Empathy List Archives

HT

Håkan T Johansson

Sat, Feb 11, 2023 10:09 AM

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a
MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20
ns jitter, with long-term wanders of 100 ns, presumably due to my limited
sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

Hi, I have a NTP server project based on a Digilent Arty A7 FPGA board with a MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns jitter, with long-term wanders of 100 ns, presumably due to my limited sky-view. More details: http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html Cheers, Håkan

BK

Bob kb8tq

Sat, Feb 11, 2023 10:38 PM

Hi

If you want to get the short term jitter down to around a second or so,
set it up with a GPS module that puts out a sawtooth correction. You
also need to get the Arty A7 measuring at the 1 ns level. That’s do-able
without insane amounts of effort.

Bob

On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts time-nuts@lists.febo.com wrote:

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns jitter, with long-term wanders of 100 ns, presumably due to my limited sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi If you want to get the short term jitter down to around a second or so, set it up with a GPS module that puts out a sawtooth correction. You also need to get the Arty A7 measuring at the 1 ns level. That’s do-able without insane amounts of effort. Bob > On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts <time-nuts@lists.febo.com> wrote: > > > Hi, > > I have a NTP server project based on a Digilent Arty A7 FPGA board with a MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns jitter, with long-term wanders of 100 ns, presumably due to my limited sky-view. More details: > > http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html > > Cheers, > Håkan > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

EM

Ed Marciniak

Sun, Feb 12, 2023 12:00 AM

Your mediatek GPS receiver is probably a really lousy pick for low jitter.

There are options from Navspark like the NS-T, other receiving chips/modules from the same, as well as some uBlox parts that would do better.

There’s options with under 20ns jitter on those, and if memory serves there’s one that’s available that with a good sky view and antenna might be more like 8ns jitter.

Get Outlook for iOShttps://aka.ms/o0ukef

From: Bob kb8tq via time-nuts time-nuts@lists.febo.com
Sent: Saturday, February 11, 2023 4:38:23 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Håkan T Johansson f96hajo@chalmers.se; Bob kb8tq kb8tq@n1k.org
Subject: [time-nuts] Re: FPGA-based GPS NTP server project

Hi

If you want to get the short term jitter down to around a second or so,
set it up with a GPS module that puts out a sawtooth correction. You
also need to get the Arty A7 measuring at the 1 ns level. That’s do-able
without insane amounts of effort.

Bob

On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts time-nuts@lists.febo.com wrote:

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns jitter, with long-term wanders of 100 ns, presumably due to my limited sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Your mediatek GPS receiver is probably a really lousy pick for low jitter. There are options from Navspark like the NS-T, other receiving chips/modules from the same, as well as some uBlox parts that would do better. There’s options with under 20ns jitter on those, and if memory serves there’s one that’s available that with a good sky view and antenna might be more like 8ns jitter. Get Outlook for iOS<https://aka.ms/o0ukef> ________________________________ From: Bob kb8tq via time-nuts <time-nuts@lists.febo.com> Sent: Saturday, February 11, 2023 4:38:23 PM To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Cc: Håkan T Johansson <f96hajo@chalmers.se>; Bob kb8tq <kb8tq@n1k.org> Subject: [time-nuts] Re: FPGA-based GPS NTP server project Hi If you want to get the short term jitter down to around a second or so, set it up with a GPS module that puts out a sawtooth correction. You also need to get the Arty A7 measuring at the 1 ns level. That’s do-able without insane amounts of effort. Bob > On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts <time-nuts@lists.febo.com> wrote: > > > Hi, > > I have a NTP server project based on a Digilent Arty A7 FPGA board with a MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns jitter, with long-term wanders of 100 ns, presumably due to my limited sky-view. More details: > > http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html > > Cheers, > Håkan > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com

HT

Håkan T Johansson

Sun, Feb 12, 2023 11:51 AM

Hi,

perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board?
That looks like 8 ns jitter, and the UBX-TIM-TP message should give the
sawtooth.

A 0.5 ns sampler I actually have on the FPGA.

Cheers,
Håkan

On Sun, 12 Feb 2023, Ed Marciniak wrote:

Your mediatek GPS receiver is probably a really lousy pick for low jitter.

There are options from Navspark like the NS-T, other receiving chips/modules
from the same, as well as some uBlox parts that would do better.

There’s options with under 20ns jitter on those, and if memory serves
there’s one that’s available that with a good sky view and antenna might be
more like 8ns jitter.

