Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Attila Kinali]

On Wed, 8 Nov 2017 14:24:08 -0600
"Chris Caudle"  wrote:

> On Wed, November 8, 2017 12:55 pm, Gary E. Miller wrote:
> > I knew about the errata, I left out that detail to see when someone
> > actually read my citation.
> 
> OK, I don't want to quibble about versions, and whether the "latest
> version" is 200H or 200H including errata, but I think we both agree that
> the currently operating performance would be described by the rollup
> document, i.e. the offset information for GPS time to UTC time should be
> within 20ns 1 sigma, as opposed to the older 90 ns 1 sigma description.

The GPS standard only specifies a _target_ value, what they want to achieve.
The actual value has been consistenly better than what is described in the
standard for decades. Why standard not updated, you ask? Because in a
standard you want to be conservative. People rely on that value and if
anything happens and for some reason that value gets much worse than usual,
you still want tto be within specs.


> > Do you now see how measured GPS time/location can be very precise, but
> > UTC from a GPS less so?  Have you read the entire 3.3.4?
> 
> Yes, and I do not really understand the "1 sigma" description.  Is the
> error really random?  I'm not sure how the term 1 sigma applies to error
> distributions other than a Gaussian distribution, so what "20 ns at 1
> sigma" really means moment to moment for the time value I get from a GPS
> receiver is not completely clear to me.  At a simplistic level I would
> interpret that 66% of the PPS ticks are within 20ns of the "true" UTC
> tick, 33+% could be farther away than 20ns from "true" second tick.

This is what it means. The distribution is not completely gaussian.
There are some periodic (12h, 24h, and various others) contents that
look more sinusoidal than random, but if you look at the raw distribution,
without extracting any of the periodic components, it looks quite gaussian.

 
> The general interest in GPS based time transfer covers a wide range of
> uses, so whether you actually care about absolute offset from UTC or not
> needs to be made more explicit in discussions about vaguely defined
> "performance."  

If you are really doing time transfer using GPS and you care about
performance. Then you are using at least common-in-view mode with some
heavy post-processing. This brings you close to a 5ns one-sigma uncertainty.
If you calibrate your GPS receivers frequently, you can get down to 200ps.
(over a few 100km baseline).

If you need better than that, you go to Timetech ( http://www.timetech.de/ )
and ask them to loan you one of the TWSTFT systems.


Attila Kinali



-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Attila Kinali]

On Tue, 7 Nov 2017 22:07:43 +
Leo Bodnar  wrote:

> Coincidentally, I have been testing relative phase difference of two GPS 
> clocks 
> http://www.leobodnar.com/shop/index.php?main_page=product_info=107_id=301
>  since Friday. 
> They are completely independent, including separate antennas and positioned a 
> few yards away from each other so ionospheric disturbances would affect both 
> units equally.  Devices use Ublox chipset.
> 
> Average phase difference did not change in four days since Friday but there 
> is phase wander within around 10ns.
> Here is a video of 4 hours worth of data.  One horizontal division is 20ns:
> 
> http://leobodnar.com/balloons/NTP/twoGPSclocks.mp4

Do you have this measurement with proper time-differences?
Ie like using a simple and cheap counter? That would be quite
a bit more interesting than a video of an osciloscope screen.

Attila kinali


-- 
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering.  -- The Doctor
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Chris Caudle]

On Wed, November 8, 2017 12:55 pm, Gary E. Miller wrote:
> I knew about the errata, I left out that detail to see when someone
> actually read my citation.

OK, I don't want to quibble about versions, and whether the "latest
version" is 200H or 200H including errata, but I think we both agree that
the currently operating performance would be described by the rollup
document, i.e. the offset information for GPS time to UTC time should be
within 20ns 1 sigma, as opposed to the older 90 ns 1 sigma description.

> So yes, UTC from a GPS is now 20 ns (one sigama).  What I said about
> +/- 13 ns being noise relative to the spec still applies.

Yes, and at that point I think you have to start getting into more precise
language about whether you care about worst case, average, or "typical"
performance.  One of the graphs that Tom referenced a day or two ago
seemed to show that the typical performance was better than 20ns, so is
20ns a guaranteed performance, a desired performance level (and better
than that is good), or the measured performance level?

> Do you now see how measured GPS time/location can be very precise, but
> UTC from a GPS less so?  Have you read the entire 3.3.4?

Yes, and I do not really understand the "1 sigma" description.  Is the
error really random?  I'm not sure how the term 1 sigma applies to error
distributions other than a Gaussian distribution, so what "20 ns at 1
sigma" really means moment to moment for the time value I get from a GPS
receiver is not completely clear to me.  At a simplistic level I would
interpret that 66% of the PPS ticks are within 20ns of the "true" UTC
tick, 33+% could be farther away than 20ns from "true" second tick.

The general interest in GPS based time transfer covers a wide range of
uses, so whether you actually care about absolute offset from UTC or not
needs to be made more explicit in discussions about vaguely defined
"performance."  I think in earlier emails there was some confusion about
what "performance" actually referenced, since in a lot of use cases a
fixed error offset from UTC is less important than varying offset, some
people just need a well defined second tick, so whether the position of
those ticks is within 2ns, 20ns, or 200ns of nominal UTC may not matter at
all.  Other uses may care about UTC, so there is not necessarily a one
size fits all single number for "performance" that everyone will agree
with.

-- 
Chris Caudle


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo Tom!

On Wed, 8 Nov 2017 09:31:01 -0800
"Tom Van Baak"  wrote:

> > How exactly do you measure offset of your GPS time output to
> > absolute UTC time?  
> 
> Conceptually it's no different from measuring your favorite resister
> or thermometer: you compare your DUT against a standard REF and the
> difference is your error, a process called calibration.

Yup, I worked in metrology for a while.  John Fluke Mfg Co., Inc.

> Calibrating your UTC is harder.

Yup.

> Here are couple examples:
> That's enough reading to keep you busy for a few days.

Yup, I will, thanks.  Now when was the last time you did that absolute
calibration of a GPS receiver to UTC?  Can we see the results?

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo Chris!

On Wed, 8 Nov 2017 11:47:05 -0600
"Chris Caudle"  wrote:

> On Wed, November 8, 2017 10:45 am, Gary E. Miller wrote:
> > No one here has yet bothered to address the issues I raise
> > in Section 3.3.4.  
> 
> Sure they did.  Why are you referencing the old version instead of the
> newer version that Leo Bodner provided the link to?

Because that was sent last night after I stopped reading email.

I knew about the errata, I left out that detail to see when someone
actually read my citation.  Leo actually did, but not got to his email
yet, I read email in reverse chrono order.

> https://www.gps.gov/technical/icwg/IRN-IS-200H-001+002+003_rollup.pdf

What I said is correct, IS-GPS-200H is STILL the latest version of
the GPS standard.  Leo's link, which I found Monday, is to a copy of
IS-GPS-200H with the errata applied.  So not technically an update to
IS-GPS-200H.

> "The NAV data contains the requisite data for relating GPS time to
> UTC. The accuracy of this data during the transmission interval shall
> be such that it relates GPS time (maintained by the MCS of the CS) to
> UTC (USNO) within 20 nanoseconds (one sigma). "

So yes, UTC from a GPS is now 20 ns (one sigama).  What I said about
+/- 13 ns being noise relative to the spec still applies.

Do you now see how measured GPS time/location can be very precise, but
UTC from a GPS less so?  Have you read the entire 3.3.4?

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Chris Caudle]

On Wed, November 8, 2017 10:45 am, Gary E. Miller wrote:
> No one here has yet bothered to address the issues I raise
> in Section 3.3.4.

Sure they did.  Why are you referencing the old version instead of the
newer version that Leo Bodner provided the link to?

https://www.gps.gov/technical/icwg/IRN-IS-200H-001+002+003_rollup.pdf

"The NAV data contains the requisite data for relating GPS time to UTC. 
The accuracy of this data during the transmission interval shall be such
that it relates GPS time (maintained by the MCS of the CS) to UTC (USNO)
within 20 nanoseconds (one sigma). "

-- 
Chris Caudle


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Tom Van Baak]

> How exactly do you measure offset of your GPS time output to absolute UTC 
> time?

