Hi: I've been comparing s/n 1227 aginst GPS for a couple of weeks and am within a tick or two of getting the c field optimized. I think the current actual offset is less than +2.2E-13, but R^2 is only at 0.2 so am not really sure yet.
A problem that shows up every now and then is that the standard deviation on a 500 second average is above 10 ns (typical is 9 ns). For example here is some data all this morning (17 May 06): Time Interval (ps) time sigma 975803 04:49:20 9 969817 04:57:40 98 919359 05:06:00 240 838596 05:14:20 349 957634 05:22:40 150 979542 05:31:00 9 917433 05:39:20 244 903613 05:47:40 267 913995 05:56:00 251 936876 06:04:20 206 976696 06:12:40 9 973410 06:21:00 62 959098 06:29:20 144 976590 06:37:40 9 I have a couple of ideas of what might be causing this. One is that there were no satellites to track and the crystal in the M12+T drifted, but think this is almost impossible since the elevation mask now is at 20 degrees. The other is multipath. Is there any information on how multipath effects the M12+T? I would think that in 0-D mode and tracking only one satellite then multipath would be a factor, but if tracking a bunch of satellites then multipath on one of them would not be a factor. Since I'm logging the sigma when I see this I just toss the data. Notice that for the 3 points where sigma is 9 ns the TI looks like: 975803 979542 976696 976590 Where the spread is under 5 ns which is good. I would like to know what's causing this. Any thoughts? Have Fun, Brooke Clarke -- w/Java http://www.PRC68.com w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