Get Outlook for iOS

From: Bob kb8tq via time-nuts time-nuts@lists.febo.com
Sent: Saturday, February 11, 2023 4:38:23 PM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Håkan T Johansson f96hajo@chalmers.se; Bob kb8tq kb8tq@n1k.org
Subject: [time-nuts] Re: FPGA-based GPS NTP server project
Hi

If you want to get the short term jitter down to around a second or so,
set it up with a GPS module that puts out a sawtooth correction. You
also need to get the Arty A7 measuring at the 1 ns level. That’s do-able
without insane amounts of effort.

Bob

On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts
time-nuts@lists.febo.com wrote:

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a
MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns
jitter, with long-term wanders of 100 ns, presumably due to my limited
sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi, perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board? That looks like 8 ns jitter, and the UBX-TIM-TP message should give the sawtooth. A 0.5 ns sampler I actually have on the FPGA. Cheers, Håkan On Sun, 12 Feb 2023, Ed Marciniak wrote: > Your mediatek GPS receiver is probably a really lousy pick for low jitter. > > There are options from Navspark like the NS-T, other receiving chips/modules > from the same, as well as some uBlox parts that would do better. > > There’s options with under 20ns jitter on those, and if memory serves > there’s one that’s available that with a good sky view and antenna might be > more like 8ns jitter. > > Get Outlook for iOS > > ____________________________________________________________________________ > From: Bob kb8tq via time-nuts <time-nuts@lists.febo.com> > Sent: Saturday, February 11, 2023 4:38:23 PM > To: Discussion of precise time and frequency measurement > <time-nuts@lists.febo.com> > Cc: Håkan T Johansson <f96hajo@chalmers.se>; Bob kb8tq <kb8tq@n1k.org> > Subject: [time-nuts] Re: FPGA-based GPS NTP server project > Hi > > If you want to get the short term jitter down to around a second or so, > set it up with a GPS module that puts out a sawtooth correction. You > also need to get the Arty A7 measuring at the 1 ns level. That’s do-able > without insane amounts of effort. > > Bob > > > On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts > <time-nuts@lists.febo.com> wrote: > > > > > > Hi, > > > > I have a NTP server project based on a Digilent Arty A7 FPGA board with a > MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns > jitter, with long-term wanders of 100 ns, presumably due to my limited > sky-view. More details: > > > > http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html > > > > Cheers, > > Håkan > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com > >

FC

Forrest Christian (List Account)

Sun, Feb 12, 2023 1:03 PM

Having shipped a lot of timing products with the mediatek chipsets, I can
confirm that the jitter described is expected, even with a perfect sky
view. This is acceptable in the application I'm using them in, may or
may not be acceptable to you.

On Sat, Feb 11, 2023, 7:58 AM Håkan T Johansson via time-nuts <
time-nuts@lists.febo.com> wrote:

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a
MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20
ns jitter, with long-term wanders of 100 ns, presumably due to my limited
sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Having shipped a lot of timing products with the mediatek chipsets, I can confirm that the jitter described is expected, even with a perfect sky view. This is acceptable in the application I'm using them in, may or may not be acceptable to you. On Sat, Feb 11, 2023, 7:58 AM Håkan T Johansson via time-nuts < time-nuts@lists.febo.com> wrote: > > Hi, > > I have a NTP server project based on a Digilent Arty A7 FPGA board with a > MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 > ns jitter, with long-term wanders of 100 ns, presumably due to my limited > sky-view. More details: > > http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html > > Cheers, > Håkan > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com >

BC

Bob Camp

Sun, Feb 12, 2023 10:40 PM

Hi

You don’t have to spend what the F9T’s cost simply to knock down the jitter. There are a
number of uBlox modules that have sawtooth correction data and cost < $40 mounted on
on a board.

Bob

On Feb 12, 2023, at 6:51 AM, Håkan T Johansson f96hajo@chalmers.se wrote:

Hi,

perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board?
That looks like 8 ns jitter, and the UBX-TIM-TP message should give the sawtooth.

A 0.5 ns sampler I actually have on the FPGA.