Conceptually it's no different from measuring your favorite resister or 
thermometer: you compare your DUT against a standard REF and the difference is 
your error, a process called calibration. So the same is true for SI second 
(time interval, frequency) and UTC (time epoch). As I mentioned earlier, 
calibrating your SI second is quite simple. Calibrating your UTC is harder.

Here are couple examples:

(1) Years ago fellow time-nut Doug loaned out his and my antenna/receiver to be 
calibrated. The report will give you an idea of what's involved:

"Absolute Calibration of a Geodetic Time Transfer System"
http://xenon.colorado.edu/paperIrevise2.pdf


(2) Here's classic report from fellow time-nut Rick:

http://www.cnssys.com/files/PTTI/PTTI_2002_CNS_Testbed.pdf
and
http://www.cnssys.com/files/PTTI/Low_cost_GPS-based_time_and_frequency_products.pdf


(3) In both cases above there is transport of equipment involved. But the 
equipment can come to you instead:

http://www.usno.navy.mil/USNO/time/twstt/calibration-services
see also
http://tycho.usno.navy.mil/twstt.html
and a nice photo of the traveling time van:
http://tycho.usno.navy.mil/gif/2waytruck.jpg


(4) NIST also offers time & frequency calibration services:

https://www.nist.gov/calibrations/calibration-areas/time-and-frequency

"A NIST Disciplined Oscillator: Delivering UTC(NIST) to the Calibration 
Laboratory"
https://www.nist.gov/sites/default/files/documents/calibrations/NCSLI.pdf

"Remote Time Calibrations via the NIST Time Measurement and Analysis Service"
https://www.nist.gov/sites/default/files/documents/calibrations/Remote-Time-Calibrations.pdf

That's enough reading to keep you busy for a few days.

/tvb

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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo jimlux!

On Wed, 8 Nov 2017 06:33:19 -0800
jimlux  wrote:

> On 11/7/17 8:39 PM, Gary E. Miller wrote:
> > Yo Tom!
> > 
> > On Tue, 7 Nov 2017 20:16:09 -0800
> > "Tom Van Baak"  wrote:
> >   
> >>> Which is small compared to the published GPS time resolution
> >>> (IS_GPS_200H, page 54) of 90 ns.  
> >>
> >> Correct. GPS performs far better than the original spec. Like the
> >> Mars rovers...  
> > 
> > Of course, but then you are on a wing and a prayer, not
> > engineering.  
> 
> Not really - the original spec for GPS was based on being able to
> track to a single chip of the PN code at 1 MHz, or about 300m
> position error, and 30m for the precise code at 10MHz.

I agree with almost all you ssid.  And none of it applies to the point I
made.  I'm talking about the current GPS standard (IS-GPS-200H), nothing
dated at all.  No one here has yet bothered to address the issues I raise
in Section 3.3.4.  What I say about 3.3.4 is perfectly compatible with with
your arguments.

I'll be happy to discuss my interpretation of 3.3.4 and what I think it
means, when someone shows they actually read it.

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[jimlux]

On 11/7/17 8:39 PM, Gary E. Miller wrote:

Yo Tom!

On Tue, 7 Nov 2017 20:16:09 -0800
"Tom Van Baak"  wrote:


Which is small compared to the published GPS time resolution
(IS_GPS_200H, page 54) of 90 ns.


Correct. GPS performs far better than the original spec. Like the
Mars rovers...


Of course, but then you are on a wing and a prayer, not engineering.


Not really - the original spec for GPS was based on being able to track 
to a single chip of the PN code at 1 MHz, or about 300m position error, 
and 30m for the precise code at 10MHz.


And that was the limit of the technology back in the late 70s early 80s
A fancy multichannel correlator was literally a rack of equipment, and 
things like RAKE receivers to deal with multipath were the subject of 
papers in IEEE transactions - hardly a "buy it at the hardware store"


What has changed, and what's sort of amazing, given that the GPS signal 
hasn't really changed much is that technology has made substantial 
advances,  both in terms of silicon and in terms of the algorithms.


It is easy now to have a 64 simultaneous channel correlator that 
trivially tracks to a fraction of a chip and also recovers the carrier 
phase.  Codeless receivers allow tracking of the higher rate code, and 
today, a L1 only receiver is sort of a legacy oddity - perhaps because 
it has some peculiarity for a particular system, or a "drive every tenth 
of a penny out of the system cost" item.


Back in "30 m CEP" days who cared about the fact that the receive 
antenna phase center wasn't the same for all look angles.  Today, folks 
go out and extensively calibrate these things, and build antennas where 
the phase center is "stable" to 1 mm or better.



We've got much, much better analytical tools to process the data - folks 
regularly process long collections of data from inexpensive receivers 
where one has to account for things like solid earth tides, not to 
mention continental drift.  My house in Southern CA is steadily heading 
north a few cm/year. That's actually measureable with equipment you 
could reasonably buy for under $1000 (I think.. you might be able to do 
it for under $100)



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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Leo Bodnar]

> Subject: Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

I have not read IS-GPS for quite awhile so out of curiosity found what I 
believe is the latest one 
https://www.gps.gov/technical/icwg/IRN-IS-200H-001+002+003_rollup.pdf

It states "The OCS shall control the GPS time scale to be within one 
microsecond of UTC (modulo one second).
The NAV data contains the requisite data for relating GPS time to UTC. The 
accuracy of this data during the transmission interval shall be such that it 
relates GPS time (maintained by the MCS of the CS) to UTC (USNO) within 20 
nanoseconds (one sigma)."

My understanding is:  the target difference between UTC and GPS time TOS is 1µs 
or less.  This is just an operational target and does not affect conversion 
accuracy.
The end user is provided required GPS to UTC correction data - in legacy NAV 
and [reasonably] new CNAV messages to perform conversion locally with expected 
accuracy to below 20ns (1 sigma.)
Time conversion accuracy is further diluted by uncertainty of GPS time itself - 
by design (accuracy of data in ephemeris), by receiver implementation 
(correlator resolution, etc) and environment (ionospheric disturbances, 
multipath, etc.)

GPS to UTC correction data contains constant offset and its rate of change for 
LNAV messages and adds extra 2nd order correction (rate of rate of change) for 
CNAV messages.

Leo
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Ole Petter Ronningen]

Hi, Jim!

On Wed, Nov 8, 2017 at 3:12 AM, jimlux  wrote:

>
> http://www.navipedia.net/index.php/Ionospheric_Delay
> has a nice discussion with simple equations to turn TEC into delay, etc.
>

I've already skimmed this, and it requires a bit more brainpower than I can
muster for what I want to accomplish.. :) BUT! Re-reading it I got to the
page on "Combination of GNSS Measurements" - and the geometry free
combination of L1 and L2 is exactly what I was looking for; some quantity
proportional to TEC that I can correlate with the daily excursions of the
Ublox PPS. So, yeah, thanks! That gave me just what I needed! :) Now to
cobble up a RINEX parser..


> You might also look into seeing if you can put your data in a form to be
> processed by GIPSY at JPL - they have a service where you can upload your
> raw observables and they post process it.
>

GIPSY solves using PPP, does it not? I already process the data with PPP
from each of the receivers using both the  NRCan online service and locally
using gLAB - using one to "sanity check" the results from the other, but
I'll have another look at GIPSY.

