This is my setup:
I am using a Navilock NL-320U connected to a small Linux box running ntp
4.2.4p4-44.1 that came with the openSuSE 11.0 distribution. This is
supposed to supply a time service to the local network without the use of
external network ntp servers purely from the received GPS signal.
I know that using a USB connection is not optimal, but the achieved accuracy
is fine for my needs.
Last Saturday (2008-08-02) I noticed for the first time that the time off
the GPS unit was one second behind the DCF time, which I monitor on a
separate radio clock. A reboot of the system did not help. On Sunday
(2008-08-03) everything was back to normal. I noticed the same effect again
on Friday evening (2008-08-08) and through yesterday (2008-08-09), but
everything seems fine today (2008-08-10).
I added a network server to my ntp configuration to double check the effect.
This is how the output "ntpq -p" looks like when everything is fine:
remote refid st t when poll reach delay offset
jitter
==============================================================================
LOCAL(0) .LOCL. 10 l 19 64 377 0.000 0.000
3.906
*GPS_NMEA(0) .GPS. 3 l 22 64 377 0.000 14.902
3.906
xptbtime2.ptb.de .PTB. 1 u 422 1024 377 66.375 -8.106
5.216
And this is the output when I observe the one second lag:
remote refid st t when poll reach delay offset
jitter
==============================================================================
LOCAL(0) .LOCL. 10 l 33 64 17 0.000 0.000
3.906
*GPS_NMEA(0) .GPS. 3 l 30 64 17 0.000 -978.27
11.515
xptbtime2.ptb.de .PTB. 1 u 31 64 17 67.160 1.002
3.906
Looking at the raw NMEA output, the UTC info in there also seems to be one
second slow.
In all of this I presume the PTB time to be correct.
My question is, has anyone else observed this and how can I fix this?
Thanks
Harald
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