Cheers,
Håkan

On Sun, 12 Feb 2023, Ed Marciniak wrote:

Your mediatek GPS receiver is probably a really lousy pick for low jitter.
There are options from Navspark like the NS-T, other receiving chips/modules
from the same, as well as some uBlox parts that would do better.
There’s options with under 20ns jitter on those, and if memory serves
there’s one that’s available that with a good sky view and antenna might be
more like 8ns jitter.
Get Outlook for iOS

From: Bob kb8tq via time-nuts time-nuts@lists.febo.com
Sent: Saturday, February 11, 2023 4:38:23 PM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Håkan T Johansson f96hajo@chalmers.se; Bob kb8tq kb8tq@n1k.org
Subject: [time-nuts] Re: FPGA-based GPS NTP server project
Hi
If you want to get the short term jitter down to around a second or so,
set it up with a GPS module that puts out a sawtooth correction. You
also need to get the Arty A7 measuring at the 1 ns level. That’s do-able
without insane amounts of effort.
Bob

On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts

time-nuts@lists.febo.com wrote:

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a

MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns
jitter, with long-term wanders of 100 ns, presumably due to my limited
sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi You don’t have to spend what the F9T’s cost simply to knock down the jitter. There are a number of uBlox modules that have sawtooth correction data and cost < $40 mounted on on a board. Bob > On Feb 12, 2023, at 6:51 AM, Håkan T Johansson <f96hajo@chalmers.se> wrote: > > > Hi, > > perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board? > That looks like 8 ns jitter, and the UBX-TIM-TP message should give the sawtooth. > > A 0.5 ns sampler I actually have on the FPGA. > > Cheers, > Håkan > > > On Sun, 12 Feb 2023, Ed Marciniak wrote: > >> Your mediatek GPS receiver is probably a really lousy pick for low jitter. >> There are options from Navspark like the NS-T, other receiving chips/modules >> from the same, as well as some uBlox parts that would do better. >> There’s options with under 20ns jitter on those, and if memory serves >> there’s one that’s available that with a good sky view and antenna might be >> more like 8ns jitter. >> Get Outlook for iOS >> ____________________________________________________________________________ >> From: Bob kb8tq via time-nuts <time-nuts@lists.febo.com> >> Sent: Saturday, February 11, 2023 4:38:23 PM >> To: Discussion of precise time and frequency measurement >> <time-nuts@lists.febo.com> >> Cc: Håkan T Johansson <f96hajo@chalmers.se>; Bob kb8tq <kb8tq@n1k.org> >> Subject: [time-nuts] Re: FPGA-based GPS NTP server project >> Hi >> If you want to get the short term jitter down to around a second or so, >> set it up with a GPS module that puts out a sawtooth correction. You >> also need to get the Arty A7 measuring at the 1 ns level. That’s do-able >> without insane amounts of effort. >> Bob >> > On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts >> <time-nuts@lists.febo.com> wrote: >> > >> > >> > Hi, >> > >> > I have a NTP server project based on a Digilent Arty A7 FPGA board with a >> MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns >> jitter, with long-term wanders of 100 ns, presumably due to my limited >> sky-view. More details: >> > >> > http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html >> > >> > Cheers, >> > Håkan >> > _______________________________________________ >> > time-nuts mailing list -- time-nuts@lists.febo.com >> > To unsubscribe send an email to time-nuts-leave@lists.febo.com >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com

HT

Håkan T Johansson

Mon, Mar 6, 2023 7:25 AM

Hi,

thanks for all the tips! With some NEO-7M and NEO-6M boards together with
a 0.5 ns sampling of the PPS and sawtooth correction message it is now
able to reach a jitter of about 2 ns of the PPS vs. the tracking.

Another thing came up:

For monitoring, I have found it quite useful to have an estimate of the
current tracking resolution in the NTP responses. However, the root
dispersion field does not have resolution enough (smallest non-0 value is
15.3 us) and thus only give useful reports when tracking is way off, e.g.
during initial lock. So I am (ab)using the precision field to report
log_2 of a running average of the absolute differences between the actual
and expected NTP timestamps at the PPS signals. With the previous 8 ns
sampling without sawtooth correction it reached around -26 to -27, and now
instead between -29 and -30.

Are there adverse effects of having a dynamically varying NTP precision
field?

Cheers,
Håkan

On Sun, 12 Feb 2023, Bob Camp wrote:

Hi

You don’t have to spend what the F9T’s cost simply to knock down the jitter. There are a
number of uBlox modules that have sawtooth correction data and cost < $40 mounted on
on a board.

Bob

On Feb 12, 2023, at 6:51 AM, Håkan T Johansson f96hajo@chalmers.se wrote:

Hi,

perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board?
That looks like 8 ns jitter, and the UBX-TIM-TP message should give the sawtooth.

A 0.5 ns sampler I actually have on the FPGA.

