[ntp:questions] help with setting up NTP on windows with a USB GPS

jack j.jack.wang at gmail.com
Fri Nov 27 14:12:30 UTC 2009


You assumed right. I did start with a USB emulated port. The GPS I
bought is from U-Blox and it has both USB and serial output. The
serial output has the 1PPS signal (with an LED indicator). I thought I
would start with the USB output since it's rather hard to find a
computer with a serial port. Also I would like to see the accuracy by
using the USB port only. I later switched to a machine with a serial
port and started using the serial output of the U-Blox GPS device and
1PPS. My objective is to use two of these devices to sync two separate
computers to within ms so they can share time-sensitive data (time

I left the device running overnight and I noticed it computed an
offset at one time. It's currently not updating (everything is zero
now). I will read carefully what Dave Hart said and follow his advice.

Thanks to everyone for your help.


On Nov 27, 1:51 am, "David J Taylor" <david-tay... at blueyonder.not-this-
bit.nor-this-part.co.uk.invalid> wrote:
> "jack" <> wrote in message
> news:9db25657-9837-4ebe-ab32-ce15ae968af8 at j35g2000vbl.googlegroups.com...
> > David,
> > I only have the following in the configure file:
> > server minpoll 4 prefer
> > I found the following entry in the log file:
> > Using user-mode PPS timestamp
> > Does it mean NTP reads the GPS strings and sees the 1PPS signal?
> > All the values are still 0 including reach. At one point for about 10
> > minutes, I saw some values after rebooting the machine but they
> > disappeared quickly.
> > Thanks.
> > jack
> > ps: I am using the latest NTP from Dave Hart's website. I also
> > installed serialpps.sys.
> Jack,
> As Dave Hart has answered you are talking to the expert in this area!
> I had assumed in my first response that you had a GPS receiver with a
> serial output connected to a serial-USB convertor, but I see now that this
> may not be the case.  How well the PPS output is emulated in the
> USB-serial port software you will need to check.  You need somehow to
> "connect" the PPS output from the GPS to the virtual DCD line of the
> emulated COM1 port.  Not quite sure how you do that.  What GPS and
> software are you using
> Cheers,
> David

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