEA.
>> >>>Freebsd box can get NMEA input string. My configuration of ntp.conf
>> >>>like this:
>> >>>
>> >>>server mode 1 prefer minpoll 4
>> >>>server minpoll 5
>> >>
>> >> Most NMEA devices (or at least all the ones I've worked with)
>> >> send their text with a significant offset.
>> >It gets even better ... NMEA sentences are output by the GPS device
>> >when it is not busy. This means that there is no fixed relationship
>> >between the top of the second and the NMEA sentence. And there will be
>> >significant jitter.
>> Ie, NMEA is good for getting the second, not for getting any better
>> accuracy (well maybe 1/10 sec) If you want accurate time get a gps with PPS
>> output.
>> Otherwise there is no advantage of NMEA over a network ntp connection.

>Well, except for the "no wires" part...

Then buy a gps with ppm. The GPS18LVC is only about $60. And you get
microsecond accuracy rather than 1/10 sec.


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