Re: [time-nuts] U-blox teaser

[Dana Whitlow]

Thanks for the link, Bob.  I got to know both Victor Zhang and Mike
Lombardi during my
stay at Arecibo, but to my regret have never met either in person.

Dana


On Sat, Feb 27, 2021 at 6:01 PM Bob kb8tq  wrote:

> Hi
>
>
>
> > On Feb 27, 2021, at 11:18 AM, Dana Whitlow 
> wrote:
> >
> > Thanks, Bob.
> >
> > It seems to me that, depending on the positions of sats visible to one's
> GPS
> > antenna and the spatial distribution of free electron density in the
> > ionosphere,
> > the ionospheric contribution to position errors could sometimes largely
> > cancel.
> > But that observation may (or may not) reflect strongly on one's ability
> to
> > get
> > accurate absolute time from GPS on "average" days.
> >
> > During my Arecibo Observatory days we used NIST's TMAS service to keep
> > our H-maser-based station clock synced with UTC.  Our user community
> > (mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
> > 100ns
> > accuracy, so I tried to do better by keeping things well within +/- 50 ns
> > during
> > my reign.  IIRC, NIST was claiming that TMAS could produce results mostly
> > within about +/- 20 ns.
> >
> > To be honest I'm baffled by how time transfer much better than that could
> > be achieved in practice.
>
> One way (mentioned about a month back on the list) is a two way transfer
> via satellite. The “delay is equal in both directions” assumption is
> pretty good
> in this case. Once you have that as a baseline, you can measure the
> performance
> of other approaches.
>
> One of *many* starting points to rumble down this rabbit hole:
>
>
> https://www.nist.gov/pml/time-and-frequency-division/time-services/common-view-gps-time-transfer
> <
> https://www.nist.gov/pml/time-and-frequency-division/time-services/common-view-gps-time-transfer
> >
>
> I would suggest starting with David Allan’s paper (referenced in the link
> above) as a
> pretty good starting point.
>
> Bob
>
> >
> > Regarding Q3, yes I'm aware that *some* GPS receivers do the estimation
> of
> > ionospheric delay.  What I was asking was:  Do any of the relatively
> > inexpensive
> > receivers to which we time-nuts have access do this?  Here I'm speaking
> of
> > those being sold for no more than a few hundred USD.
> >
> > Dana
> >
> >
> >
> > On Sat, Feb 27, 2021 at 9:08 AM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >>
> >>
> >>> On Feb 27, 2021, at 9:41 AM, Dana Whitlow 
> wrote:
> >>>
> >>> I've long understood that ionospheric delays and variations thereof
> lead
> >> to
> >>> *position*
> >>> uncertainties in GPS navigation receivers, to the tune of perhaps 10m
> >>> (2DRMS IIRC).,
> >>> and that these are said to constitute the single largest GPS error
> >> source.
> >>>
> >>> Q1: Would this not imply timing errors of comparable magnitude (10's of
> >>> nsec)
> >>>  for a single band GPS?
> >>
> >> Once all the signals “hit” the antenna, the delays are mostly common
> mode.
> >> Instead of showing up as a position error, they show up as an error in
> the
> >> time estimate. Since time is one of the things you estimate in the
> >> solution
> >> (along with X,Y, and Z) it get’s it’s own independent solution.
> >>>
> >>> Q2: Why have I not seen this issue raised in connection with the
> present
> >>> discussion
> >>> about achievable absolute timing accuracy?
> >>
> >> GPS time transfer is often done to the sub-ns level. There are a number
> of
> >> papers on this.
> >>
> >>>
> >>> Q3: Do any of the "modern" timing GPS receivers available to civilians
> do
> >>> dual-band
> >>> reception in a way that includes estimation of (and correction for)
> >>> said delays and
> >>> their variations?  I know that Garmin, for one, is now selling
> L1/L5
> >>> handheld GPS
> >>> receivers (GPSMAP66sr and GPSMAP65s), but I've seen no indication
> >>> that these
> >>> units make any attempt at doing such corrections.
> >>
> >> Yes, some receivers do an estimate of ionospheric delay based on the
> >> variation of that delay with frequency. This does not help with
> >> tropospheric
> >> delay or all of the various “common mode” issues we have been talking
> >> about.
> >> It is also unclear how the “unknown” timing variation between the bands
> >> due to the antenna impacts these solutions…..
> >>
> >> Bob
> >>
> >>>
> >>> Dana
> >>>
> >>>
> >>>
> >>> On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq  wrote:
> >>>
>  Hi
> 
>  The same 20 or so ns delay in a saw would also apply to the
>  saw (or tight filter) in some timing antennas. It also would apply
>  to the saw(s) in some modules. Even if the tolerance is “only”
>  a couple ns on each of them, you *could* have 3 or more in the
>  chain.
> 
>  Lots of numbers to crunch to get to 5 ns “absolute”. One could go
>  grab a GPS simulator and start poking. First step would be to find
>  a simulator that is spec’d for a < 5 ns tolerance on the PPS into
>  GPS out. I do believe that rules out the eBay marvels that some
>  

Re: [time-nuts] U-blox teaser

[Bob kb8tq]

Hi



> On Feb 27, 2021, at 11:18 AM, Dana Whitlow  wrote:
> 
> Thanks, Bob.
> 
> It seems to me that, depending on the positions of sats visible to one's GPS
> antenna and the spatial distribution of free electron density in the
> ionosphere,
> the ionospheric contribution to position errors could sometimes largely
> cancel.
> But that observation may (or may not) reflect strongly on one's ability to
> get
> accurate absolute time from GPS on "average" days.
> 
> During my Arecibo Observatory days we used NIST's TMAS service to keep
> our H-maser-based station clock synced with UTC.  Our user community
> (mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
> 100ns
> accuracy, so I tried to do better by keeping things well within +/- 50 ns
> during
> my reign.  IIRC, NIST was claiming that TMAS could produce results mostly
> within about +/- 20 ns.
> 
> To be honest I'm baffled by how time transfer much better than that could
> be achieved in practice.

One way (mentioned about a month back on the list) is a two way transfer 
via satellite. The “delay is equal in both directions” assumption is pretty good
in this case. Once you have that as a baseline, you can measure the performance
of other approaches. 

One of *many* starting points to rumble down this rabbit hole:

https://www.nist.gov/pml/time-and-frequency-division/time-services/common-view-gps-time-transfer
 


I would suggest starting with David Allan’s paper (referenced in the link 
above) as a 
pretty good starting point.

