[1]ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.pdfHal Murray said:
> Noise like the oncore sawtooth isn't always a bad thing. I was going to comment on that area... Thanks for the reminder. The problem is that the sawtooth isn't noise in the normal Gaussian sense. If you happen to hit a long/wide hanging bridge, the resulting offset may get past your PLL filter. It might be possible to avoid hanging bridges by dithering the sawtooth. I'm thinking of something like a heater under the xtal for the GPS unit that gets driven by a medium frequency - slow relative to the normal sawtooth but fast relative to the PLL time constant. This somehow feels not-good, but I can't see the obvious screwup. Lots of experience shows that the hanging bridges are a killer. I have tried very hard to come up with PLL algorithms so that they don't kill performance. Unfortunately, the characteristic time between them falls right at the loop time constants you want to use to correct typical oscillators. Rick Hambly and I gave a paper at the PTTI meeting 2 weeks ago on how to remove them in hardware -- see "Improving the Performance of Low Cost GPS Timing Receivers" at [2]ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.ppt or [3]ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.pdf (the PPT is a huge 33MB in size, the PDF is a much smaller at ~2.5MB). You might find some of the other papers archived on [4]http://gpstime.com to be useful. 73, Tom References 1. ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.pdf 2. ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.ppt 3. ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.pdf 4. http://gpstime.com/ _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