Thanks!
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Tim Lister]

On Tue, Nov 7, 2017 at 8:39 PM, Gary E. Miller  wrote:
> Yo Tom!
>
> On Tue, 7 Nov 2017 20:16:09 -0800
> "Tom Van Baak"  wrote:
>
>> > Which is small compared to the published GPS time resolution
>> > (IS_GPS_200H, page 54) of 90 ns.
>>
>> Correct. GPS performs far better than the original spec. Like the
>> Mars rovers...
>
> Of course, but then you are on a wing and a prayer, not engineering.
>
>> As a result we're now all used to ~10 ns level of performance out of
>> GPS, even in a $5 receiver.
>
> I'm sure we are not talking about the same thing here.  Your talking
> about GPS time?  I'm talking about UTC as output from a GPS, after it
> converted from GPS time.
>
>
> I am NOT talking about the 'performance' of GPS. What is performance?
> We talking about frequency stability, or position accuracy, or we
> talking about absolute offset from USNO UTC time?  I'm talking about
> the later. I'm talking about the spec about how close the GPS time is
> to UTC time. Your GPS converts the GPS time to UTC time depending on an
> ephemeris parameter that the GPS owners say is 90 ns (one sigma).
>
> Sure, you may get better, but when you are looking at subtle error sources
> that is surely one to look at.
>
> How exactly do you measure offset of your GPS time output to absolute
> UTC time?

That was what Tom's attached plot was showing: the measured difference
from GPS system time distributed through the satellites to UTC realized
at USNO "UTC(USNO)". This is also available (only in arrears) through
the BIPM's Circular T which also give the differences 'UTC-UTC(USNO)'.
With these two sets of offsets and some interpolation (you only get values
every 5 days in the Circular T) you can back-track from GPS time to
"true" UTC but only about 1 month after the observations.

>
>> Closer to ~1 ns is possible when you dig
>> into the bag-of-timing-tricks like zero-D mode, sawtooth correction,
>> antenna calibration, multi-path mitigating antennae, dual-frequency
>> receivers, external frequency references, post-processing,
>> temperature stabilization of antenna, cables, receiver, etc.
>
> Yes, of course, but NONE of that fixes the GPS to UTC offset problem.
> It makes the GPS time much better, but does not solve the problem that
> the GPS to UTC offset is only good to 90 ns (one sigma).  Is your GPS
> getting a better offset correction somewhere else?  Otherwis it has NO
> way to compute/calculate/devine that offset.
>

I've not read the spec, but presumably there must be a way to get better
accuracy and/or the system is being operated and kept to tighter tolerances
than the original written spec otherwise the quoted measured offsets between
GPS time and UTC(USNO), which are quoted in the Circular T to 0.1ns if
I remember right, would be vast overkill.

>
>> So the
>> industry big boys are getting sub-cm levels of positioning and sub-ns
>> levels of timing. It's all pretty cool. Some time nuts are not far
>> behind.
>
> I have seen cm level precision myself.  But that is unrelated to the issue
> I bring up.  The positioning depends on stable GPS time, and I agree GPS
> time is much more stable than 90 ns.  I thought the subject was UTC offsets.
>
>> Note also that relative timing, such as needed by a GPSDO frequency
>> standard is always much better than absolute timing, such as needed
>> by a UTC time standard. This is because many of the unknown offsets
>> (antenna, cable, receiver RF and f/w) magically cancel when used as a
>> GPSDO. This is why some GPSDO can get down to parts in 10^14th
>> frequency stability over a day.
>
> Yes, I 100% agree, and totally unrelated to my point.  Frequency stability
> is only loosely correlated to absolute time accuracy.  Stable !=
> accurate.
>
>> There's a slide I remember seeing that shows how GPS timing accuracy
>> has improved since the early days. It's page 9 (attached) of:
>
> I agree, GPS accuracy is great, but I am NOT talking about GPS timing,
> I am talking about UTC timing accuracy.
>
> I thought the problem was that the UTC time from the GPS was wandering
> on a diurnal time frame.  The GPS can be perfect to one hundred 9s,
> the GPS position can be perfect to 100 nines, but if the transmitted
> GPS time to UTC time offset is said, by the US Military, to be only 90
> ns (one sigma), then I'd listen to them when it matters.
>
> Time for us all to actually read the standard and argue what that means.
>
> RGDS
> GARY


Cheers,
Tim
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo Tom!

On Tue, 7 Nov 2017 20:16:09 -0800
"Tom Van Baak"  wrote:

> > Which is small compared to the published GPS time resolution
> > (IS_GPS_200H, page 54) of 90 ns.  
> 
> Correct. GPS performs far better than the original spec. Like the
> Mars rovers...

Of course, but then you are on a wing and a prayer, not engineering.

> As a result we're now all used to ~10 ns level of performance out of
> GPS, even in a $5 receiver.

I'm sure we are not talking about the same thing here.  Your talking
about GPS time?  I'm talking about UTC as output from a GPS, after it
converted from GPS time.


I am NOT talking about the 'performance' of GPS. What is performance?
We talking about frequency stability, or position accuracy, or we
talking about absolute offset from USNO UTC time?  I'm talking about
the later. I'm talking about the spec about how close the GPS time is
to UTC time. Your GPS converts the GPS time to UTC time depending on an
ephemeris parameter that the GPS owners say is 90 ns (one sigma).

Sure, you may get better, but when you are looking at subtle error sources
that is surely one to look at.

How exactly do you measure offset of your GPS time output to absolute
UTC time?

> Closer to ~1 ns is possible when you dig
> into the bag-of-timing-tricks like zero-D mode, sawtooth correction,
> antenna calibration, multi-path mitigating antennae, dual-frequency
> receivers, external frequency references, post-processing,
> temperature stabilization of antenna, cables, receiver, etc.

Yes, of course, but NONE of that fixes the GPS to UTC offset problem.
It makes the GPS time much better, but does not solve the problem that
the GPS to UTC offset is only good to 90 ns (one sigma).  Is your GPS
getting a better offset correction somewhere else?  Otherwis it has NO
way to compute/calculate/devine that offset.


> So the
> industry big boys are getting sub-cm levels of positioning and sub-ns
> levels of timing. It's all pretty cool. Some time nuts are not far
> behind.

I have seen cm level precision myself.  But that is unrelated to the issue
I bring up.  The positioning depends on stable GPS time, and I agree GPS
time is much more stable than 90 ns.  I thought the subject was UTC offsets.

> Note also that relative timing, such as needed by a GPSDO frequency
> standard is always much better than absolute timing, such as needed
> by a UTC time standard. This is because many of the unknown offsets
> (antenna, cable, receiver RF and f/w) magically cancel when used as a
> GPSDO. This is why some GPSDO can get down to parts in 10^14th
> frequency stability over a day.

Yes, I 100% agree, and totally unrelated to my point.  Frequency stability
is only loosely correlated to absolute time accuracy.  Stable !=
accurate.

> There's a slide I remember seeing that shows how GPS timing accuracy
> has improved since the early days. It's page 9 (attached) of:

I agree, GPS accuracy is great, but I am NOT talking about GPS timing,
I am talking about UTC timing accuracy.

I thought the problem was that the UTC time from the GPS was wandering
on a diurnal time frame.  The GPS can be perfect to one hundred 9s,
the GPS position can be perfect to 100 nines, but if the transmitted
GPS time to UTC time offset is said, by the US Military, to be only 90
ns (one sigma), then I'd listen to them when it matters.

Time for us all to actually read the standard and argue what that means.

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[jimlux]

On 11/7/17 1:44 PM, MLewis wrote:

Yo Gary!

With a strictly SSE skyview, I still regularly get signals from sats to 
my NW. When they're at the right elevation and heading, their signals 
pass over me and reflect back at me from a tall building. When running 
my M8T with the position unlocked, and those NW sats are getting a 
reflection and reporting in, (although the reflecting building is 
further away to the SE) my GPS position drifts up to 300' to my south (S 
of SSE). (reported position goes for a walk, staggering across the 
parking lot, wanders through a park with an occasional loop, across a 
road, then sits down for a while, before wandering back)


Is it reasonable to use the 9" ~= 1 ns for:
running with a fixed & correct survey position, and NW sats reflecting a 
signal to me, that 300' drift would equate to a (300' x 12") /  9" = 
400, for a ballpark 400 ns error?




No.. in free space it's about a foot per nanosecond.. 9" is 0.75 
velocity factor, reasonable for coax, for instance, depending on the 
dielectric.





