[ntp:questions] question about logs of PPS

Christian Pinedo Zamalloa christian.pinedo.zamalloaNOSPAM at NOKKgmail.com
Wed May 16 11:36:01 UTC 2007

On 2007-05-15, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> The Motorola M12+T is specified to deliver its Pulse Per Second output 
> with the leading edge within 50 nanoseconds of the top of the second. 
> Getting that into your computer is where the problem lies.  Things like 
> cable length can be compensated for.  Interrupt latency is more 
> difficult because it's difficult to determine exactly what value you 
> need to compensate for.  Depending on interrupt priorities and what else 
> is going on, the latency may not even be constant.
> I'd say that you are probably within one microsecond of the correct time 
> if you are using the Motorola M12+T as a reference clock.

So my offset is very bad, i have peaks of milliseconds. I have done
several graphics with gnuplot and i have put them available at:


At 15 i restarted several times the NTP daemon but today (16) i haven't
touch the server.

I think that the graphics are very bad and this could be by various

1. The GPS aerial is in the roof inside a plastic water bottle to protect from
rain. I have seen that the bottle has too much adhesive tape that could
difficult the GPS to find satellites. I will remove the excess.

2. I don't know how my compains obtained the GPS coordinates. I will
run WinOncore during a week to check the latitude, longitude and height.
Could a bad value of these parameters produce a unstable GPS clock??

3. The Motorola M12 board is near other electronic components: wifi
access point, printer, PC, ... Could these components perturb the clock

Thanks for your comments and if i get a better behavior of the clock
signal i will post to the group,

Christian Pinedo Zamalloa

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