[ntp:questions] Suggested gps devices for use as a time source forntpd

Jason Rabel jason at extremeoverclocking.com
Thu Jul 26 13:33:38 UTC 2007


> I have always wanted to get a gps unit to keep good time independent of
> my internet usage. I have just bought a car and want to get a gps
> navigation unit for it for when I go on long trips and thought I may as
> well kill two birds with one stone and get a navigation system that I can
> use as a ntp time source as well.
> ...
> Now most of the nav units have usb connectors so I assume that's so they
> can be used for this purpose. I gather I also have to look for ones that
> support NMEA or PPS output is this still correct?
> ...
> I would prefer not to have to modify my (ubuntu linux) kernel but
> installing a module is acceptable.

I think Richard's post hit it on the head about navigation vs timing
receivers.

AFAIK, there is no GPS receiver with those little displays for cars that
also has a PPS output.

The Garmin GPS 18 LVC is probably your cheapest route for a PPS capable unit
that is all ready to go. It's an all-in-one device, so you will have to
place it in a window or outside where it can get a clear view of the sky.
Searching some price engines, the lowest price I see is about $60 +
shipping.

You will need to modify your linux kernel to add PPS support, no way around
that. Without PPS support you would get better time via the internet.
Building a new kernel is not that difficult, there are many guides online.
Patching it on the other hand could be a pain depending on how much custom
code there is. An easier alternative is to use FreeBSD or Solaris which
already have PPS support built-in.

What kind of jump in time are you seeing when you saturate your connection?




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