[ntp:questions] Consumer GPS question

Brian Garrett mgy1912 at cox.net
Tue Feb 6 21:18:33 UTC 2007


<shane-dated-1173382499.fffb68 at cm.nu> wrote in message
news:vR4yh.901457$5R2.849335 at pd7urf3no...
> Hey all,
>
> I am looking at the possibility of using a GPS receiver for NTP time sync
> either via the nmea refclock driver or gpsd, just a little home project.
> From my googling, I've read that the only way to get decent results is to
go
> with an rs232 sync and stay clear of usb or bluetooth.  Looking at the
> mainstream gps sites, I've found the Globalsat br-355 unit and I'm
wondering
> whether this is suitable for NTP sync and what kind of accuracy I should
> expect.
>
>
http://www.buygpsnow.com/globalsat-br-355-water-proof-serial-gps-receiver-si
rf-star-iii-br355-v3-1-1-free-arkon-mount-432.aspx
>
> The device seems to use a ps2 cable which converts via a y-cable into a
db9
> serial connection and gets power from the PS2.  What I can't seem to find
in
> the specs or on the globalsat site is whether the db9 connection provides
a
> PPS output.  If not, are there any PPS capable receivers out there that
> don't require electronics knowhow (soldering etc.)?  That's all I've found
> so far.
>
> Tia,
> Shane

What OS and what kind of receiver?  I've used a handheld on my Windows
desktop with, um, amusing results.  I used PPS, but the NMEA app couldn't
tell whether the pulse belonged to the previous second or the upcoming
second, with the result that I was always one second slow.  Then, of course,
there's Windows' granularity issues, which assured that even with PPS
properly configured I wouldn't have been able to get much below 20 ms.
With a real OS and a dedicated receiver (save the Magellan for hiking), you
ought to get better results than I did--sub-millisecond, I would think.

Brian





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