Hit "send" a bit to soon. NTP will use the "best" reference clocks it finds. If that is GPS it will use that. It can also use other NTP servers. Typically people use those rather then getting their own GPS receiver. If the PC has a network connection you can likely get time to within a few milliseconds using NTP and a few of the pool time servers.
I would defiantly recommend getting NTP to work using the pool servers first. Then add GPS. Be warned that the NMEA spec says that messages apply to the current second. This means the NMEA data from the serial port can be up to one second "off". It is used only to tell you the number of the second, not for accurate timing. For that NTP uses the PPS reference clock. On some GPS receivers (not your Garmin unit) the PPS is good for a few tens of nanoseconds. I looked up NMEATime. It uses "SNTP" protocol. It will never be very accurate. Think about a mechanical clock that you want to set. First to set it then you wait a day or so and see if it gains or looses time. Then you adust the rate, faster or slower. Eventually the clock keeps good time after a few more cycles of adjust and wait and check. NTP works like this. SNTP simply sets the clock once then quits and never even looks at the rate. This is the place to get NTP http://www.ntp.org However many Windows users like to get third party versions of NTP. These are packages with installers and are good for people who can't build and install the source distribution. Google should find one. About your Garmin GPS. You can buy a real "timing receiver" for under $20 on eBay. If you need nanoseconds that is the way to go. A timing reciever will have at least two features (1) position hold, where the receiver is told it is NOT moving and (2) self survey, where the reciever can take about 30 minutes or longer to deterim it's position to typically less than a meter. Position uncertainty creates time uncertainty (by the speed of light) so not knowing you location by a meter means you don't know the time within about 3 nanoseconds. On Wed, Aug 21, 2013 at 11:48 PM, Chris Albertson <albertson.ch...@gmail.com > wrote: > It's simple, just install and run "NTP" > http://www.ntp.org/downloads.html > > > On Wed, Aug 21, 2013 at 9:02 PM, Rex Moncur <rmon...@bigpond.net.au>wrote: > >> I am trying to lock a Windows XP computer to GPS time taking advantage of >> both the NEMA sentence and the 1PPS with the hope of getting to within a >> few >> ms. >> >> I am using a Garmin GPS 18PC and the NMEATime program. When I tick the >> box >> to implement the 1PPS feature on NMEATime the program locks up each time >> it >> attempts to correct the PC time. Perhaps there is something I need to do >> to >> configure the GPS 18PC to fix this. >> >> I would be grateful for advice as to whether and how one can use NMEATime >> for this purpose with a Garmin GPS 18 PC or advice on other programs to >> achieve accurate locking of the PC. >> >> Rex VK7MO >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > -- > > Chris Albertson > Redondo Beach, California > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.