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

Richard B. Gilbert rgilbert88 at comcast.net
Thu Jul 26 13:06:44 UTC 2007

Kurt Häusler wrote:
> Hi,
> I have been running ntpd for ages now as a timekeeper for my network, its
> pretty accurate but I download a lot and saturate my dsl line which I
> believe causes the time to be less accurate than when the line is idle.
> So 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.
> I was looking for recommendations and found a few old lists of dedicated
> gps time sources and was wondering what is available now.
> 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.
> Any suggestions for gps nav units that support ntp on linux?
> Thanks

GPS receivers designed for navigation do not make very good timing 
receivers.  Navigation receivers are optimized for navigation.  Timing 
receivers are optimized for timing and usually have a PPS output which 
marks the exact instant that matches the time the receiver is telling 
you about.

The USB interface is NOT well suited to timing applications!  You should 
try to get one with an RS-232 interface plus a PPS output.

The Garmin GPS18LVC is an inexpensive timing receiver.  You will need to 
  add a 5V power supply and an RS232 connector of appropriate size and 
gender to connect it to your computer.  Some soldering required!

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