Björn Gabrielsson wrote on 24-4-2008 22:44: > Hi Jan, > > On Thu, 2008-04-24 at 21:37 +0200, Jan Hoevers wrote: >> Kipton Moravec wrote on 24-4-2008 18:14: >>> 1. A GPS module with the ability to expand the serial port to more than >>> 10 to allow you to use the NTP NEMA driver. The time pulse would be >>> accurate to about 30 nS RMS. Retail cost about $100. >> Quite unlikely, since the GPS system itself does not have 30 ns >> accuracy. That kind of accuracy is meaningless for pool server >> operators anyhow. They typically do not own cesium clocks and the >> regular pc oscillator is not stable enough to maintain that kind of >> accuracy. > > I agree with your conclusion that 30ns is meaningless for NTP use. > > However why do you say the GPS system itself does not have 30ns > accuracy. > > The signal in space (SIS) accuracy quoted for the current constellation > is between 1 and 2 meters, which is well below 10ns.
Well, maybe you're right and my information is outdated. This page (http://tycho.usno.navy.mil/gpstt.html) speaks about "a few hundred nanoseconds". I recall 340 ns but I forgot where I read it. Anyhow, a 30 ns accuracy cannot be transferred over an ethernet, let alone the internet. It cannot be maintained without a cesium time base. This may be interesting for a well equipped lab, but not for us. Jan _______________________________________________ timekeepers mailing list [email protected] https://fortytwo.ch/mailman/cgi-bin/listinfo/timekeepers