Bob

> 
> Regarding Q3, yes I'm aware that *some* GPS receivers do the estimation of
> ionospheric delay.  What I was asking was:  Do any of the relatively
> inexpensive
> receivers to which we time-nuts have access do this?  Here I'm speaking of
> those being sold for no more than a few hundred USD.
> 
> Dana
> 
> 
> 
> On Sat, Feb 27, 2021 at 9:08 AM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> 
>> 
>>> On Feb 27, 2021, at 9:41 AM, Dana Whitlow  wrote:
>>> 
>>> I've long understood that ionospheric delays and variations thereof lead
>> to
>>> *position*
>>> uncertainties in GPS navigation receivers, to the tune of perhaps 10m
>>> (2DRMS IIRC).,
>>> and that these are said to constitute the single largest GPS error
>> source.
>>> 
>>> Q1: Would this not imply timing errors of comparable magnitude (10's of
>>> nsec)
>>>  for a single band GPS?
>> 
>> Once all the signals “hit” the antenna, the delays are mostly common mode.
>> Instead of showing up as a position error, they show up as an error in the
>> time estimate. Since time is one of the things you estimate in the
>> solution
>> (along with X,Y, and Z) it get’s it’s own independent solution.
>>> 
>>> Q2: Why have I not seen this issue raised in connection with the present
>>> discussion
>>> about achievable absolute timing accuracy?
>> 
>> GPS time transfer is often done to the sub-ns level. There are a number of
>> papers on this.
>> 
>>> 
>>> Q3: Do any of the "modern" timing GPS receivers available to civilians do
>>> dual-band
>>> reception in a way that includes estimation of (and correction for)
>>> said delays and
>>> their variations?  I know that Garmin, for one, is now selling L1/L5
>>> handheld GPS
>>> receivers (GPSMAP66sr and GPSMAP65s), but I've seen no indication
>>> that these
>>> units make any attempt at doing such corrections.
>> 
>> Yes, some receivers do an estimate of ionospheric delay based on the
>> variation of that delay with frequency. This does not help with
>> tropospheric
>> delay or all of the various “common mode” issues we have been talking
>> about.
>> It is also unclear how the “unknown” timing variation between the bands
>> due to the antenna impacts these solutions…..
>> 
>> Bob
>> 
>>> 
>>> Dana
>>> 
>>> 
>>> 
>>> On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq  wrote:
>>> 
 Hi
 
 The same 20 or so ns delay in a saw would also apply to the
 saw (or tight filter) in some timing antennas. It also would apply
 to the saw(s) in some modules. Even if the tolerance is “only”
 a couple ns on each of them, you *could* have 3 or more in the
 chain.
 
 Lots of numbers to crunch to get to 5 ns “absolute”. One could go
 grab a GPS simulator and start poking. First step would be to find
 a simulator that is spec’d for a < 5 ns tolerance on the PPS into
 GPS out. I do believe that rules out the eBay marvels that some
 of us have lying around …..
 
 Simpler answer would be a quick “clock trip” with your car full
 of 5071’s …… hour drive over to NIST and then back home.
 That sounds practical for most of us :) :)
 
 Bob
 
> On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR  wrote:
> 
> A while ago I tried doing a decidedly non-anechoic measurement with a
 VNA exciter going to a 1500 MHz ground plane and the receiver connected
>> to

Re: [time-nuts] U-blox teaser

[Hal Murray]

k8yumdoo...@gmail.com said:
> During my Arecibo Observatory days we used NIST's TMAS service to keep our
> H-maser-based station clock synced with UTC.  Our user community (mainly VLBI
> and pulsar timing people) seemed pretty satisfied with +/- 100ns accuracy, so
> I tried to do better by keeping things well within +/- 50 ns during my reign.
>  IIRC, NIST was claiming that TMAS could produce results mostly within about
> +/- 20 ns. 

I think the VLBI guys use the time from the clock at the receiver as a 
starting point.  What they need is a constant frequency.  They can work out 
the time offset.

Here is the example I heard about.  Suppose you have N antennas.  You need to 
know thir locations very accurately.  You can work out the location of one 
antenna if you point them all at a good point source and use N-1 antennas to 
work out where that point source is in the sky and the time/angle of the 
Earth's rotation.  Then you can solve for the position of the Nth antenna that 
gives the best fit.

I assume there are iterative approaches that can be used to refine the 
positions of multiple antennas.

Position is 3D.  Time is 1D so I assume the search is reasonably quick.

There are interesting similarities/dualities between GPS and VLBI.  With GPS, 
you have N transmitters and one receiver.  With VLBI, you have one transmitter 
and N receivers.  With VLBI, you can't work out the distance to the 
transmitter.  With GPS, you can't work out the length of the antenna cable.

-- 
These are my opinions.  I hate spam.




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Re: [time-nuts] U-blox teaser

[Tom Van Baak]

Dana,

> During my Arecibo Observatory days we used NIST's TMAS service to keep
> our H-maser-based station clock synced with UTC.

And before that, the observatory used Tom Clark's Oncore & SHOWTIME and 
later Rick Hambly's CNS clock & Tac32Plus, yes?


Rick continues to develop the CNS clock, having switched from the 
Motorola and iLotus receivers to u-blox T receivers. His papers are on 
cnssys.com or gpstime.com. Check out a recent one like:


"High-accuracy Time and Frequency in VLBI "
https://www.cnssys.com/files/TOW/High-accuracy_Time_and_Frequency_in_VLBI_2019_sem.pdf

Bonus: lots of graphs and photos, masers, receivers, etc.

Main publication page: https://www.cnssys.com/publications.php

Check out the performance he's getting. This is with a 6T. That's not 
dual-frequency or multi-constellation. Just plain old L1 GPS. It's way 
better than +/- 20 ns. So I'm really confused by what you're saying 
below. Did Arecibo get rid of the CNS clocks?


/tvb


On 2/27/2021 8:18 AM, Dana Whitlow wrote:

Thanks, Bob.

It seems to me that, depending on the positions of sats visible to one's GPS
antenna and the spatial distribution of free electron density in the
ionosphere,
the ionospheric contribution to position errors could sometimes largely
cancel.
But that observation may (or may not) reflect strongly on one's ability to
get
accurate absolute time from GPS on "average" days.

During my Arecibo Observatory days we used NIST's TMAS service to keep
our H-maser-based station clock synced with UTC.  Our user community
(mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
100ns
accuracy, so I tried to do better by keeping things well within +/- 50 ns
during
my reign.  IIRC, NIST was claiming that TMAS could produce results mostly
within about +/- 20 ns.

To be honest I'm baffled by how time transfer much better than that could
be achieved in practice.

Regarding Q3, yes I'm aware that *some* GPS receivers do the estimation of
ionospheric delay.  What I was asking was:  Do any of the relatively
inexpensive
receivers to which we time-nuts have access do this?  Here I'm speaking of
those being sold for no more than a few hundred USD.

