[ntp:questions] UTC Time from NMEA receiver one second behind DCF?

David J Taylor david-taylor at blueyonder.neither-this-bit.nor-this-bit.co.uk
Wed Aug 13 06:25:35 UTC 2008

Harald Brinkmann wrote:
> But even problems caused by a slow data transmission wouldn't explain
> why the observed offset is small compared to one second most of the
> time (and in my case continuously for well over a year) and suddenly
> and only on certain days there is an offset of almost exactly one
> second, unless the messages are suddenly and only on those days
> extraordinarily long and just happen to delay everything by one
> second. I'll have a lookout for the raw NMEA messages the next time
> this happens. *If* I were using a PPS signal, I could understand the
> system being confused about which NMEA message belongs to which PPS
> pulse, so one would get an offset of (maybe multiples of) one second.
> But that's not the case here.
> Harald

No, indeed.  Hal's graph shows it nicely.  I have a SiRF III chip set 
equipped GPS (Garmin GPS60 CSx), but it doesn't display the seconds (or is 
there a screen where it does?).  One casual check suggested that it 
changed from 06:20 to 06:21 UTC at about the expected instant, using the 
clock on the map display screen, but I've done no systematic checks.

I do hope you get to the bottom of this.


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