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

Hal Murray hmurray at megapathdsl.net
Sat Jul 30 18:48:21 EDT 2016

holrum at hotmail.com said:
> 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. ...

Have you tried bigger bins?  10 microseconds was too small for me.  100 
worked well.

The SiRF chips are famous for horrible timing.  The arrival times were spread 
over 100 ms, but it was a slow wander rather than random jitter.  The pattern 
was a sawtooth, but the period was hours to many hours.  Something like that 
could lead to what you are seeing.

The old Garmin GPS-18 was reasonably good.  The new GPS-18x has the same 
horrible pattern as the SiRF.

These are my opinions.  I hate spam.

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