[ntp:questions] NTP server with Garmin GPS 18 LVC

Adrian P ntp at pascalau.ro
Wed Dec 18 19:59:03 UTC 2013

> In addition to what the others have suggested, does you GPS 18 LVC have
> a good view of the sky?  It's nothing like as sensitive as the newer 18x
> LVC (note the "x").
> If it helps to compare, the data from my own Intel Atom FreeBSD 8.2
> system is here - PC Pixie:
>    http://www.satsignal.eu/mrtg/performance_ntp.php
> As it's plotted with MRTG it's only sampled at 5 minute intervals, and
> the droop in the yearly graph is an artefact of MRTG's summarising, it's
> not real.  My GPS 18 LVC is mounter on the roof, sloping towards the
> west at an angle of about 22 degrees and slightly sheided by adjacent
> houses, so not a 360 degree view, but not inside either.

Hi David,

Thanks for the great site!

I just noticed that mine is actually a GPS 18x LVC, as written on its
back. It is temporary located on the inside window sill, in my
apartment at the 3rd floor. So it can see only half of the sky,
through the window. Later I plan to install it on the roof, but first
I need to figure out how to route the cable outside of my apartment
(need to drill one hole I suppose :).

>From your graphs I could see that the best time keeper is the
Raspberry Pi #1, running Linux/3.6.11 and the Adafruit MTK3339 indoors
RX. Do I read them correctly?

Everywhere is written that FreeBSD is the best OS for time keeper,
since its kernel supports nanosecond accuracies. However, if GPS 18x
LVC PPS signal has only microsecond accuracy, then I suppose there is
no point on using FreeBSD, any linux would be okay as well. So what do
you think, looking from NTP point of view only, is this nanosecond
accuracy the only reason why someone would use FreeBSD, or there are
some other reasons as well? I see you have experience with all kind of

Many thanks,

More information about the questions mailing list