MS

Mark Sims

Sat, Jul 30, 2016 8:14 PM

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...

BC

Brooke Clarke

Sat, Jul 30, 2016 8:50 PM

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...

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

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... > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

TV

Tom Van Baak

Sat, Jul 30, 2016 9:32 PM

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.

/tvb

----- Original Message -----
From: "Brooke Clarke" brooke@pacific.net
To: "Discussion of precise time and frequency measurement" time-nuts@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...

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. /tvb ----- Original Message ----- From: "Brooke Clarke" <brooke@pacific.net> To: "Discussion of precise time and frequency measurement" <time-nuts@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... >>

BS

Bob Stewart

Sat, Jul 30, 2016 9:59 PM

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 -----------------------------------------------------------------
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Tom Van Baak <tvb@LeapSecond.com>

To: Discussion of precise time and frequency measurement time-nuts@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.

/tvb

----- Original Message -----
From: "Brooke Clarke" brooke@pacific.net
To: "Discussion of precise time and frequency measurement" time-nuts@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...

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

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 ----------------------------------------------------------------- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Tom Van Baak <tvb@LeapSecond.com> To: Discussion of precise time and frequency measurement <time-nuts@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. /tvb ----- Original Message ----- From: "Brooke Clarke" <brooke@pacific.net> To: "Discussion of precise time and frequency measurement" <time-nuts@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... >> _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

NS

Nick Sayer

Sat, Jul 30, 2016 11:12 PM

I’ve used the PA6H so far for all of my GPSDOs. The two reasons I am considering the Venus838LPx-T to replace it are that it has a sawtooth correction message and it has a survey and static solution mode to allow it to tolerate poorer reception.

I’m driven to want to experiment with a static mode GPS receiver from this page on Atilla Kinali’s blog: https://attila.kinali.ch/blog/2016/02/07/gps-disciplined-oscillator, which references some e-mail here from some time ago. My take-away was that navigation mode receivers could achieve good results as long as they had ideal reception, but with poor reception they would do much worse than a receiver in static mode that’s done a good survey.

As for the sawtooth correction, I’m less convinced that it’s required given that I’m using averaging on the phase detector output. I can’t detect hanging bridges with the current setup, but since I haven’t actually looked for them, ignorance is bliss. Tom, if you still have the data, can you speak to whether you saw anything of the sort? In any event, it’s a box I’d like to check if for no other reason than to learn something.

On Jul 30, 2016, at 2:32 PM, Tom Van Baak tvb@LeapSecond.com wrote:

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.

/tvb

----- Original Message -----
From: "Brooke Clarke" brooke@pacific.net
To: "Discussion of precise time and frequency measurement" time-nuts@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...

<gps-mtk3339-adev-mdev.gif>_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

I’ve used the PA6H so far for all of my GPSDOs. The two reasons I am considering the Venus838LPx-T to replace it are that it has a sawtooth correction message and it has a survey and static solution mode to allow it to tolerate poorer reception. I’m driven to want to experiment with a static mode GPS receiver from this page on Atilla Kinali’s blog: https://attila.kinali.ch/blog/2016/02/07/gps-disciplined-oscillator, which references some e-mail here from some time ago. My take-away was that navigation mode receivers could achieve good results as long as they had ideal reception, but with poor reception they would do much worse than a receiver in static mode that’s done a good survey. As for the sawtooth correction, I’m less convinced that it’s required given that I’m using averaging on the phase detector output. I can’t detect hanging bridges with the current setup, but since I haven’t actually looked for them, ignorance is bliss. Tom, if you still have the data, can you speak to whether you saw anything of the sort? In any event, it’s a box I’d like to check if for no other reason than to learn something. > On Jul 30, 2016, at 2:32 PM, Tom Van Baak <tvb@LeapSecond.com> wrote: > > 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. > > /tvb > > ----- Original Message ----- > From: "Brooke Clarke" <brooke@pacific.net> > To: "Discussion of precise time and frequency measurement" <time-nuts@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... >>> > <gps-mtk3339-adev-mdev.gif>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.

DJ

David J Taylor

Sun, Jul 31, 2016 7:15 AM

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...

Mark,

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

Cheers,
David

SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv

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... ============================== Mark, Are you sure that the arrival time is negative? In my experience, the NMEA message is /after/ the PPS, and not before it. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-taylor@blueyonder.co.uk Twitter: @gm8arv

GE

Gary E. Miller

Mon, Aug 1, 2016 6:51 PM

Yo Mark!

On Sat, 30 Jul 2016 20:14:02 +0000
Mark Sims holrum@hotmail.com wrote:

A couple of people have asked about the poor message arrival time
performance of the popular Adafruit Ultimate GPS receiver.

I have several months of Adafruit graphs. I also find that is is usually
as accurate as you would expect. But often it just seems to have
huge swings in Lat/Lon even while stationary.

Here is are two 24 hour scatter plots:

https://pi2.rellim.com/pi2.png
https://pi2.rellim.com/pi2-2.png

RGDS
GARY

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com Tel:+1 541 382 8588

Yo Mark! On Sat, 30 Jul 2016 20:14:02 +0000 Mark Sims <holrum@hotmail.com> wrote: > A couple of people have asked about the poor message arrival time > performance of the popular Adafruit Ultimate GPS receiver. I have several months of Adafruit graphs. I also find that is is usually as accurate as you would expect. But often it just seems to have huge swings in Lat/Lon even while stationary. Here is are two 24 hour scatter plots: https://pi2.rellim.com/pi2.png https://pi2.rellim.com/pi2-2.png RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 gem@rellim.com Tel:+1 541 382 8588

time-nuts@lists.febo.com

Adafruit Ultimate GPS timing message arrival times

Cheers, David

RGDS GARY

Cheers,
David

RGDS
GARY