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

jack j.jack.wang at gmail.com
Fri Nov 27 20:26:01 UTC 2009


David,

Would you mind looking up the model number of the Sitecom serial to
USB converter that has the DCD line? I am very interested in a
solution like that.

Jack

On Nov 27, 2:11 pm, "David J Taylor" <david-tay... at blueyonder.not-this-
bit.nor-this-part.co.uk.invalid> wrote:
> > Just to let everyone know that the u-blox GPS works well now. The
> > offset is 0.02ms with jitter at 0.002ms. My other GPS with only USB
> > out has an offset of 5ms and jitter of 2.5ms.
>
> > Jack
>
> Good news, Jack.  For comparison, my own tests with a serial to USB
> converter (Sitecom) which did include the DCD line (we think) I saw a
> minimum averaged jitter of about 45 microseconds, whereas with a LAN
> connection it had been 110-140 microseconds.  A direct serial port
> connection (yes, you /ca/n still get computers with them, but it's
> becoming more difficult) showed minimum averaged jitter in the order of
> 2 - 3 microseconds (with Windows XP).
>
> The kernel-mode PPS driver allowed a minimum averaged jitter of just over
> 3 microseconds to be reduced to a much steadier just over 2 microseconds,
> but had almost no effect on the offset or frequency variation.
>
> With Windows-7 and a direct serial GPS/PPS connection, the offset is far
> less, but the minimum averaged jitter is around 25 microseconds (PC
> Stamsund).
>
> It looks like that you need a direct serial connection if you want the PCs
> to be synced to within the millisecond.  Perhaps much better to have
> completely separate time stamp to which both PCs refer.
>
> Cheers,
> David




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