Dana



On Sat, Feb 27, 2021 at 9:08 AM Bob kb8tq  wrote:


Hi




On Feb 27, 2021, at 9:41 AM, Dana Whitlow  wrote:

I've long understood that ionospheric delays and variations thereof lead

to

*position*
uncertainties in GPS navigation receivers, to the tune of perhaps 10m
(2DRMS IIRC).,
and that these are said to constitute the single largest GPS error

source.

Q1: Would this not imply timing errors of comparable magnitude (10's of
nsec)
   for a single band GPS?

Once all the signals “hit” the antenna, the delays are mostly common mode.
Instead of showing up as a position error, they show up as an error in the
time estimate. Since time is one of the things you estimate in the
solution
(along with X,Y, and Z) it get’s it’s own independent solution.

Q2: Why have I not seen this issue raised in connection with the present
discussion
  about achievable absolute timing accuracy?

GPS time transfer is often done to the sub-ns level. There are a number of
papers on this.


Q3: Do any of the "modern" timing GPS receivers available to civilians do
dual-band
  reception in a way that includes estimation of (and correction for)
said delays and
  their variations?  I know that Garmin, for one, is now selling L1/L5
handheld GPS
  receivers (GPSMAP66sr and GPSMAP65s), but I've seen no indication
that these
  units make any attempt at doing such corrections.

Yes, some receivers do an estimate of ionospheric delay based on the
variation of that delay with frequency. This does not help with
tropospheric
delay or all of the various “common mode” issues we have been talking
about.
It is also unclear how the “unknown” timing variation between the bands
due to the antenna impacts these solutions…..

Bob


Dana



On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq  wrote:


Hi

The same 20 or so ns delay in a saw would also apply to the
saw (or tight filter) in some timing antennas. It also would apply
to the saw(s) in some modules. Even if the tolerance is “only”
a couple ns on each of them, you *could* have 3 or more in the
chain.

Lots of numbers to crunch to get to 5 ns “absolute”. One could go
grab a GPS simulator and start poking. First step would be to find
a simulator that is spec’d for a < 5 ns tolerance on the PPS into
GPS out. I do believe that rules out the eBay marvels that some
of us have lying around …..

Simpler answer would be a quick “clock trip” with your car full
of 5071’s …… hour drive over to NIST and then back home.
That sounds practical for most of us :) :)

Bob


On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR  wrote:

A while ago I tried doing a decidedly non-anechoic measurement with a

VNA exciter going to a 1500 MHz ground plane and the receiver connected

to

the antenna (with a known delay cable) and I got a similar result, but

Re: [time-nuts] U-blox teaser

[Magnus Danielson]

Hi,

On 2021-02-27 17:18, Dana Whitlow wrote:
> Thanks, Bob.
>
> It seems to me that, depending on the positions of sats visible to one's GPS
> antenna and the spatial distribution of free electron density in the
> ionosphere,
> the ionospheric contribution to position errors could sometimes largely
> cancel.
> But that observation may (or may not) reflect strongly on one's ability to
> get
> accurate absolute time from GPS on "average" days.
>
> During my Arecibo Observatory days we used NIST's TMAS service to keep
> our H-maser-based station clock synced with UTC.  Our user community
> (mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
> 100ns
> accuracy, so I tried to do better by keeping things well within +/- 50 ns
> during
> my reign.  IIRC, NIST was claiming that TMAS could produce results mostly
> within about +/- 20 ns.
>
> To be honest I'm baffled by how time transfer much better than that could
> be achieved in practice.
>
> Regarding Q3, yes I'm aware that *some* GPS receivers do the estimation of
> ionospheric delay.  What I was asking was:  Do any of the relatively
> inexpensive
> receivers to which we time-nuts have access do this?  Here I'm speaking of
> those being sold for no more than a few hundred USD.

The uBlox F9 and Septentrio Mosaic does this. They output observables
such that good realtime and postprocessing can be achieved. By doing
double frequency, you can do trivial ionspheric delay observation and
compensation of that observation, such that both L1 and L2 can be
compensated. This way you can compensate with actual observed ionspheric
delay rather than using the Klobuchar model which on average only
removes half the ionspheric error. Also, that you get both code and
phase observations helps. All contributes significantly to push things
down. At the same time, doing this for as many satellites as a L1 only
receiver do provide more observables and more precision. Antenna and
reflections end up being more of a challenge in addition to calibration,
but it is worth the next level of improvement to push the errors towards
1 ns or sub 1 ns that you find in metrology type of comparisons. With
the F9 and Mosaic, the price of such receivers just dropped significantly.

TMAS is built with older type of receiver, but I suspect they will be
interested in upgrading for the next generation, as things push the
limit for what is possible on reasonable budget.

Speaking of which, I need to do some work on that. :)

Cheers,
Magnus


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Re: [time-nuts] U-blox teaser

[Lux, Jim]

On 2/27/21 8:18 AM, Dana Whitlow wrote:

Thanks, Bob.

It seems to me that, depending on the positions of sats visible to one's GPS
antenna and the spatial distribution of free electron density in the
ionosphere,
the ionospheric contribution to position errors could sometimes largely
cancel.
But that observation may (or may not) reflect strongly on one's ability to
get
accurate absolute time from GPS on "average" days.

During my Arecibo Observatory days we used NIST's TMAS service to keep
our H-maser-based station clock synced with UTC.  Our user community
(mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
100ns
accuracy, so I tried to do better by keeping things well within +/- 50 ns
during
my reign.  IIRC, NIST was claiming that TMAS could produce results mostly
within about +/- 20 ns.

To be honest I'm baffled by how time transfer much better than that could
be achieved in practice.

Regarding Q3, yes I'm aware that *some* GPS receivers do the estimation of
ionospheric delay.  What I was asking was:  Do any of the relatively
inexpensive
receivers to which we time-nuts have access do this?  Here I'm speaking of
those being sold for no more than a few hundred USD.

Dana

If it does dual frequency, then it probably compensates for the 
ionosphere. The algorithm isn't complex, and really, there's no reason 
to do dual or multiple frequency otherwise - You can get plenty of 
satellites with a L1 only, so the increased number of observables, 
alone, isn't a good reason for dual frequency.




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Re: [time-nuts] U-blox teaser

[Dana Whitlow]

Thanks, Bob.

It seems to me that, depending on the positions of sats visible to one's GPS
antenna and the spatial distribution of free electron density in the
ionosphere,
the ionospheric contribution to position errors could sometimes largely
cancel.
But that observation may (or may not) reflect strongly on one's ability to
get
accurate absolute time from GPS on "average" days.

