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

Bob Stewart bob at evoria.net
Sat Jul 30 17:59:04 EDT 2016

I liked the Adafruit too when I was using it a couple of years ago, but it did have a bad habit of going walkabout.  Yeah, a lot of that was my antenna, but it's still worth mentioning.
Bob -----------------------------------------------------------------


      From: Tom Van Baak <tvb at LeapSecond.com>
 To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
 Sent: Saturday, July 30, 2016 4:32 PM
 Subject: Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times
Hi Brooke,

That's a reasonable assumption. I haven't ever tried mine at 10 Hz. But note that fast update rates is more meant for navigation and positioning than it is for timing.

Just in case we have some newcomers to the thread I'd like to point out that this recent series of measurements of RS232 / NMEA have no bearing at all on the quality of the timing output. Timing NMEA is more of a curiosity; something to measure at the hundreds or tens of millisecond level. As anyone knows, the real timing output of these receiver is the 1PPS pulse itself, which is good to the tens of nanoseconds level. So a factor of a million different.

I actually like the Adafruit GPS receiver, and would recommend it to anyone. I use it for projects around the house more than any other receiver. It's so simple to use -- no configuration needed, no sawtooth correction needed, no survey required, fast acquisition, works fixed or mobile, sensitive antenna included on board, small and low power, just give it 5 volts and out comes a UTC 1PPS.

Its 1PPS output is superb. Attached is the ADEV/MDEV of the raw 1PPS of the Adafruit GPS board.


----- Original Message ----- 
From: "Brooke Clarke" <brooke at pacific.net>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Saturday, July 30, 2016 1:50 PM
Subject: Re: [time-nuts] Adafruit Ultimate GPS timing message arrival times

> Hi Mark:
> Isn't this the receiver that hears a very large number of GNSS satellites and also has a 10 Hz update rate?
> If so, I'd expect that there would a large variation in message lengths.  How stable  is the 10 PPS or 1 PPS output?
> -- 
> Have Fun,
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
> The lesser of evils is still evil.
> -------- Original Message --------
>> 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...
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