Thanks,

Michael

On 07/11/2017 3:40 PM, Gary E. Miller wrote:

Yo Lars!

On Tue, 7 Nov 2017 20:32:19 +
Lars Walenius  wrote:


Another question: If You have an error in the surveyed position of
say 3meters and you receive all of the available satellites in all
directions how much will this really affect your timing?

I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway.
When asked, she handed out 9 inch long peieces of wire, and said: that
is a nanaosecond.

3m is about 118.11 inches is about 13 ns.  So worst case, skipping the
3D math, yoy get about +/13 ns.

Which is small compared to the published GPS time resolution 
(IS_GPS_200H,

page 54) of 90 ns.

RGDS
GARY
--- 


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

    Veritas liberabit vos. -- Quid est veritas?
 "If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[jimlux]

On 11/7/17 1:30 PM, Ole Petter Ronningen wrote:

Not knowing better, I would expect there to be diurnal effects due to the
ionospere being in the shade or not. I suspect there are people on this
list that know better.

Anyway, the effect I am seeing is also very slowly drifing, see screenshot
of about 20 days of data below. The daily variation varies quite a bit. I
am not sure this can be explained by ionospheric activity, but then again I
dont know much about what goes on up there.

As mentioned, I also have L1/L2 data from the same period, I believe it is
possible to extract or at least estimate the Total Electron Content from
that data somehow, but I do not know how - it gets pretty arcane pretty
quickly for a layman.

Ole



http://www.navipedia.net/index.php/Ionospheric_Delay
has a nice discussion with simple equations to turn TEC into delay, etc.


You might also look into seeing if you can put your data in a form to be 
processed by GIPSY at JPL - they have a service where you can upload 
your raw observables and they post process it.


https://gipsy-oasis.jpl.nasa.gov/



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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo MLewis!

On Tue, 7 Nov 2017 16:44:05 -0500
MLewis  wrote:

> With a strictly SSE skyview, I still regularly get signals from sats
> to my NW. When they're at the right elevation and heading, their
> signals pass over me and reflect back at me from a tall building.
> When running my M8T with the position unlocked, and those NW sats are
> getting a reflection and reporting in, (although the reflecting
> building is further away to the SE) my GPS position drifts up to 300'
> to my south (S of SSE). (reported position goes for a walk,
> staggering across the parking lot, wanders through a park with an
> occasional loop, across a road, then sits down for a while, before
> wandering back)

Yeah, one of my test locations has similar issues.  It leads to some
'interesting' results.

> Is it reasonable to use the 9" ~= 1 ns for:
> running with a fixed & correct survey position, and NW sats
> reflecting a signal to me, that 300' drift would equate to a (300' x
> 12") /  9" = 400, for a ballpark 400 ns error?

I think it is reasonable as a worst case.  Basically a 1D model of a
3D problem.  With good sat angles, the 3m location change will be
trigonomically smaller for a sat at an angle.

But, as I said, given that GPS only resolves to 90 ns, the worst case
+/- 13 ns is noise.

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Leo Bodnar]

Coincidentally, I have been testing relative phase difference of two GPS clocks 
http://www.leobodnar.com/shop/index.php?main_page=product_info=107_id=301
 since Friday. 
They are completely independent, including separate antennas and positioned a 
few yards away from each other so ionospheric disturbances would affect both 
units equally.  Devices use Ublox chipset.

Average phase difference did not change in four days since Friday but there is 
phase wander within around 10ns.
Here is a video of 4 hours worth of data.  One horizontal division is 20ns:

http://leobodnar.com/balloons/NTP/twoGPSclocks.mp4

Cheers
Leo 

> From: Lars Walenius 
> If I look on the NIST database for the last days it seems to be a daily 
> variation of about 8-10ns. Could this be for the same reason as Ole’s 
> variation? Is the daily variations due to not perfect ionosphere correction? 
> Can you get much better than the data in the NIST database for an ordinary 
> timing receiver like the LEA-6T?


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Chris Caudle]

On Tue, November 7, 2017 3:30 pm, Ole Petter Ronningen wrote:
> Not knowing better, I would expect there to be diurnal effects due to the
> ionospere being in the shade or not.

I think that is generally true.

> Anyway, the effect I am seeing is also very slowly drifting, see screenshot
> of about 20 days of data below.

Your pictures are not making it to the list, it seems the list server
strips out inline images.  Actually inline images would imply you are
probably sending HTML messages and they are getting converted to plain
text.  You could try attaching the image as an attachment to a plain text
message, that may get through to the list.

Regarding the drifting, if you mean relative to the wall clock time, GPS
to planet alignment shifts because of rotation of earth, so the GPS
effects tend to align to around 23 hours, not 24 hours.  Is that the drift
you are seeing, or more than about an hour per day relative to solar time?

-- 
Chris Caudle


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[MLewis]

Yo Gary!

With a strictly SSE skyview, I still regularly get signals from sats to 
my NW. When they're at the right elevation and heading, their signals 
pass over me and reflect back at me from a tall building. When running 
my M8T with the position unlocked, and those NW sats are getting a 
reflection and reporting in, (although the reflecting building is 
further away to the SE) my GPS position drifts up to 300' to my south (S 
of SSE). (reported position goes for a walk, staggering across the 
parking lot, wanders through a park with an occasional loop, across a 
road, then sits down for a while, before wandering back)


Is it reasonable to use the 9" ~= 1 ns for:
running with a fixed & correct survey position, and NW sats reflecting a 
signal to me, that 300' drift would equate to a (300' x 12") /  9" = 
400, for a ballpark 400 ns error?


Thanks,

Michael

On 07/11/2017 3:40 PM, Gary E. Miller wrote:

Yo Lars!

On Tue, 7 Nov 2017 20:32:19 +
Lars Walenius  wrote:


Another question: If You have an error in the surveyed position of
say 3meters and you receive all of the available satellites in all
directions how much will this really affect your timing?

I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway.
When asked, she handed out 9 inch long peieces of wire, and said: that
is a nanaosecond.

3m is about 118.11 inches is about 13 ns.  So worst case, skipping the
3D math, yoy get about +/13 ns.

Which is small compared to the published GPS time resolution (IS_GPS_200H,
page 54) of 90 ns.

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

Veritas liberabit vos. -- Quid est veritas?
 "If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo Lars!

On Tue, 7 Nov 2017 20:32:19 +
Lars Walenius  wrote:

> Another question: If You have an error in the surveyed position of
> say 3meters and you receive all of the available satellites in all
> directions how much will this really affect your timing?

I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway.
When asked, she handed out 9 inch long peieces of wire, and said: that
is a nanaosecond.

3m is about 118.11 inches is about 13 ns.  So worst case, skipping the
3D math, yoy get about +/13 ns.

Which is small compared to the published GPS time resolution (IS_GPS_200H,
page 54) of 90 ns.

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Lars Walenius]

Hi all,



If I look on the NIST database for the last days it seems to be a daily 
variation of about 8-10ns. Could this be for the same reason as Ole’s 
variation? Is the daily variations due to not perfect ionosphere correction? 
Can you get much better than the data in the NIST database for an ordinary 
timing receiver like the LEA-6T?



https://www.nist.gov/pml/time-and-frequency-division/services/gps-data-archive



Another question: If You have an error in the surveyed position of say 3meters 
and you receive all of the available satellites in all directions how much will 
this really affect your timing?



Sorry for all the silly questions.



Lars






Från: time-nuts <time-nuts-boun...@febo.com> för Bob Camp <kb...@n1k.org>
Skickat: Tuesday, November 7, 2017 8:21:44 PM
Till: Discussion of precise time and frequency measurement
Ämne: Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

Hi

If you go back into the NIST evaluations of various receiver modules ….. they 
don’t always
work best with the correct coordinates. Some have guessed there are residual 
math errors
in the devices. Others suggest the “radio side” may be at fault.  Indeed 
varying susceptibility
to multipath *might* be the answer.

