[ntp:questions] Too much offset from GPS?

Unruh unruh-spam at physics.ubc.ca
Fri Mar 7 23:14:01 UTC 2008


Steve Kostecke <kostecke at ntp.org> writes:

>On 2008-03-07, Hal Murray wrote:

>>ATTRIBUTION MISSING 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 127.127.20.0 mode 1 prefer minpoll 4
>>>server  127.127.1.0 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.



>Perhaps that doesn't matter in your application.




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