During my Arecibo Observatory days we used NIST's TMAS service to keep
our H-maser-based station clock synced with UTC.  Our user community
(mainly VLBI and pulsar timing people) seemed pretty satisfied with +/-
100ns
accuracy, so I tried to do better by keeping things well within +/- 50 ns
during
my reign.  IIRC, NIST was claiming that TMAS could produce results mostly
within about +/- 20 ns.

To be honest I'm baffled by how time transfer much better than that could
be achieved in practice.

Regarding Q3, yes I'm aware that *some* GPS receivers do the estimation of
ionospheric delay.  What I was asking was:  Do any of the relatively
inexpensive
receivers to which we time-nuts have access do this?  Here I'm speaking of
those being sold for no more than a few hundred USD.

Dana



On Sat, Feb 27, 2021 at 9:08 AM Bob kb8tq  wrote:

> Hi
>
>
>
> > On Feb 27, 2021, at 9:41 AM, Dana Whitlow  wrote:
> >
> > I've long understood that ionospheric delays and variations thereof lead
> to
> > *position*
> > uncertainties in GPS navigation receivers, to the tune of perhaps 10m
> > (2DRMS IIRC).,
> > and that these are said to constitute the single largest GPS error
> source.
> >
> > Q1: Would this not imply timing errors of comparable magnitude (10's of
> > nsec)
> >   for a single band GPS?
>
> Once all the signals “hit” the antenna, the delays are mostly common mode.
> Instead of showing up as a position error, they show up as an error in the
> time estimate. Since time is one of the things you estimate in the
> solution
> (along with X,Y, and Z) it get’s it’s own independent solution.
> >
> > Q2: Why have I not seen this issue raised in connection with the present
> > discussion
> >  about achievable absolute timing accuracy?
>
> GPS time transfer is often done to the sub-ns level. There are a number of
> papers on this.
>
> >
> > Q3: Do any of the "modern" timing GPS receivers available to civilians do
> > dual-band
> >  reception in a way that includes estimation of (and correction for)
> > said delays and
> >  their variations?  I know that Garmin, for one, is now selling L1/L5
> > handheld GPS
> >  receivers (GPSMAP66sr and GPSMAP65s), but I've seen no indication
> > that these
> >  units make any attempt at doing such corrections.
>
> Yes, some receivers do an estimate of ionospheric delay based on the
> variation of that delay with frequency. This does not help with
> tropospheric
> delay or all of the various “common mode” issues we have been talking
> about.
> It is also unclear how the “unknown” timing variation between the bands
> due to the antenna impacts these solutions…..
>
> Bob
>
> >
> > Dana
> >
> >
> >
> > On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> The same 20 or so ns delay in a saw would also apply to the
> >> saw (or tight filter) in some timing antennas. It also would apply
> >> to the saw(s) in some modules. Even if the tolerance is “only”
> >> a couple ns on each of them, you *could* have 3 or more in the
> >> chain.
> >>
> >> Lots of numbers to crunch to get to 5 ns “absolute”. One could go
> >> grab a GPS simulator and start poking. First step would be to find
> >> a simulator that is spec’d for a < 5 ns tolerance on the PPS into
> >> GPS out. I do believe that rules out the eBay marvels that some
> >> of us have lying around …..
> >>
> >> Simpler answer would be a quick “clock trip” with your car full
> >> of 5071’s …… hour drive over to NIST and then back home.
> >> That sounds practical for most of us :) :)
> >>
> >> Bob
> >>
> >>> On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR  wrote:
> >>>
> >>> A while ago I tried doing a decidedly non-anechoic measurement with a
> >> VNA exciter going to a 1500 MHz ground plane and the receiver connected
> to
> >> the antenna (with a known delay cable) and I got a similar result, but
> >> there was enough noise that I didn't think I could nail it down to
> within
> >> 10 ns.
> >>>
> >>> I've also measured GPS antenna splitters and they tend to have 20-ish
> ns
> >> delays, mainly due to the SAW filters.  I did surgery on an HP splitter
> to
> >> remove the filters so it could be used for L1 and L2 and that dropped
> the
> >> delay down to only 1 or 2 ns.
> >>>
> >>> So there's definitely lots of stuff to calibrate if you want to get
> >> accurate time transfer.
> >>>
> >>> John
> >>> 
> >>>
> >>> On 2/26/21 8:02 PM, Michael Wouters wrote:
>  Typical L1 antenna delays range from 20 to 70 ns.
>  I know of only one antenna for which a delay is given by the vendor
> and
> >> the
>  technique used was just 

Re: [time-nuts] U-blox teaser

[Bob kb8tq]

Hi



> On Feb 27, 2021, at 9:41 AM, Dana Whitlow  wrote:
> 
> I've long understood that ionospheric delays and variations thereof lead to
> *position*
> uncertainties in GPS navigation receivers, to the tune of perhaps 10m
> (2DRMS IIRC).,
> and that these are said to constitute the single largest GPS error source.
> 
> Q1: Would this not imply timing errors of comparable magnitude (10's of
> nsec)
>   for a single band GPS?

Once all the signals “hit” the antenna, the delays are mostly common mode.
Instead of showing up as a position error, they show up as an error in the 
time estimate. Since time is one of the things you estimate in the solution 
(along with X,Y, and Z) it get’s it’s own independent solution. 
> 
> Q2: Why have I not seen this issue raised in connection with the present
> discussion
>  about achievable absolute timing accuracy?

GPS time transfer is often done to the sub-ns level. There are a number of 
papers on this. 

> 
> Q3: Do any of the "modern" timing GPS receivers available to civilians do
> dual-band
>  reception in a way that includes estimation of (and correction for)
> said delays and
>  their variations?  I know that Garmin, for one, is now selling L1/L5
> handheld GPS
>  receivers (GPSMAP66sr and GPSMAP65s), but I've seen no indication
> that these
>  units make any attempt at doing such corrections.

Yes, some receivers do an estimate of ionospheric delay based on the 
variation of that delay with frequency. This does not help with tropospheric 
delay or all of the various “common mode” issues we have been talking about. 
It is also unclear how the “unknown” timing variation between the bands
due to the antenna impacts these solutions…..