Bob

> On Nov 7, 2017, at 2:12 PM, Ole Petter Ronningen <opronnin...@gmail.com> 
> wrote:
>
> Yes, I thought so too - but on the same antenna I have a couple of L1/L2
> continously logging survey receivers; the position accuracy should be
> within 5-10 mm. Unless I've messed something up with coordinate systems,
> the position the UBlox thinks it has should be pretty good.
>
> Ole
>
> On Tue, Nov 7, 2017 at 5:43 PM, Jean-Louis Oneto <jl.on...@free.fr> wrote:
>
>> Hi Ole,
>> I think that the long term undulation are caused by a (small) error in
>> geodetic position of the antenna. The period should be a sidereal day
>> (23:56...)
>> Have a good day,
>> Jean-Louis
>>
>>
>>
>> Envoyé depuis mon appareil mobile Samsung.
>>
>>  Message d'origine 
>> De : Ole Petter Ronningen <opronnin...@gmail.com>
>> Date :07/11/2017  15:15  (GMT+01:00)
>> A : Discussion of precise time and frequency measurement <
>> time-nuts@febo.com>
>> Objet : Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
>>
>> Hi all
>>
>> Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen
>> maser. From 00:00 the bare receiver board was inside a polystyrene box
>> where it has soaked for many months, at 16:00 I removed the box exposing
>> the board to the airflow in the room, including AC. The box was left off
>> for the rest of the day.
>>
>> The green trace is temperature in the lab. The "long term undulation" in
>> phase is normal, although I do not know the precise cause (multipath or
>> something else. I am reasonably sure it is not related to temperature in
>> the lab.
>>
>> [image: Inline image 1])
>>
>> Ole
>>
>> On Sat, Nov 4, 2017 at 6:06 PM, Denny Page <de...@cococafe.com> wrote:
>>
>>> [I hate finding unsent email in my folder :-]
>>>
>>> Others may disagree, but I doubt that the type of small temperature
>>> variation you are referring to has any meaningful effect on tracking.
>> While
>>> the datasheet for the M8T says that there can be "significant impact" to
>>> the specifications at “extreme operating temperatures,” it gives the
>>> operating temperature as -40 to +85 C. Simply said, if you can stand to
>> be
>>> in the same room/space with it, I think you are fine.
>>>
>>> Of much greater interest would be the antenna and it’s placement. I’m
>>> afraid I can’t specifically recommend a “good” antenna, but perhaps
>> others
>>> on the list can. For my EVK-M8T, I’m using the antenna that came with the
>>> kit and it works very well. I haven’t tested other antennas with the M8T
>> at
>>> this time, but I do have a number of other devices with antennas that
>> work
>>> well. I also have a few antennas that work poorly with all the devices,
>>> including the ones with which they came. Unfortunately pretty much all of
>>> them lack sufficient identification markings to identify
>> manufacture/model
>>> info.
>>>
>>> Regarding placement, I’ve found that in a restricted area even a few
>>> inches can have a significant impact on the average number of satellites
>>> and signal level. In my case, it’s associated with the single building
>>> structure, but it sounds your case is even more re

Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Bob Camp]

Hi

If you go back into the NIST evaluations of various receiver modules ….. they 
don’t always
work best with the correct coordinates. Some have guessed there are residual 
math errors
in the devices. Others suggest the “radio side” may be at fault.  Indeed 
varying susceptibility 
to multipath *might* be the answer.

Bob

> On Nov 7, 2017, at 2:12 PM, Ole Petter Ronningen <opronnin...@gmail.com> 
> wrote:
> 
> Yes, I thought so too - but on the same antenna I have a couple of L1/L2
> continously logging survey receivers; the position accuracy should be
> within 5-10 mm. Unless I've messed something up with coordinate systems,
> the position the UBlox thinks it has should be pretty good.
> 
> Ole
> 
> On Tue, Nov 7, 2017 at 5:43 PM, Jean-Louis Oneto <jl.on...@free.fr> wrote:
> 
>> Hi Ole,
>> I think that the long term undulation are caused by a (small) error in
>> geodetic position of the antenna. The period should be a sidereal day
>> (23:56...)
>> Have a good day,
>> Jean-Louis
>> 
>> 
>> 
>> Envoyé depuis mon appareil mobile Samsung.
>> 
>>  Message d'origine 
>> De : Ole Petter Ronningen <opronnin...@gmail.com>
>> Date :07/11/2017  15:15  (GMT+01:00)
>> A : Discussion of precise time and frequency measurement <
>> time-nuts@febo.com>
>> Objet : Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
>> 
>> Hi all
>> 
>> Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen
>> maser. From 00:00 the bare receiver board was inside a polystyrene box
>> where it has soaked for many months, at 16:00 I removed the box exposing
>> the board to the airflow in the room, including AC. The box was left off
>> for the rest of the day.
>> 
>> The green trace is temperature in the lab. The "long term undulation" in
>> phase is normal, although I do not know the precise cause (multipath or
>> something else. I am reasonably sure it is not related to temperature in
>> the lab.
>> 
>> [image: Inline image 1])
>> 
>> Ole
>> 
>> On Sat, Nov 4, 2017 at 6:06 PM, Denny Page <de...@cococafe.com> wrote:
>> 
>>> [I hate finding unsent email in my folder :-]
>>> 
>>> Others may disagree, but I doubt that the type of small temperature
>>> variation you are referring to has any meaningful effect on tracking.
>> While
>>> the datasheet for the M8T says that there can be "significant impact" to
>>> the specifications at “extreme operating temperatures,” it gives the
>>> operating temperature as -40 to +85 C. Simply said, if you can stand to
>> be
>>> in the same room/space with it, I think you are fine.
>>> 
>>> Of much greater interest would be the antenna and it’s placement. I’m
>>> afraid I can’t specifically recommend a “good” antenna, but perhaps
>> others
>>> on the list can. For my EVK-M8T, I’m using the antenna that came with the
>>> kit and it works very well. I haven’t tested other antennas with the M8T
>> at
>>> this time, but I do have a number of other devices with antennas that
>> work
>>> well. I also have a few antennas that work poorly with all the devices,
>>> including the ones with which they came. Unfortunately pretty much all of
>>> them lack sufficient identification markings to identify
>> manufacture/model
>>> info.
>>> 
>>> Regarding placement, I’ve found that in a restricted area even a few
>>> inches can have a significant impact on the average number of satellites
>>> and signal level. In my case, it’s associated with the single building
>>> structure, but it sounds your case is even more restrictive. Although it
>>> can be a very lengthy process, performing antenna surveys may help
>> improve
>>> your situation. For each location, you need to monitor the number of
>>> satellites and signal level for 24 hours or more before determining the
>>> relative merit of that location. Repeat… and repeat.. and repeat.
>>> Determining the very best location for the antenna will likely require as
>>> many antenna surveys as you have patience for. :)
>>> 
>>> Hope this helps.
>>> 
>>> Denny
>>> 
>>> 
>>>> On Nov 02, 2017, at 18:54, MLewis <mlewis...@rogers.com> wrote:
>>>> 
>>>> Earlier this week, I put the breakout board with my NEO-M8T into an
>>> aluminum can. The can is split into a lower half and an upper half. The
>>> lower half was insulated on its side

Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Ole Petter Ronningen]

Yes, I thought so too - but on the same antenna I have a couple of L1/L2
continously logging survey receivers; the position accuracy should be
within 5-10 mm. Unless I've messed something up with coordinate systems,
the position the UBlox thinks it has should be pretty good.

