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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: GPS time for celestial (longish)
From: Bob Hardin
Date: 1997 May 19, 09:40 EDT
From: Bob Hardin
Date: 1997 May 19, 09:40 EDT
I quote from: http://galaxy.einet.net/editors/john-beadles/sum_frq.htm You can see that a receiver can correct automatically or you can get the difference from the navigation message. "GPS Time Internally in the Navstar system, time is kept as GPS time. GPS Time began on January 6, 1980 and is referenced in GPS Weeks and seconds. GPS time is a composite time composed of the times of all available satellite and monitor station clocks. It is monitored by the GPS Operational Control System and by the U.S. Naval Observatory and is steered to keep it within 1 microsecond of UTC. However, leap seconds are not inserted so GPS time lags behind UTC. The exact difference is provided as constants in the GPS navigation message. By using the information given in the NAV message, the user can refer time via GPS directly to UTC (as determined by the USNO) with a precision of better than 340 nanoseconds (95% probability) using the standard positioning service and 100 nanoseconds using the precise positioning service." ... "Inexpensive Methods of GPS Time Syncronization Windows NT Resource Kit Want to syncronize the clock on your PC? I was looking through the Windows NT 3.51 Resource Kit the other day and what did I find but a time syncronization utility. On reading through the documentation, I found that it would accept output from a GPS receiver! The docs indicated that it would accept the output of Trimble and Rockwell receivers. Tom Clark's Totally Accurate Clock project Tom Clark from NASA's (?) has developed a high quality timing module from a low cost GPS receiver. The Totally Accurate Clock (TAC) project began as a home project, but was found to have applications in the scientific community as well. Incidentally, the name "Totally Accurate Clock" is a take-off on the old Heathkit "Most Accurate Clock" that syncronized itself to WWV signals. The TAC uses a Motorola Oncore Basic equipped with Option A (timing) and a small home built PC board containing additional buffering circuitry and signal amplification. ... Details and software for the TAC are <a href="ftp://aleph.gsfc.nasa.gov/GPS/totally.accurate.clock/">available by FTP</a>. People that have additional questions about the TAC can read the <a href="<A HREF="http://web.archive.org/web/20060512015644/ftp://aleph.gsfc.nasa.gov/GPS/totally.accurate.clock/tac.faq">ftp://aleph.gsfc.nasa.gov/GPS/totally.accurate.clock/tac.faq">FAQ</a>." ---------- Subject: Re: [Nml] GPS time for celestial I am writing this in the hope that someone can tell me what the >"watch error" is for the GPS time signal as received. ?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-?? ? TO UNSUBSCRIBE, send this message to majordomo@XXX.XXX: ? ? navigation ? ?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-?-??