Bob

> 
> Dana
> 
> 
> 
> On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> The same 20 or so ns delay in a saw would also apply to the
>> saw (or tight filter) in some timing antennas. It also would apply
>> to the saw(s) in some modules. Even if the tolerance is “only”
>> a couple ns on each of them, you *could* have 3 or more in the
>> chain.
>> 
>> Lots of numbers to crunch to get to 5 ns “absolute”. One could go
>> grab a GPS simulator and start poking. First step would be to find
>> a simulator that is spec’d for a < 5 ns tolerance on the PPS into
>> GPS out. I do believe that rules out the eBay marvels that some
>> of us have lying around …..
>> 
>> Simpler answer would be a quick “clock trip” with your car full
>> of 5071’s …… hour drive over to NIST and then back home.
>> That sounds practical for most of us :) :)
>> 
>> Bob
>> 
>>> On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR  wrote:
>>> 
>>> A while ago I tried doing a decidedly non-anechoic measurement with a
>> VNA exciter going to a 1500 MHz ground plane and the receiver connected to
>> the antenna (with a known delay cable) and I got a similar result, but
>> there was enough noise that I didn't think I could nail it down to within
>> 10 ns.
>>> 
>>> I've also measured GPS antenna splitters and they tend to have 20-ish ns
>> delays, mainly due to the SAW filters.  I did surgery on an HP splitter to
>> remove the filters so it could be used for L1 and L2 and that dropped the
>> delay down to only 1 or 2 ns.
>>> 
>>> So there's definitely lots of stuff to calibrate if you want to get
>> accurate time transfer.
>>> 
>>> John
>>> 
>>> 
>>> On 2/26/21 8:02 PM, Michael Wouters wrote:
 Typical L1 antenna delays range from 20 to 70 ns.
 I know of only one antenna for which a delay is given by the vendor and
>> the
 technique used was just to measure the electronic delay ie by injecting
>> a
 signal into the circuit. To do it properly, you need a setup in a
>> microwave
 anechoic chamber with transmitting antenna etc. The practical difference
 may be small though, 1 or 2 ns ( sample of one antenna!).
 Cheers
 Michael
 On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR 
>> wrote:
> They're claiming "even better than" 5 ns for relative time, which given
> the 4 ns jitter seems at least sort-of reasonable.  But until someone
> shows me otherwise, I'm still thinking that getting better than 25 ns
> absolute accuracy is a pretty good day's work.
> 
> John
> 
> 
> On 2/26/21 5:26 PM, Bob kb8tq wrote:
>> Hi
>> 
>> I can’t think of many antennas (multi band or single band) that claim
>> to
> know their
>> delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns
>> is
> quite good.
>> Same thing with delay ripple, you see specs out to around 15 ns on a
>> lot
> of antennas.
>> None of this is getting you to the actual total delay of the antenna.
> It’s a pretty good
>> bet that number is a bit larger than either of these.
>> 
>> Some of the ripple probably comes out in the standard modeling. I’m
>> not
> sure that
>> the differential delay is taken out that way. Total delay, not taken
>> out

Re: [time-nuts] U-blox teaser

[Dana Whitlow]

I've long understood that ionospheric delays and variations thereof lead to
*position*
uncertainties in GPS navigation receivers, to the tune of perhaps 10m
(2DRMS IIRC).,
and that these are said to constitute the single largest GPS error source.

Q1: Would this not imply timing errors of comparable magnitude (10's of
nsec)
   for a single band GPS?

Q2: Why have I not seen this issue raised in connection with the present
discussion
  about achievable absolute timing accuracy?

Q3: Do any of the "modern" timing GPS receivers available to civilians do
dual-band
  reception in a way that includes estimation of (and correction for)
said delays and
  their variations?  I know that Garmin, for one, is now selling L1/L5
handheld GPS
  receivers (GPSMAP66sr and GPSMAP65s), but I've seen no indication
that these
  units make any attempt at doing such corrections.

Dana



On Sat, Feb 27, 2021 at 7:43 AM Bob kb8tq  wrote:

> Hi
>
> The same 20 or so ns delay in a saw would also apply to the
> saw (or tight filter) in some timing antennas. It also would apply
> to the saw(s) in some modules. Even if the tolerance is “only”
> a couple ns on each of them, you *could* have 3 or more in the
> chain.
>
> Lots of numbers to crunch to get to 5 ns “absolute”. One could go
> grab a GPS simulator and start poking. First step would be to find
> a simulator that is spec’d for a < 5 ns tolerance on the PPS into
> GPS out. I do believe that rules out the eBay marvels that some
> of us have lying around …..
>
> Simpler answer would be a quick “clock trip” with your car full
> of 5071’s …… hour drive over to NIST and then back home.
> That sounds practical for most of us :) :)
>
> Bob
>
> > On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR  wrote:
> >
> > A while ago I tried doing a decidedly non-anechoic measurement with a
> VNA exciter going to a 1500 MHz ground plane and the receiver connected to
> the antenna (with a known delay cable) and I got a similar result, but
> there was enough noise that I didn't think I could nail it down to within
> 10 ns.
> >
> > I've also measured GPS antenna splitters and they tend to have 20-ish ns
> delays, mainly due to the SAW filters.  I did surgery on an HP splitter to
> remove the filters so it could be used for L1 and L2 and that dropped the
> delay down to only 1 or 2 ns.
> >
> > So there's definitely lots of stuff to calibrate if you want to get
> accurate time transfer.
> >
> > John
> > 
> >
> > On 2/26/21 8:02 PM, Michael Wouters wrote:
> >> Typical L1 antenna delays range from 20 to 70 ns.
> >> I know of only one antenna for which a delay is given by the vendor and
> the
> >> technique used was just to measure the electronic delay ie by injecting
> a
> >> signal into the circuit. To do it properly, you need a setup in a
> microwave
> >> anechoic chamber with transmitting antenna etc. The practical difference
> >> may be small though, 1 or 2 ns ( sample of one antenna!).
> >> Cheers
> >> Michael
> >> On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR 
> wrote:
> >>> They're claiming "even better than" 5 ns for relative time, which given
> >>> the 4 ns jitter seems at least sort-of reasonable.  But until someone
> >>> shows me otherwise, I'm still thinking that getting better than 25 ns
> >>> absolute accuracy is a pretty good day's work.
> >>>
> >>> John
> >>> 
> >>>
> >>> On 2/26/21 5:26 PM, Bob kb8tq wrote:
>  Hi
> 
>  I can’t think of many antennas (multi band or single band) that claim
> to
> >>> know their
>  delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns
> is
> >>> quite good.
>  Same thing with delay ripple, you see specs out to around 15 ns on a
> lot
> >>> of antennas.
>  None of this is getting you to the actual total delay of the antenna.
> >>> It’s a pretty good
>  bet that number is a bit larger than either of these.
> 
>  Some of the ripple probably comes out in the standard modeling. I’m
> not
> >>> sure that
>  the differential delay is taken out that way. Total delay, not taken
> out
> >>> in any obvious
>  fashion ( at least that I can see). If the F9 has a built in antenna
> >>> database, that’s not
>  mentioned in the doc’s. Any benefit from the corrections would have to
> >>> be part of
>  post processing.
> 
>  No, that’s not the same as talking about the F9 it’s self doing X ns,
> >>> but it would be part
>  of any practical system trying to get close to 5 ns absolute accuracy.
> 
>  5 ns *relative* accuracy between two F9’s? I probably could buy that
> if
> >>> the appropriate
>  one sigma / on a clear day / with the wind in the right direction sort
> >>> of qualifiers are
>  attached.
> 
>  Bob
> 
> > On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR 
> wrote:
> >
> > It's interesting that they talk about the F9 receivers offering 5 ns
> >>> absolute time accuracy.  Does anyone know of tests confirming 

