Hal Murray wrote: >> 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. > > Hal
Avoidance of hanging bridges requires that the GPS receiver oscillator frequency not be a Hamonic of 1Hz at any time. Using a heater as you suggest will not solve this problem. Ideally it would be best if it were not a rational multiple of 1Hz either. Its generally simpler and easier to use the PPS sawtooth correction, if available. Resultant residual jitter is closer to Gaussian. Bruce _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
