[time-nuts] Ublox Neo-6M time error.

Mark Sims holrum at hotmail.com
Tue May 31 21:20:27 EDT 2016


I had two machines running Lady Heather with the singing chime clock mode enabled (that plays a chant from the Missa Assumpta on the quarter hours).   

One machine was connected to a Ublox Neo-6M receiver and another to a Z3801A.   I noticed that the two machines sang their jaunty monk tunes offset by around one second.  Since a man with two singing GPS clocks never knows what time it is,  I replaced the Z3801A with a Jupiter-T and the two clocks were still out of sync.   Finally I tried  Motorola M12+ and UT receivers and the same thing happened.  It looks like the Ublox time is ahead by a second compared to all the other receivers.   I then specified a -1 second "rollover" correction to the Ublox machine and the two clocks sang in perfect harmony.   Has anybody noticed such behavior with other receivers?

BTW,  note that the Ublox binary time message has a "fractional nanoseconds of the seconds field" (+/- 500,000 nanoseconds) correction that must be applied to the hrs:min:secs values (which I am doing).  The fractional time offset forms a sawtooth with around a 120 second period.  Attached is a GIF... white is the nanosecond fractional time offset.  Magenta is the receiver estimate of its time error (both in nanoseconds).  The Trimble Resolution-T receivers report a similar "local clock bias" value, but they don't seem to document what it actually is...



 		 	   		  
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