Re: [time-nuts] U-blox teaser

[Bob kb8tq]

Hi

The same 20 or so ns delay in a saw would also apply to the 
saw (or tight filter) in some timing antennas. It also would apply
to the saw(s) in some modules. Even if the tolerance is “only”
a couple ns on each of them, you *could* have 3 or more in the
chain.

Lots of numbers to crunch to get to 5 ns “absolute”. One could go 
grab a GPS simulator and start poking. First step would be to find
a simulator that is spec’d for a < 5 ns tolerance on the PPS into 
GPS out. I do believe that rules out the eBay marvels that some 
of us have lying around …..

Simpler answer would be a quick “clock trip” with your car full
of 5071’s …… hour drive over to NIST and then back home. 
That sounds practical for most of us :) :)

Bob

> On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR  wrote:
> 
> A while ago I tried doing a decidedly non-anechoic measurement with a VNA 
> exciter going to a 1500 MHz ground plane and the receiver connected to the 
> antenna (with a known delay cable) and I got a similar result, but there was 
> enough noise that I didn't think I could nail it down to within 10 ns.
> 
> I've also measured GPS antenna splitters and they tend to have 20-ish ns 
> delays, mainly due to the SAW filters.  I did surgery on an HP splitter to 
> remove the filters so it could be used for L1 and L2 and that dropped the 
> delay down to only 1 or 2 ns.
> 
> So there's definitely lots of stuff to calibrate if you want to get accurate 
> time transfer.
> 
> John
> 
> 
> On 2/26/21 8:02 PM, Michael Wouters wrote:
>> Typical L1 antenna delays range from 20 to 70 ns.
>> I know of only one antenna for which a delay is given by the vendor and the
>> technique used was just to measure the electronic delay ie by injecting a
>> signal into the circuit. To do it properly, you need a setup in a microwave
>> anechoic chamber with transmitting antenna etc. The practical difference
>> may be small though, 1 or 2 ns ( sample of one antenna!).
>> Cheers
>> Michael
>> On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR  wrote:
>>> They're claiming "even better than" 5 ns for relative time, which given
>>> the 4 ns jitter seems at least sort-of reasonable.  But until someone
>>> shows me otherwise, I'm still thinking that getting better than 25 ns
>>> absolute accuracy is a pretty good day's work.
>>> 
>>> John
>>> 
>>> 
>>> On 2/26/21 5:26 PM, Bob kb8tq wrote:
 Hi
 
 I can’t think of many antennas (multi band or single band) that claim to
>>> know their
 delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is
>>> quite good.
 Same thing with delay ripple, you see specs out to around 15 ns on a lot
>>> of antennas.
 None of this is getting you to the actual total delay of the antenna.
>>> It’s a pretty good
 bet that number is a bit larger than either of these.
 
 Some of the ripple probably comes out in the standard modeling. I’m not
>>> sure that
 the differential delay is taken out that way. Total delay, not taken out
>>> in any obvious
 fashion ( at least that I can see). If the F9 has a built in antenna
>>> database, that’s not
 mentioned in the doc’s. Any benefit from the corrections would have to
>>> be part of
 post processing.
 
 No, that’s not the same as talking about the F9 it’s self doing X ns,
>>> but it would be part
 of any practical system trying to get close to 5 ns absolute accuracy.
 
 5 ns *relative* accuracy between two F9’s? I probably could buy that if
>>> the appropriate
 one sigma / on a clear day / with the wind in the right direction sort
>>> of qualifiers are
 attached.
 
 Bob
 
> On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR  wrote:
> 
> It's interesting that they talk about the F9 receivers offering 5 ns
>>> absolute time accuracy.  Does anyone know of tests confirming that, and
>>> what sort of care was required in the setup to get there?
> 
> John
> 
> 
> On 2/26/21 9:34 AM, Robert LaJeunesse wrote:
>> FWIW. No detailed content, and a rather quick read. "Five key trends
>>> in GPS".
>> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps
>> ___
>> time-nuts mailing list -- time-nuts@lists.febo.com
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>> and follow the instructions there.
> 
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
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> and follow the instructions there.
 
 
 ___
 time-nuts mailing list -- time-nuts@lists.febo.com
 To unsubscribe, go to
>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
 and follow the instructions there.
 
>>> 
>>> 

Re: [time-nuts] U-blox teaser

[John Ackermann N8UR]

A while ago I tried doing a decidedly non-anechoic measurement with a 
VNA exciter going to a 1500 MHz ground plane and the receiver connected 
to the antenna (with a known delay cable) and I got a similar result, 
but there was enough noise that I didn't think I could nail it down to 
within 10 ns.


I've also measured GPS antenna splitters and they tend to have 20-ish ns 
delays, mainly due to the SAW filters.  I did surgery on an HP splitter 
to remove the filters so it could be used for L1 and L2 and that dropped 
the delay down to only 1 or 2 ns.


So there's definitely lots of stuff to calibrate if you want to get 
accurate time transfer.


John


On 2/26/21 8:02 PM, Michael Wouters wrote:

Typical L1 antenna delays range from 20 to 70 ns.
I know of only one antenna for which a delay is given by the vendor and the
technique used was just to measure the electronic delay ie by injecting a
signal into the circuit. To do it properly, you need a setup in a microwave
anechoic chamber with transmitting antenna etc. The practical difference
may be small though, 1 or 2 ns ( sample of one antenna!).

Cheers
Michael

On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR  wrote:


They're claiming "even better than" 5 ns for relative time, which given
the 4 ns jitter seems at least sort-of reasonable.  But until someone
shows me otherwise, I'm still thinking that getting better than 25 ns
absolute accuracy is a pretty good day's work.

John


On 2/26/21 5:26 PM, Bob kb8tq wrote:

Hi

I can’t think of many antennas (multi band or single band) that claim to

know their

delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is

quite good.