Cheers,
Håkan

On Sun, 12 Feb 2023, Ed Marciniak wrote:

Your mediatek GPS receiver is probably a really lousy pick for low jitter.
There are options from Navspark like the NS-T, other receiving chips/modules
from the same, as well as some uBlox parts that would do better.
There’s options with under 20ns jitter on those, and if memory serves
there’s one that’s available that with a good sky view and antenna might be
more like 8ns jitter.
Get Outlook for iOS

From: Bob kb8tq via time-nuts time-nuts@lists.febo.com
Sent: Saturday, February 11, 2023 4:38:23 PM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Håkan T Johansson f96hajo@chalmers.se; Bob kb8tq kb8tq@n1k.org
Subject: [time-nuts] Re: FPGA-based GPS NTP server project
Hi
If you want to get the short term jitter down to around a second or so,
set it up with a GPS module that puts out a sawtooth correction. You
also need to get the Arty A7 measuring at the 1 ns level. That’s do-able
without insane amounts of effort.
Bob

On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts
time-nuts@lists.febo.com wrote:

Hi,

I have a NTP server project based on a Digilent Arty A7 FPGA board with a
MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns
jitter, with long-term wanders of 100 ns, presumably due to my limited
sky-view. More details:

http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html

Cheers,
Håkan

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

Hi, thanks for all the tips! With some NEO-7M and NEO-6M boards together with a 0.5 ns sampling of the PPS and sawtooth correction message it is now able to reach a jitter of about 2 ns of the PPS vs. the tracking. Another thing came up: For monitoring, I have found it quite useful to have an estimate of the current tracking resolution in the NTP responses. However, the root dispersion field does not have resolution enough (smallest non-0 value is 15.3 us) and thus only give useful reports when tracking is way off, e.g. during initial lock. So I am (ab)using the precision field to report log_2 of a running average of the absolute differences between the actual and expected NTP timestamps at the PPS signals. With the previous 8 ns sampling without sawtooth correction it reached around -26 to -27, and now instead between -29 and -30. Are there adverse effects of having a dynamically varying NTP precision field? Cheers, Håkan On Sun, 12 Feb 2023, Bob Camp wrote: > Hi > > You don’t have to spend what the F9T’s cost simply to knock down the jitter. There are a > number of uBlox modules that have sawtooth correction data and cost < $40 mounted on > on a board. > > Bob > >> On Feb 12, 2023, at 6:51 AM, Håkan T Johansson <f96hajo@chalmers.se> wrote: >> >> >> Hi, >> >> perhaps the uBlox ZED-F9T would be a suitable choice, on a RCB-F9T board? >> That looks like 8 ns jitter, and the UBX-TIM-TP message should give the sawtooth. >> >> A 0.5 ns sampler I actually have on the FPGA. >> >> Cheers, >> Håkan >> >> >> On Sun, 12 Feb 2023, Ed Marciniak wrote: >> >>> Your mediatek GPS receiver is probably a really lousy pick for low jitter. >>> There are options from Navspark like the NS-T, other receiving chips/modules >>> from the same, as well as some uBlox parts that would do better. >>> There’s options with under 20ns jitter on those, and if memory serves >>> there’s one that’s available that with a good sky view and antenna might be >>> more like 8ns jitter. >>> Get Outlook for iOS >>> ____________________________________________________________________________ >>> From: Bob kb8tq via time-nuts <time-nuts@lists.febo.com> >>> Sent: Saturday, February 11, 2023 4:38:23 PM >>> To: Discussion of precise time and frequency measurement >>> <time-nuts@lists.febo.com> >>> Cc: Håkan T Johansson <f96hajo@chalmers.se>; Bob kb8tq <kb8tq@n1k.org> >>> Subject: [time-nuts] Re: FPGA-based GPS NTP server project >>> Hi >>> If you want to get the short term jitter down to around a second or so, >>> set it up with a GPS module that puts out a sawtooth correction. You >>> also need to get the Arty A7 measuring at the 1 ns level. That’s do-able >>> without insane amounts of effort. >>> Bob >>>> On Feb 11, 2023, at 4:09 AM, Håkan T Johansson via time-nuts >>> <time-nuts@lists.febo.com> wrote: >>>> >>>> >>>> Hi, >>>> >>>> I have a NTP server project based on a Digilent Arty A7 FPGA board with a >>> MediaTek GPS MT3329. Board-to-board NTP tests over network show about 20 ns >>> jitter, with long-term wanders of 100 ns, presumably due to my limited >>> sky-view. More details: >>>> >>>> http://fy.chalmers.se/~f96hajo/fakernet/board_Arty_A7-35-GPS-NTP.html >>>> >>>> Cheers, >>>> Håkan >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>> To unsubscribe send an email to time-nuts-leave@lists.febo.com >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe send an email to time-nuts-leave@lists.febo.com > >