[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

pisteoff at start.no pisteoff at start.no
Wed May 27 19:42:13 UTC 2009


On 27 Mai, 21:21, "David J Taylor" <david-tay... at blueyonder.not-this-
part.nor-this.co.uk.invalid> wrote:
> piste... at start.no wrote:
> > After first trying the Haicom HI-204III claiming to have PPS in the
> > manual without really having it, I bought a Garmin 18x LVC and
> > connected it to the onboard COM-port (COM1) on my Asus M3N78 PRO
> > mainboard. The Haicom is residing on a USB serial adapter (COM6) to
> > check how stable the offset is.
>
> > Running ntp4.2.5p175-win-x86-bin configured with a couple of
> > timesources it seems like my ISP's NTP-server gets "disqualified".
> > Before setting up my own ref.clock I used to have ntp.online.no as my
> > "favorite NTP-server" thinking it would be the best / most local
> > server, but now I might offer them to use me as a clock-source? ;)
>
> > Anyone wishing to see on their own, might check with ntpq
> > solbakken.dyndns.org   What kind of accuracy is expectable with a NMEA
> > GPS with PPS connected to the DCD-line of the serial port? It's not
> > that I have any special need for extreme accuracy, but I suppose it's
> > allright having the most accurate clock in the neighborhood. :)
>
> > Cheers,
> > Geir F
>
> Geir,
>
> I typically see an offset within 0.2 milliseconds using a direct
> connection:
>
>  http://www.satsignal.eu/mrtg/feenix_ntp_2.html
>
> With USB I would see within about 0.5 milliseconds.
>
> Both are much better than an Internet-based time source.
>
> Your Haicom has an offset of nearly 0.5s, suggesting that you might be
> using the wrong edge of the PPS signal.
>
> Cheers,
> David– Skjul sitert tekst –
>
> – Vis sitert tekst –

The 0,5s offset has a quite logical explanation - the claimed PPS
doesn’t exist. There simply aren't enough wires in the cable and I
have also checked with oscilloscope on the spare connectors inside the
unit, and as good as every soldering point inside, but no PPS... Quite
disappointing since the manual claims it has PPS, and I also see clear
indications where inside the GPS the PPS-signal is "supposed to be". I
suppose all that's needed is a firmware to activate the PPS output,
but my mail to Haicom has never been answered. If anyone has good
contacts at Haicom, please let me know! :)

Now I'm just curious how stable the offset is compared to my PPS GPS.
At least the stable part of the offset is possible to configure away,
but guess it's still far away from PPS when it comes to jitter...The
0,5s offset has a quite logical explanation - the claimed PPS doesn’t
exist. I have checked with oscilloscope on the spare connectors inside
the unit, and as good as every soldering point inside, but no PPS...
Quite disappointing since the manual claims it has PPS, and I also see
clear indications where inside the GPS the PPS-signal is "supposed to
be". I suppose all that's needed is a firmware to activate the PPS
output, but my mail to Haicom has never been answered.




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