[ntp:questions] Too much offset from GPS?

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Fri Mar 7 08:36:01 UTC 2008


>   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.

You can correct that with
  fudge 27.127.20.0 time1 xxxx
where xxxx is the offset to add in seconds.

I forget the sign.  You can work it out by trial and error.

>    remote           refid      st t when poll reach   delay   offset  jitter
>==============================================================================
>*GPS_NMEA(0)     .GPS.            0 l    -   16    3    0.000   -7.127   7.982
> LOCAL(0)        73.78.73.84      5 l   22   32    1    0.000    0.000   0.002
> time.symmetrico .GPS.            1 u   21   64    1  248.084  167.016   0.002
> time.nist.gov   .ACTS.           1 u   20   64    1  273.165  156.541   0.002
> andromeda.cs.pu .CDMA.           1 u   19   64    1  295.742  157.582   0.002
> 203.185.69.60   .PPS.            1 u   18   64    1  270.912  292.165   0.002
> 122.154.11.67   .INIT.          16 u    -   64    0    0.000    0.000 4000.00

It looks like you are off about 160 ms.

What I would do is use the "noselect" option on the server
command on your NMEA line, and adjust the time1 fudge factor
until it looks good.  (Then turn off noselect.)

If you like collecting data and makeing graphs, look into the
statistics options.

-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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