Same thing with delay ripple, you see specs out to around 15 ns on a lot

of antennas.

None of this is getting you to the actual total delay of the antenna.

It’s a pretty good

bet that number is a bit larger than either of these.

Some of the ripple probably comes out in the standard modeling. I’m not

sure that

the differential delay is taken out that way. Total delay, not taken out

in any obvious

fashion ( at least that I can see). If the F9 has a built in antenna

database, that’s not

mentioned in the doc’s. Any benefit from the corrections would have to

be part of

post processing.

No, that’s not the same as talking about the F9 it’s self doing X ns,

but it would be part

of any practical system trying to get close to 5 ns absolute accuracy.

5 ns *relative* accuracy between two F9’s? I probably could buy that if

the appropriate

one sigma / on a clear day / with the wind in the right direction sort

of qualifiers are

attached.

Bob


On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR  wrote:

It's interesting that they talk about the F9 receivers offering 5 ns

absolute time accuracy.  Does anyone know of tests confirming that, and
what sort of care was required in the setup to get there?


John


On 2/26/21 9:34 AM, Robert LaJeunesse wrote:

FWIW. No detailed content, and a rather quick read. "Five key trends

in GPS".

https://www.u-blox.com/en/blogs/insights/five-key-trends-gps
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Re: [time-nuts] U-blox teaser

[Lux, Jim]

On 2/26/21 4:00 PM, John Ackermann N8UR wrote:
They're claiming "even better than" 5 ns for relative time, which 
given the 4 ns jitter seems at least sort-of reasonable.  But until 
someone shows me otherwise, I'm still thinking that getting better 
than 25 ns absolute accuracy is a pretty good day's work.


John




And if the jitter is uniformly distributed (i.e. 1 clock cycle of some 
sort) - then the sd is 1/sqrt(12) of the extremes, so a "max 
uncertainty" of 5ns, is more like a 1.5 ns 1 sigma.



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Re: [time-nuts] U-blox teaser

[Michael Wouters]

Typical L1 antenna delays range from 20 to 70 ns.
I know of only one antenna for which a delay is given by the vendor and the
technique used was just to measure the electronic delay ie by injecting a
signal into the circuit. To do it properly, you need a setup in a microwave
anechoic chamber with transmitting antenna etc. The practical difference
may be small though, 1 or 2 ns ( sample of one antenna!).

Cheers
Michael

On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR  wrote:

> They're claiming "even better than" 5 ns for relative time, which given
> the 4 ns jitter seems at least sort-of reasonable.  But until someone
> shows me otherwise, I'm still thinking that getting better than 25 ns
> absolute accuracy is a pretty good day's work.
>
> John
> 
>
> On 2/26/21 5:26 PM, Bob kb8tq wrote:
> > Hi
> >
> > I can’t think of many antennas (multi band or single band) that claim to
> know their
> > delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is
> quite good.
> > Same thing with delay ripple, you see specs out to around 15 ns on a lot
> of antennas.
> > None of this is getting you to the actual total delay of the antenna.
> It’s a pretty good
> > bet that number is a bit larger than either of these.
> >
> > Some of the ripple probably comes out in the standard modeling. I’m not
> sure that
> > the differential delay is taken out that way. Total delay, not taken out
> in any obvious
> > fashion ( at least that I can see). If the F9 has a built in antenna
> database, that’s not
> > mentioned in the doc’s. Any benefit from the corrections would have to
> be part of
> > post processing.
> >
> > No, that’s not the same as talking about the F9 it’s self doing X ns,
> but it would be part
> > of any practical system trying to get close to 5 ns absolute accuracy.
> >
> > 5 ns *relative* accuracy between two F9’s? I probably could buy that if
> the appropriate
> > one sigma / on a clear day / with the wind in the right direction sort
> of qualifiers are
> > attached.
> >
> > Bob
> >
> >> On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR  wrote:
> >>
> >> It's interesting that they talk about the F9 receivers offering 5 ns
> absolute time accuracy.  Does anyone know of tests confirming that, and
> what sort of care was required in the setup to get there?
> >>
> >> John
> >> 
> >>
> >> On 2/26/21 9:34 AM, Robert LaJeunesse wrote:
> >>> FWIW. No detailed content, and a rather quick read. "Five key trends
> in GPS".
> >>> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps
> >>> ___
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Re: [time-nuts] U-blox teaser

[John Ackermann]

That's how I'd interpret it.

⁣Get BlueMail for Android ​

On Feb 26, 2021, 7:42 PM, at 7:42 PM, Bob kb8tq  wrote:
>Hi
>
>Would not “absolute” timing be referenced to UTC? (or something
>similar)
>
>Bob
>
>> On Feb 26, 2021, at 5:37 PM, ed breya  wrote:
>> 
>> John, if you look back at the recent GPSDO discussion initiated by
>"dandober" in hpaligent keysight group, you'll see a post by Leo
>Bodnar, linking a Ublox model here
>> 
>>
>https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf
>> 
>> I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After
>I studied it some, I replied back
>> 
>> "Thanks Leo, that's a great example of what I've been picturing. This
>is from the data sheet, regarding the PPS output:
>> 
>> "After an initial phase of acquisition the time-pulse becomes
>essentially jitter-free, generated coherently from the built-in
>reference oscillator and guaranteeing an exact number of reference
>frequency cycles between each time-pulse."
>> 
>> It looks like this is an implementation of what we've talked about
>here before a few times, for saw-tooth error reduction. BTW I didn't
>call it "1PPS" above, because it can be programmed for different rates
>- I don't recall what they are.
>> 
>> BTW, did dandober ever sign up here?
>> 
>> Ed
>> 
>> 
>> 
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>
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Re: [time-nuts] U-blox teaser

[John Ackermann N8UR]

You have to be careful comparing the LEA-M8F with other GPS units.  It 
does have low jitter because the "TIMEPULSE" signal is derived from the 
TCXO which is locked to the GPS time mark.


But their claim of "essentially jitter free" depends on your definition 
of "essentially" -- attached is a comparison of LEA-M8F PPS jitter vs. 
NEO-M8T and ZED-F9T raw, and NEO-M8T and ZED-F9T sawtooth corrected PPS. 
 The M8F is definitely better than the raw M8T and even the raw F9T, 
but the corrected M8T and F9T are both much better than the M8F.  And 
the M8F does *not* have sawtooth correction available.


So, it's a neat implementation and has some applications (basically as a 
modest performance 30.72 MHz GPSDO), but TANSTAAFL.


