This morning I waited for the VLF timing signals to settle into their steady daytime phase - still showing the slow cycle of phase variation.
Then I power-cycled the GPS, leaving everything else running. During the 25 seconds it takes the GPS to begin sending PPS again, my software continues to time the VLF signal using the average PPS pulse interval measured over the previous 100 or so seconds. See the phase plot of DCF 77.5kHz for the result, http://abelian.org/vlf/live/pp100702dcfa.png GPS rebooted at 16686 seconds, just after the slow cycle started its upward ramp. It seems to have caused a phase jump in the slow cycle - it switched to starting a downward ramp. To confirm, I rebooted the GPS again at 24915 seconds, as it was about half way down a downward ramp. Again a step change of phase, this time it restarted at the bottom of an upward ramp. Just to eliminate any effect in my software, I unplugged the PPS signal from the soundcard for 30 seconds, leaving the GPS running. My software is starved of PPS for the same length of time as during the GPS reboots. This occurred at 27440 seconds, halfway along a downward ramp. The ramp continued down. Just to 'shake the bag' of temperature effects, I opened the door of the cabinet containing the PCs and electronics, this quickly dropped the temperature by 10 C. Also took out the unit containing the RC pulse forming, took its lid off and left it in the open air. Result: no noticeable change to the slow cycle. Well now, this sure looks to me like a GPS effect. I think I'd better order another GPS, a different type, maybe a GlobalSat MR-350P, or something, for comparison. Recommendations? Will also try to move the GPS16 so that it can see more of the sky - only about 50% visible at the moment, some trees block the other half. -- Paul Nicholson http://abelian.org -- _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