Ole

On Tue, Nov 7, 2017 at 5:43 PM, Jean-Louis Oneto <jl.on...@free.fr> wrote:

> Hi Ole,
> I think that the long term undulation are caused by a (small) error in
> geodetic position of the antenna. The period should be a sidereal day
> (23:56...)
> Have a good day,
> Jean-Louis
>
>
>
> Envoyé depuis mon appareil mobile Samsung.
>
>  Message d'origine 
> De : Ole Petter Ronningen <opronnin...@gmail.com>
> Date :07/11/2017  15:15  (GMT+01:00)
> A : Discussion of precise time and frequency measurement <
> time-nuts@febo.com>
> Objet : Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
>
> Hi all
>
> Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen
> maser. From 00:00 the bare receiver board was inside a polystyrene box
> where it has soaked for many months, at 16:00 I removed the box exposing
> the board to the airflow in the room, including AC. The box was left off
> for the rest of the day.
>
> The green trace is temperature in the lab. The "long term undulation" in
> phase is normal, although I do not know the precise cause (multipath or
> something else. I am reasonably sure it is not related to temperature in
> the lab.
>
> [image: Inline image 1])
>
> Ole
>
> On Sat, Nov 4, 2017 at 6:06 PM, Denny Page <de...@cococafe.com> wrote:
>
> > [I hate finding unsent email in my folder :-]
> >
> > Others may disagree, but I doubt that the type of small temperature
> > variation you are referring to has any meaningful effect on tracking.
> While
> > the datasheet for the M8T says that there can be "significant impact" to
> > the specifications at “extreme operating temperatures,” it gives the
> > operating temperature as -40 to +85 C. Simply said, if you can stand to
> be
> > in the same room/space with it, I think you are fine.
> >
> > Of much greater interest would be the antenna and it’s placement. I’m
> > afraid I can’t specifically recommend a “good” antenna, but perhaps
> others
> > on the list can. For my EVK-M8T, I’m using the antenna that came with the
> > kit and it works very well. I haven’t tested other antennas with the M8T
> at
> > this time, but I do have a number of other devices with antennas that
> work
> > well. I also have a few antennas that work poorly with all the devices,
> > including the ones with which they came. Unfortunately pretty much all of
> > them lack sufficient identification markings to identify
> manufacture/model
> > info.
> >
> > Regarding placement, I’ve found that in a restricted area even a few
> > inches can have a significant impact on the average number of satellites
> > and signal level. In my case, it’s associated with the single building
> > structure, but it sounds your case is even more restrictive. Although it
> > can be a very lengthy process, performing antenna surveys may help
> improve
> > your situation. For each location, you need to monitor the number of
> > satellites and signal level for 24 hours or more before determining the
> > relative merit of that location. Repeat… and repeat.. and repeat.
> > Determining the very best location for the antenna will likely require as
> > many antenna surveys as you have patience for. :)
> >
> > Hope this helps.
> >
> > Denny
> >
> >
> > > On Nov 02, 2017, at 18:54, MLewis <mlewis...@rogers.com> wrote:
> > >
> > > Earlier this week, I put the breakout board with my NEO-M8T into an
> > aluminum can. The can is split into a lower half and an upper half. The
> > lower half was insulated on its sides internally, but open to the upper
> > half, which wasn't insulated. The lower area contains the NEO-M8T on its
> > breakout board and its matching com breakout board.
> > >
> > > In the unusual skyview/RF environment described below:
> > > - LH was typically showing two or three green sats, with a min of none
> > and a max of five for very brief periods.
> > > - The average dBc of the green sats was 22 dBc, with a max of 29 dBc.
> > > - Two screen shots of LH from this time period show an Accu of 12 ns
> and
> > 33 ns.
> > >
> > > This morning, I insulated the inside of the upper half of the can, and
> > added insulation to seal the top of the lower area into a chamber that
> &

Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Jean-Louis Oneto]

Hi Ole,
I think that the long term undulation are caused by a (small) error in geodetic 
position of the antenna. The period should be a sidereal day (23:56...)
Have a good day, 
Jean-Louis 



Envoyé depuis mon appareil mobile Samsung.

 Message d'origine 
De : Ole Petter Ronningen <opronnin...@gmail.com> 
Date :07/11/2017  15:15  (GMT+01:00) 
A : Discussion of precise time and frequency measurement <time-nuts@febo.com> 
Objet : Re: [time-nuts] ublox NEO-M8T improved by insulated chamber? 

Hi all

Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen
maser. From 00:00 the bare receiver board was inside a polystyrene box
where it has soaked for many months, at 16:00 I removed the box exposing
the board to the airflow in the room, including AC. The box was left off
for the rest of the day.

The green trace is temperature in the lab. The "long term undulation" in
phase is normal, although I do not know the precise cause (multipath or
something else. I am reasonably sure it is not related to temperature in
the lab.

[image: Inline image 1])

Ole

On Sat, Nov 4, 2017 at 6:06 PM, Denny Page <de...@cococafe.com> wrote:

> [I hate finding unsent email in my folder :-]
>
> Others may disagree, but I doubt that the type of small temperature
> variation you are referring to has any meaningful effect on tracking. While
> the datasheet for the M8T says that there can be "significant impact" to
> the specifications at “extreme operating temperatures,” it gives the
> operating temperature as -40 to +85 C. Simply said, if you can stand to be
> in the same room/space with it, I think you are fine.
>
> Of much greater interest would be the antenna and it’s placement. I’m
> afraid I can’t specifically recommend a “good” antenna, but perhaps others
> on the list can. For my EVK-M8T, I’m using the antenna that came with the
> kit and it works very well. I haven’t tested other antennas with the M8T at
> this time, but I do have a number of other devices with antennas that work
> well. I also have a few antennas that work poorly with all the devices,
> including the ones with which they came. Unfortunately pretty much all of
> them lack sufficient identification markings to identify manufacture/model
> info.
>
> Regarding placement, I’ve found that in a restricted area even a few
> inches can have a significant impact on the average number of satellites
> and signal level. In my case, it’s associated with the single building
> structure, but it sounds your case is even more restrictive. Although it
> can be a very lengthy process, performing antenna surveys may help improve
> your situation. For each location, you need to monitor the number of
> satellites and signal level for 24 hours or more before determining the
> relative merit of that location. Repeat… and repeat.. and repeat.
> Determining the very best location for the antenna will likely require as
> many antenna surveys as you have patience for. :)
>
> Hope this helps.
>
> Denny
>
>
> > On Nov 02, 2017, at 18:54, MLewis <mlewis...@rogers.com> wrote:
> >
> > Earlier this week, I put the breakout board with my NEO-M8T into an
> aluminum can. The can is split into a lower half and an upper half. The
> lower half was insulated on its sides internally, but open to the upper
> half, which wasn't insulated. The lower area contains the NEO-M8T on its
> breakout board and its matching com breakout board.
> >
> > In the unusual skyview/RF environment described below:
> > - LH was typically showing two or three green sats, with a min of none
> and a max of five for very brief periods.
> > - The average dBc of the green sats was 22 dBc, with a max of 29 dBc.
> > - Two screen shots of LH from this time period show an Accu of 12 ns and
> 33 ns.
> >
> > This morning, I insulated the inside of the upper half of the can, and
> added insulation to seal the top of the lower area into a chamber that
> contained the GPS module board & its com board. Since then, its run for
> around ten hours, same weather as yesterday except more rain, ambient room
> temperature wasn't measured but is definitely warmer. Since after around an
> hour of running:
> > - LH has been showing between two and eight green sats, typically three
> to five:
> > - Their average dBc is 30 dBc, with a max of 37 dBc.
> > - LH Accu is showing as 6 ns.
> >
> > I have no idea what the temperature is inside the chamber.
> >
> > As I write this, LH is showing three green sats, at 33, 34 and 35 dBc.
> >
> > I expected a more stable internal TCXO in the GPS module, but I didn't
> expect stronger signals. Although perhaps I should have, as the block
> diagram for the NEO-M8T does show

Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Ole Petter Ronningen]

Hi all

Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen
maser. From 00:00 the bare receiver board was inside a polystyrene box
where it has soaked for many months, at 16:00 I removed the box exposing
the board to the airflow in the room, including AC. The box was left off
for the rest of the day.

The green trace is temperature in the lab. The "long term undulation" in
phase is normal, although I do not know the precise cause (multipath or
something else. I am reasonably sure it is not related to temperature in
the lab.