John


On 2/26/21 5:37 PM, ed breya wrote:
John, if you look back at the recent GPSDO discussion initiated by 
"dandober" in hpaligent keysight group, you'll see a post by Leo Bodnar, 
linking a Ublox model here


https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf 



I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After I 
studied it some, I replied back


"Thanks Leo, that's a great example of what I've been picturing. This is 
from the data sheet, regarding the PPS output:


"After an initial phase of acquisition the time-pulse becomes 
essentially jitter-free, generated coherently from the built-in 
reference oscillator and guaranteeing an exact number of reference 
frequency cycles between each time-pulse."


It looks like this is an implementation of what we've talked about here 
before a few times, for saw-tooth error reduction. BTW I didn't call it 
"1PPS" above, because it can be programmed for different rates - I don't 
recall what they are.


BTW, did dandober ever sign up here?

Ed



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Re: [time-nuts] U-blox teaser

[John Ackermann N8UR]

They're claiming "even better than" 5 ns for relative time, which given 
the 4 ns jitter seems at least sort-of reasonable.  But until someone 
shows me otherwise, I'm still thinking that getting better than 25 ns 
absolute accuracy is a pretty good day's work.


John


On 2/26/21 5:26 PM, Bob kb8tq wrote:

Hi

I can’t think of many antennas (multi band or single band) that claim to know 
their
delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is quite 
good.
Same thing with delay ripple, you see specs out to around 15 ns on a lot of 
antennas.
None of this is getting you to the actual total delay of the antenna. It’s a 
pretty good
bet that number is a bit larger than either of these.

Some of the ripple probably comes out in the standard modeling. I’m not sure 
that
the differential delay is taken out that way. Total delay, not taken out in any 
obvious
fashion ( at least that I can see). If the F9 has a built in antenna database, 
that’s not
mentioned in the doc’s. Any benefit from the corrections would have to be part 
of
post processing.

No, that’s not the same as talking about the F9 it’s self doing X ns, but it 
would be part
of any practical system trying to get close to 5 ns absolute accuracy.

5 ns *relative* accuracy between two F9’s? I probably could buy that if the 
appropriate
one sigma / on a clear day / with the wind in the right direction sort of 
qualifiers are
attached.

Bob


On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR  wrote:

It's interesting that they talk about the F9 receivers offering 5 ns absolute 
time accuracy.  Does anyone know of tests confirming that, and what sort of 
care was required in the setup to get there?

John


On 2/26/21 9:34 AM, Robert LaJeunesse wrote:

FWIW. No detailed content, and a rather quick read. "Five key trends in GPS".
https://www.u-blox.com/en/blogs/insights/five-key-trends-gps
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Re: [time-nuts] U-blox teaser

[Bob kb8tq]

Hi

Would not “absolute” timing be referenced to UTC? (or something similar)

Bob

> On Feb 26, 2021, at 5:37 PM, ed breya  wrote:
> 
> John, if you look back at the recent GPSDO discussion initiated by "dandober" 
> in hpaligent keysight group, you'll see a post by Leo Bodnar, linking a Ublox 
> model here
> 
> https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf
> 
> I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After I 
> studied it some, I replied back
> 
> "Thanks Leo, that's a great example of what I've been picturing. This is from 
> the data sheet, regarding the PPS output:
> 
> "After an initial phase of acquisition the time-pulse becomes essentially 
> jitter-free, generated coherently from the built-in reference oscillator and 
> guaranteeing an exact number of reference frequency cycles between each 
> time-pulse."
> 
> It looks like this is an implementation of what we've talked about here 
> before a few times, for saw-tooth error reduction. BTW I didn't call it 
> "1PPS" above, because it can be programmed for different rates - I don't 
> recall what they are.
> 
> BTW, did dandober ever sign up here?
> 
> Ed
> 
> 
> 
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Re: [time-nuts] U-blox teaser

[ed breya]

John, if you look back at the recent GPSDO discussion initiated by 
"dandober" in hpaligent keysight group, you'll see a post by Leo Bodnar, 
linking a Ublox model here


https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf

I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After I 
studied it some, I replied back


"Thanks Leo, that's a great example of what I've been picturing. This is 
from the data sheet, regarding the PPS output:


"After an initial phase of acquisition the time-pulse becomes 
essentially jitter-free, generated coherently from the built-in 
reference oscillator and guaranteeing an exact number of reference 
frequency cycles between each time-pulse."


It looks like this is an implementation of what we've talked about here 
before a few times, for saw-tooth error reduction. BTW I didn't call it 
"1PPS" above, because it can be programmed for different rates - I don't 
recall what they are.


BTW, did dandober ever sign up here?

Ed



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Re: [time-nuts] U-blox teaser

[Bob kb8tq]

Hi

I can’t think of many antennas (multi band or single band) that claim to know 
their
delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is quite 
good. 
Same thing with delay ripple, you see specs out to around 15 ns on a lot of 
antennas.
None of this is getting you to the actual total delay of the antenna. It’s a 
pretty good
bet that number is a bit larger than either of these. 

Some of the ripple probably comes out in the standard modeling. I’m not sure 
that 
the differential delay is taken out that way. Total delay, not taken out in any 
obvious 
fashion ( at least that I can see). If the F9 has a built in antenna database, 
that’s not 
mentioned in the doc’s. Any benefit from the corrections would have to be part 
of 
post processing. 

No, that’s not the same as talking about the F9 it’s self doing X ns, but it 
would be part 
of any practical system trying to get close to 5 ns absolute accuracy. 

5 ns *relative* accuracy between two F9’s? I probably could buy that if the 
appropriate 
one sigma / on a clear day / with the wind in the right direction sort of 
qualifiers are
attached. 

Bob

> On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR  wrote:
> 
> It's interesting that they talk about the F9 receivers offering 5 ns absolute 
> time accuracy.  Does anyone know of tests confirming that, and what sort of 
> care was required in the setup to get there?
> 
> John
> 
> 
> On 2/26/21 9:34 AM, Robert LaJeunesse wrote:
>> FWIW. No detailed content, and a rather quick read. "Five key trends in GPS".
>> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps
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Re: [time-nuts] U-blox teaser

[John Ackermann N8UR]

It's interesting that they talk about the F9 receivers offering 5 ns 
absolute time accuracy.  Does anyone know of tests confirming that, and 
what sort of care was required in the setup to get there?


John


On 2/26/21 9:34 AM, Robert LaJeunesse wrote:

FWIW. No detailed content, and a rather quick read. "Five key trends in GPS".

https://www.u-blox.com/en/blogs/insights/five-key-trends-gps

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[time-nuts] U-blox teaser

[Robert LaJeunesse]

FWIW. No detailed content, and a rather quick read. "Five key trends in GPS".

https://www.u-blox.com/en/blogs/insights/five-key-trends-gps

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