[time-nuts] Adafruit Ultimate GPS timing message arrival times

David J Taylor david-taylor at blueyonder.co.uk
Sun Jul 31 03:15:54 EDT 2016

From: Mark Sims

A couple of people have asked about the poor message arrival time 
performance of the popular Adafruit Ultimate GPS receiver.   I modified Lady 
Heather to analyze the message arrival times using a histogram instead of a 
simple average.  When I looked at the histogram data (.01 msec resolution), 
I was rather shocked...  With an hour of data,  most receivers have maybe a 
couple dozen bins hit,  with the peak bin several hundred counts above the 
next lower peak.   The Adafruit had over 1800 bins hit, with the peak bin 
having six hits.   Attached is the histogram...  you probably don't want to 
use this receiver to drive a clock based upon message arrival times...


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

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Email: david-taylor at blueyonder.co.uk
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