[OZAPRS] Re: [amsat-bb] Online atomic clock

[Gavin Rogers]

At 07:14 AM 14/09/2005, you wrote:
>Norm .. There must be several ways to set the PC from a GPS clock .. Here
is
>one I know of.. The MoonBounce and WSJT boys as well as satellite
tracking
>fraternity all must do this in some way.. Look here
>http://nlsa.com/novagps.html
>There are probably feebies that do it as well..

The standard 'ntpd' reference implementation of NTP supports GPS 
input very well. With a simple circuit to stretch the 1 pulse per 
second pulse out a few more milliseconds so the serial UART can catch 
it, I get an accurate clock on my Linux box with the PPS patches.

ntpq -p
      remote           refid      st t when poll reach   delay   offset
jitter
==========================================================================
====
+GENERIC(0)      GENERIC(0)       1 l   40   64  377    0.000  -11.986
6.202
oPPS(0)          GENERIC(0)       1 l   33   64  377    0.000    0.003
0.003

Without using the PPS patch and if your GPS only supports NMEA output 
(i.e. no PPS output) then the best accuracy you're going to get is 
around the 1-200ms range. For that, it's not worth the effort and 
you'd might as well sync using ntpd etc to your ISPs time server.

If anyone wants further info, I'd be happy to help.


73
Gavin.

---
       Gavin Rogers                     |  Amateur radio station VK6HGR
     http://www.livingwaters.com/good   |     http://vk6hgr.ampr.org/
    ICQ: 17230395  MSN: VK6HGR  Skype/Email: grogers at vk6hgr.echidna.id.au

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