Dan Drown <dan-...@drown.org>: > >We may already be at a technological place where GPS outages don't bust the > >tolerable-error budget, even with cheap hardware. If we aren't, we'll > >probably be there soon. One of my medium-term agenda items is to measure > >and see. > > I had setup a test along these lines a week ago: > https://blog.dan.drown.org/gps-pps-drift-when-it-has-no-signal/ > > The GPS module I'm using still outputs PPS even when it loses lock. > That won't be true for every GPS module. > > My results were a long term average of 250us-500us lost per day > (~3-6ppb). This surprised me because of how low it was, I assume I > got lucky with the long term average temperature of the GPS module. > > ntpsec finally rejected the PPS at a 2ms offset. I think I could > change that with the "tos mindist" setting (which was at its default > of 1ms), but I haven't verified that. > > Of course, this data doesn't apply to all GPS outage situations. But > it does suggest that holdover within 30ms is easy for the "can't hear > the satellites for a few hours" case.
Very interesting. I have a USB thermometer on order, they're cheap. Might I suggest you get one and repeat this experiment, actually plotting your temperature variation? -- <a href="http://www.catb.org/~esr/">Eric S. Raymond</a> _______________________________________________ devel mailing list devel@ntpsec.org http://lists.ntpsec.org/mailman/listinfo/devel