[image: Inline image 1])

Ole

On Sat, Nov 4, 2017 at 6:06 PM, Denny Page  wrote:

> [I hate finding unsent email in my folder :-]
>
> Others may disagree, but I doubt that the type of small temperature
> variation you are referring to has any meaningful effect on tracking. While
> the datasheet for the M8T says that there can be "significant impact" to
> the specifications at “extreme operating temperatures,” it gives the
> operating temperature as -40 to +85 C. Simply said, if you can stand to be
> in the same room/space with it, I think you are fine.
>
> Of much greater interest would be the antenna and it’s placement. I’m
> afraid I can’t specifically recommend a “good” antenna, but perhaps others
> on the list can. For my EVK-M8T, I’m using the antenna that came with the
> kit and it works very well. I haven’t tested other antennas with the M8T at
> this time, but I do have a number of other devices with antennas that work
> well. I also have a few antennas that work poorly with all the devices,
> including the ones with which they came. Unfortunately pretty much all of
> them lack sufficient identification markings to identify manufacture/model
> info.
>
> Regarding placement, I’ve found that in a restricted area even a few
> inches can have a significant impact on the average number of satellites
> and signal level. In my case, it’s associated with the single building
> structure, but it sounds your case is even more restrictive. Although it
> can be a very lengthy process, performing antenna surveys may help improve
> your situation. For each location, you need to monitor the number of
> satellites and signal level for 24 hours or more before determining the
> relative merit of that location. Repeat… and repeat.. and repeat.
> Determining the very best location for the antenna will likely require as
> many antenna surveys as you have patience for. :)
>
> Hope this helps.
>
> Denny
>
>
> > On Nov 02, 2017, at 18:54, MLewis  wrote:
> >
> > Earlier this week, I put the breakout board with my NEO-M8T into an
> aluminum can. The can is split into a lower half and an upper half. The
> lower half was insulated on its sides internally, but open to the upper
> half, which wasn't insulated. The lower area contains the NEO-M8T on its
> breakout board and its matching com breakout board.
> >
> > In the unusual skyview/RF environment described below:
> > - LH was typically showing two or three green sats, with a min of none
> and a max of five for very brief periods.
> > - The average dBc of the green sats was 22 dBc, with a max of 29 dBc.
> > - Two screen shots of LH from this time period show an Accu of 12 ns and
> 33 ns.
> >
> > This morning, I insulated the inside of the upper half of the can, and
> added insulation to seal the top of the lower area into a chamber that
> contained the GPS module board & its com board. Since then, its run for
> around ten hours, same weather as yesterday except more rain, ambient room
> temperature wasn't measured but is definitely warmer. Since after around an
> hour of running:
> > - LH has been showing between two and eight green sats, typically three
> to five:
> > - Their average dBc is 30 dBc, with a max of 37 dBc.
> > - LH Accu is showing as 6 ns.
> >
> > I have no idea what the temperature is inside the chamber.
> >
> > As I write this, LH is showing three green sats, at 33, 34 and 35 dBc.
> >
> > I expected a more stable internal TCXO in the GPS module, but I didn't
> expect stronger signals. Although perhaps I should have, as the block
> diagram for the NEO-M8T does show its TCXO pointing at a "Fractional N
> Synthesizer" inside the UBX-M8030's "RF Block". It also shows a RTC Crystal
> for a RTC inside the "Digital Block".
> >
> > Is this coincidence or can reception improve with:
> > - a higher temperature module?
> > - a more stable module temperature?
> >
> > I'm tempted to add some thermal mass (block of Al) to the top of the M8T
> and a chunk of insulation on top of that.
> >
> > Michael
> >
> > p.s.
> > As I finish this, LH is showing five sats, 23, 30, 31, 32 & 34 dBc, Accu
> 6 ns
> >
> > On 01/11/2017 9:55 AM, MLewis wrote:
> >> I had anticipated reception issues, which is why I went with the M8T
> for its sensitivity, multi-constellation and it's a timing module so a good
> PPS on a single sat - only to get surprised that my version didn't have GAL
> enabled. But I didn't 

Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Denny Page]

[I hate finding unsent email in my folder :-]

Others may disagree, but I doubt that the type of small temperature variation 
you are referring to has any meaningful effect on tracking. While the datasheet 
for the M8T says that there can be "significant impact" to the specifications 
at “extreme operating temperatures,” it gives the operating temperature as -40 
to +85 C. Simply said, if you can stand to be in the same room/space with it, I 
think you are fine.

Of much greater interest would be the antenna and it’s placement. I’m afraid I 
can’t specifically recommend a “good” antenna, but perhaps others on the list 
can. For my EVK-M8T, I’m using the antenna that came with the kit and it works 
very well. I haven’t tested other antennas with the M8T at this time, but I do 
have a number of other devices with antennas that work well. I also have a few 
antennas that work poorly with all the devices, including the ones with which 
they came. Unfortunately pretty much all of them lack sufficient identification 
markings to identify manufacture/model info.

Regarding placement, I’ve found that in a restricted area even a few inches can 
have a significant impact on the average number of satellites and signal level. 
In my case, it’s associated with the single building structure, but it sounds 
your case is even more restrictive. Although it can be a very lengthy process, 
performing antenna surveys may help improve your situation. For each location, 
you need to monitor the number of satellites and signal level for 24 hours or 
more before determining the relative merit of that location. Repeat… and 
repeat.. and repeat. Determining the very best location for the antenna will 
likely require as many antenna surveys as you have patience for. :)

Hope this helps.

Denny


> On Nov 02, 2017, at 18:54, MLewis  wrote:
> 
> Earlier this week, I put the breakout board with my NEO-M8T into an aluminum 
> can. The can is split into a lower half and an upper half. The lower half was 
> insulated on its sides internally, but open to the upper half, which wasn't 
> insulated. The lower area contains the NEO-M8T on its breakout board and its 
> matching com breakout board.
> 
> In the unusual skyview/RF environment described below:
> - LH was typically showing two or three green sats, with a min of none and a 
> max of five for very brief periods.
> - The average dBc of the green sats was 22 dBc, with a max of 29 dBc.
> - Two screen shots of LH from this time period show an Accu of 12 ns and 33 
> ns.
> 
> This morning, I insulated the inside of the upper half of the can, and added 
> insulation to seal the top of the lower area into a chamber that contained 
> the GPS module board & its com board. Since then, its run for around ten 
> hours, same weather as yesterday except more rain, ambient room temperature 
> wasn't measured but is definitely warmer. Since after around an hour of 
> running:
> - LH has been showing between two and eight green sats, typically three to 
> five:
> - Their average dBc is 30 dBc, with a max of 37 dBc.
> - LH Accu is showing as 6 ns.
> 
> I have no idea what the temperature is inside the chamber.
> 
> As I write this, LH is showing three green sats, at 33, 34 and 35 dBc.
> 
> I expected a more stable internal TCXO in the GPS module, but I didn't expect 
> stronger signals. Although perhaps I should have, as the block diagram for 
> the NEO-M8T does show its TCXO pointing at a "Fractional N Synthesizer" 
> inside the UBX-M8030's "RF Block". It also shows a RTC Crystal for a RTC 
> inside the "Digital Block".
> 
> Is this coincidence or can reception improve with:
> - a higher temperature module?
> - a more stable module temperature?
> 
> I'm tempted to add some thermal mass (block of Al) to the top of the M8T and 
> a chunk of insulation on top of that.
> 
> Michael
> 
> p.s.
> As I finish this, LH is showing five sats, 23, 30, 31, 32 & 34 dBc, Accu 6 ns
> 
> On 01/11/2017 9:55 AM, MLewis wrote:
>> I had anticipated reception issues, which is why I went with the M8T for its 
>> sensitivity, multi-constellation and it's a timing module so a good PPS on a 
>> single sat - only to get surprised that my version didn't have GAL enabled. 
>> But I didn't envision reception would be so bad that not having GAL would be 
>> material.
>> 
>> I'm also too close to that tall building that is reflecting the sats over 
>> the Bering Strait at me. It's a military computer site, which I thought 
>> would be pretty tight on stray RF, but it has antennas. I asked a friend who 
>> works there about my GPS issues and if RF from the site may be influencing 
>> things. He hesitated, then said "'Yes'. That's all I can say."
>> For first power up I had obtained an active antenna for multi-constellation 
>> and a pre-filter that "provides protection from near frequency or strong 
>> harmonic interfering signals."
>> ...
>> 
>> On 01/11/2017 8:45 AM, Bob kb8tq wrote:
>>> Hi
>>> 
>>> For NTP 

Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Bob kb8tq]

Hi

There always is a …. but ….

