> Tom, > > Good points. I think that a lot of people are unaware of the diurnal > shifts that occur due to atmospherics. These can be many 10's of > noseconds compared to UTC. This is true for every receiver I have ever > worked with. The ionospheric correction algorithms are good, but they > are not perfect. Can't wait for a civilian L2..................... > > > Randy
Right. What gets in the way of accurate UTC time from an M12+, or just about any other GPS receiver is: (not in any particular order): -- antenna cable feed delays -- antenna delays -- antenna phase center errors -- internal receiver hardware delays -- external receiver connector or other cabling delays -- trigger level or zero-crossing errors -- antenna preamp, RF filter, or splitter delays -- humidity -- tempco in all of the above -- voltco in some of the above -- receiver firmware delays -- sawtooth errors -- 1PPS quantization errors -- imprecise zero-D position measurement -- PPF (pigeon poop factor ;-) -- multi-path errors (large) -- GPS SV clock errors -- GPS SV ephemeris errors -- ionospheric errors (large) -- tropospheric errors (small) -- UTC(USNO) errors Some of these vary with ~12 or ~24 hour periods; some of these vary with 1 year periods; some of these show sudden jumps; some of these show gradual drift; some of these just wander around over time. You get the idea. Some are ps, ps/K, some are ns, some are tens of ns. I wish I could give you a nice list with hard numbers but I don't know. Perhaps Tom Clark does? I also don't have any data to back up this bold claim, but: I would be surprised if any of us, me included, has UTC at home closer than maybe 20 to 50 ns. -- with the exception of DougHo (with his USNO calibrated, real-time JPL corrected, frequency-steered, 5071A-driven, post-processed, dual frequency Z12T) and the one or two of you on the list that work at TSC. What most of us time-nuts use GPS receivers for is quartz, rubidium, or eBay-cesium *frequency* measurements, and so all these fixed, or slowly varying *time* offsets, have little or no effect on our measurements. /tvb http://www.LeapSecond.com _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
