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Discussion of precise time and frequency measurement

Adafruit Ultimate GPS timing message arrival times

Mark Sims

Sun, Jul 31, 2016 4:03 PM

Are you sure that the arrival time is negative? In my experience, the NMEA message is /after/ the PPS, and not before it.

As mentioned in the post the times reported are the time stamp in the receiver packet minus the system clock time when it was received... negative value indicate the message arrives after the PPS. The polarity of the reported value is consistent with how Lady Heather makes use of the value... --------------- > Are you sure that the arrival time is negative? In my experience, the NMEA message is /after/ the PPS, and not before it.

David J Taylor

Mon, Aug 1, 2016 6:24 AM

From: Mark Sims

As mentioned in the post the times reported are the time stamp in the
receiver packet minus the system clock time when it was received...
negative value indicate the message arrives after the PPS. The polarity of
the reported value is consistent with how Lady Heather makes use of the
value...

Thanks, Mark. I'd missed that in the post. I still find it confusing to
plot positive times as negative ones.

From your data and my own measurements, I feel that using the serial NMEA

stream would, today, be a last resort, as an Internet sync would be
considerably better. Would you agree with that?

Cheers,
David

SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv

From: Mark Sims As mentioned in the post the times reported are the time stamp in the receiver packet minus the system clock time when it was received... negative value indicate the message arrives after the PPS. The polarity of the reported value is consistent with how Lady Heather makes use of the value... =========================== Thanks, Mark. I'd missed that in the post. I still find it confusing to plot positive times as negative ones. >From your data and my own measurements, I feel that using the serial NMEA stream would, today, be a last resort, as an Internet sync would be considerably better. Would you agree with that? Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-taylor@blueyonder.co.uk Twitter: @gm8arv