When you slow down the temperature change process, you increase the 
length of hanging bridges on the pps output. That might not be a big deal
with NTP or in an application that uses the sawtooth correction message.
In an application where a post filter process is expected to average out the
sawtooth, it can be an issue. 

Bob


> On Nov 4, 2017, at 6:16 AM, Leo Bodnar  wrote:
> 
>> From: MLewis
>> Is this coincidence or can reception improve with:
>> - a higher temperature module?
>> - a more stable module temperature?
> 
> Short answer: 
> #2
> 
> Long answer:
> Ublox firmware tracks gradual shifts in its reference frequency (XO, TCXO or 
> external input) and adjusts LO base offset to compensate.
> 
> However, the time constant of this correction tracking loop is quite high 
> (and can be adjusted depending on the reference oscillator type.)
> 
> Sudden changes in temperature and, as a result, in reference frequency result 
> in correlation level drop (seen as sat signal level level drop) or in total 
> loss of tracking and return to acquisition.
> 
> In other words, absolute reference frequency offset (i.e. its temperature) is 
> not a problem - it is gradually compensated for, but sudden shifts in 
> frequency are.
> 
> If your design does (hopefully) does not rely on convection for getting rid 
> of heat, try filling internal voids with cotton wool.  This will stop 
> turbulent (naturally random) and laminar (usually caused by external events) 
> airflows from affecting the reference.  Compartmentalising the design is just 
> another way of separating the airflows but it does not stop them within the 
> compartments.
> 
> There are subtler cases where reference frequency source has a sweet spot 
> where its stability is greatest (like OCXO) and absolute temperature matters 
> as well but this is the first order effect.
> 
> Leo
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Leo Bodnar]

> From: MLewis
> Is this coincidence or can reception improve with:
> - a higher temperature module?
> - a more stable module temperature?

Short answer: 
#2

Long answer:
Ublox firmware tracks gradual shifts in its reference frequency (XO, TCXO or 
external input) and adjusts LO base offset to compensate.

However, the time constant of this correction tracking loop is quite high (and 
can be adjusted depending on the reference oscillator type.)

Sudden changes in temperature and, as a result, in reference frequency result 
in correlation level drop (seen as sat signal level level drop) or in total 
loss of tracking and return to acquisition.

In other words, absolute reference frequency offset (i.e. its temperature) is 
not a problem - it is gradually compensated for, but sudden shifts in frequency 
are.

If your design does (hopefully) does not rely on convection for getting rid of 
heat, try filling internal voids with cotton wool.  This will stop turbulent 
(naturally random) and laminar (usually caused by external events) airflows 
from affecting the reference.  Compartmentalising the design is just another 
way of separating the airflows but it does not stop them within the 
compartments.

There are subtler cases where reference frequency source has a sweet spot where 
its stability is greatest (like OCXO) and absolute temperature matters as well 
but this is the first order effect.

Leo
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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[Gary E. Miller]

Yo MLewis!

On Thu, 2 Nov 2017 21:54:57 -0400
MLewis  wrote:

> I have no idea what the temperature is inside the chamber.

I use the 'temper' to know what temp is in my GPS chamber:

https://www.amazon.com/TEMPer-USB-Thermometer-w-Alerts/dp/B002VA813U

I use that, and an incadescent light bulb, to stabilize my GPS and XO
temps in my chamber.

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

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin


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Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?

[MLewis]

Earlier this week, I put the breakout board with my NEO-M8T into an 
aluminum can. The can is split into a lower half and an upper half. The 
lower half was insulated on its sides internally, but open to the upper 
half, which wasn't insulated. The lower area contains the NEO-M8T on its 
breakout board and its matching com breakout board.


In the unusual skyview/RF environment described below:
- LH was typically showing two or three green sats, with a min of none 
and a max of five for very brief periods.

- The average dBc of the green sats was 22 dBc, with a max of 29 dBc.
- Two screen shots of LH from this time period show an Accu of 12 ns and 
33 ns.


This morning, I insulated the inside of the upper half of the can, and 
added insulation to seal the top of the lower area into a chamber that 
contained the GPS module board & its com board. Since then, its run for 
around ten hours, same weather as yesterday except more rain, ambient 
room temperature wasn't measured but is definitely warmer. Since after 
around an hour of running:
- LH has been showing between two and eight green sats, typically three 
to five:

- Their average dBc is 30 dBc, with a max of 37 dBc.
- LH Accu is showing as 6 ns.

I have no idea what the temperature is inside the chamber.

As I write this, LH is showing three green sats, at 33, 34 and 35 dBc.

I expected a more stable internal TCXO in the GPS module, but I didn't 
expect stronger signals. Although perhaps I should have, as the block 
diagram for the NEO-M8T does show its TCXO pointing at a "Fractional N 
Synthesizer" inside the UBX-M8030's "RF Block". It also shows a RTC 
Crystal for a RTC inside the "Digital Block".


Is this coincidence or can reception improve with:
- a higher temperature module?
- a more stable module temperature?

I'm tempted to add some thermal mass (block of Al) to the top of the M8T 
and a chunk of insulation on top of that.


Michael

p.s.
As I finish this, LH is showing five sats, 23, 30, 31, 32 & 34 dBc, Accu 
6 ns


On 01/11/2017 9:55 AM, MLewis wrote:
I had anticipated reception issues, which is why I went with the M8T 
for its sensitivity, multi-constellation and it's a timing module so a 
good PPS on a single sat - only to get surprised that my version 
didn't have GAL enabled. But I didn't envision reception would be so 
bad that not having GAL would be material.


I'm also too close to that tall building that is reflecting the sats 
over the Bering Strait at me. It's a military computer site, which I 
thought would be pretty tight on stray RF, but it has antennas. I 
asked a friend who works there about my GPS issues and if RF from the 
site may be influencing things. He hesitated, then said "'Yes'. That's 
all I can say."
For first power up I had obtained an active antenna for 
multi-constellation and a pre-filter that "provides protection from 
near  frequency or strong harmonic interfering signals."

...

On 01/11/2017 8:45 AM, Bob kb8tq wrote:

Hi

For NTP levels of accuracy Glonas is quite fine. Combining that with 
GPS should

get you a pretty good “time source” even under your extreme conditions.

Bob

On Oct 31, 2017, at 11:14 PM, MLewis  wrote:

I'm stuck with a near ground level antenna site (~16" above grade?), 
with half a sky view (thankfully to the SSE), less some low blocking 
buildings with regular mutlipath, plus multipath bouncing off a 
taller building to the SE that bounces sats from the NW at me from 
low over the Bering Strait. The building I'm in is concrete with 
flat steel under each floor from the construction method. As I write 
this I'm down to two green sats in LH.


A number of times a day, it will drop to one sat, and there's a few 
dropouts a day where it goes to none of sufficient signal. How many 
times and for how long varies by the day. It's worse when it's wet 
out, which it is right now. If I lower the signal strength 
threshold, then I end up with tons of multipath signals.


...

While I wrote this, LH was typically showing two or three green 
sats, once up to five and once down to one. And I just hit a 
dropout... for a minute and a half; the one remaining green sat went 
behind the corner of the building's entrance canopy, then back out.



On 31/10/2017 10:30 PM, Bob kb8tq wrote:

Hi

Under what conditions would you expect to loose GPS? I seem to be 
able to
do just fine sitting in an armchair here in the family room. That’s 
hardly a

fancy setup.

Bob



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