On the effect of a TID on the frequency of a GPSDO
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Gwyn Griffiths
Jul 11, 2025, 4:22:12 AMJul 11
to HamSCI
In his review of my submission to RSGB RadCom "Upper HF openings at night: one effect of travelling ionospheric disturbances" Dr Peter Duffett-Smith GM3XJE (RadCom Technical Editor) wrote:
"The force of your argument relies on the receivers at the various stations being locked together in frequency by the use of GPSDOs. What is the effect of a TID on the frequency accuracy of a GPSDO? Could it be that your Doppler shifts are actually caused by the oscillators moving in response to the TEC of the ionosphere above the stations, which change as the wave passes by?"
I did not have an answer and could not find an answer online. It is a very good question. It deserved a proper answer, and the answer could be relevant to the wider HamSCI community using PSWS Doppler frequency measurement data.
"The force of your argument relies on the receivers at the various stations being locked together in frequency by the use of GPSDOs. What is the effect of a TID on the frequency accuracy of a GPSDO? Could it be that your Doppler shifts are actually caused by the oscillators moving in response to the TEC of the ionosphere above the stations, which change as the wave passes by?"
I did not have an answer and could not find an answer online. It is a very good question. It deserved a proper answer, and the answer could be relevant to the wider HamSCI community using PSWS Doppler frequency measurement data.
Details of how I obtained an answer are in the attached document, the conclusions are:
1. Suitable data to answer the question have come from frequency measurements of WWV and CHU and an appropriate subset of the HamSCI Personal Space Weather Station network.
2. A Travelling Ionospheric Disturbance (TID) has been shown to have a measurable effect on the frequency variability of a GPS-disciplined Oscillator.
3. An estimate of the level of the effect is that a TID with a variation of 740 mHz RMS observed at 14.67 MHz on a one-hop path induced a frequency variation of about 0.090 mHz RMS on reception of 25 MHz ground wave from WWV due to variations of the 27 MHz clock signal from the receiver GPSDO.
This analysis was made possible due to HamSCI PSWS community contributions: data from Dave Swartz W0DAS for WW0WWV/0, Steve Roberts N4RVE, Michael Hauan for AC0G_ND, and the Maritime Radio Historical Society for KPH; software from Phil Karn KA9Q for ka9q-radio and Rob Robinett AI6VN for WsprDaemon Grape. And of course the HamSCI PSWS database and its designers, coders and funders.
Gwyn G3ZIL
John Ackermann
Jul 11, 2025, 7:52:35 AMJul 11
to HamSCI
Hi Gwyn --
I don't have time right now to post details but I did a several week measurement of several GPSDO to look for effects that could be correlated to space weather. The short answer is that we didn't see any. The long loop time constant of the GPSDO does a good job of eliminating transient effects.
More details later if you'd like.
73,
John
Steve Cerwin
Jul 11, 2025, 7:59:54 AMJul 11
to HamSCI
Excellent Gwyn! It was indeed a good question and needed an answer. Excellent approach and excellent answer. 0.09 mHz out of 740 mHz is negligible. Your data is not far numerically from a wavelength-squared dependence.
Great job!
Steve WA5FRF
From: 'Gwyn Griffiths' via HamSCI <ham...@googlegroups.com>
Sent: Friday, July 11, 2025 2:22 AM
To: HamSCI <ham...@googlegroups.com>
Subject: [HamSCI] On the effect of a TID on the frequency of a GPSDO
Sent: Friday, July 11, 2025 2:22 AM
To: HamSCI <ham...@googlegroups.com>
Subject: [HamSCI] On the effect of a TID on the frequency of a GPSDO
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Gwyn Griffiths
Jul 11, 2025, 9:00:51 AMJul 11
to HamSCI
@John - Interesting, thank you - point taken about the long time constant - more details whenever you have the time, or a copy of what you wrote, would be useful to me. Peter GM3XJE would also be interested as he is to start his own experiment with GPSDO and his Rb oscillator to answer his own question via that route. It was the credibly lagged correlation that swung it for me as a causal correlation.
@Steve - thank you. The wavelength-squared ratio had not struck me, while I also note John's comment on the GPSDO loop time constant as an attenuating factor.
73
Gwyn G3ZIL
John Ackermann N8UR
Jul 11, 2025, 10:42:28 AMJul 11
to 'Gwyn Griffiths' via HamSCI
Hi Gwyn --
Ahead of the 2024 eclipse, I was concerned that GPSDOs might be affected
by whatever it was in the ionosphere we were trying to measure. In
September, 2023 I set up an experiment to monitor several GPSDOs against
a stable reference.
I captured 42 days of data from:
(a) Bodnar Mini
(b) u-blox NEO-M8T raw 10 MHz (so no PLL time constant smoothing)
(c) BG7TBL
(d) Trimble Thunderbolt set to 250 second time constant (relatively
short as typically the constant would be 500 seconds or longer; the
shorter constant should be more susceptible to disturbance).
The four units were on a common antenna and each was hooked to a NanoVNA
with TinyPFA software.* The reference to the NanoVNA was from my
passive maser (shortly before it died; a story for a different day) and
I captured phase comparisons at 0.1 second tau.
The four receivers gave a range of no smoothing (raw u-blox output) to
several hundred seconds. There weren't any really big solar storms
during the period but there were some geomagnetic events.
We (I shared the plots with PhilE and a few others) looked at strip
chart recordings of the relative phase from each of the receivers and
didn't see any obvious jumps that we could correlate to space weather
events.
At that point to be honest I reached the limit of my analytic
capabilities and moved on to other things. I think with more
sophisticated analysis there could be significant things to be learned,
but I just don't have the skills.
If you (or anyone else) would like to play with this data, I'm happy to
share it. The zip file of the raw data is about 1 GB, and I have some
ancillary data available as well (including RINEX data from a
dual-frequency receiver on the same antenna that could be used to
calculate TEC during the period).
So in summary, we didn't see any obvious correlation between GPSDO
output and geomagnetic activity during the test period, but a skilled
analyst might well be able to dig much more out of the data.
73,
John
* TinyPFA is a free software load for the NanoVNA that turns it into a
surprisingly capable frequency and phase analyzer. Its noise floor is
low enough to be useful for a lot of tasks, and the price can't be beat.
----
On 7/11/25 09:00, 'Gwyn Griffiths' via HamSCI wrote:
> @John - Interesting, thank you - point taken about the long time
> constant - more details whenever you have the time, or a copy of what
> you wrote, would be useful to me. Peter GM3XJE would also be interested
> as he is to start his own experiment with GPSDO and his Rb oscillator to
> answer his own question via that route. It was the credibly lagged
> correlation that swung it for me as a causal correlation.
>
> @Steve - thank you. The wavelength-squared ratio had not struck me,
> while I also note John's comment on the GPSDO loop time constant as an
> attenuating factor.
>
> 73
> Gwyn G3ZIL
>
> On Friday, July 11, 2025 at 12:59:54 PM UTC+1 Steve Cerwin wrote:
>
> Excellent Gwyn! It was indeed a good question and needed an answer.
> Excellent approach and excellent answer. 0.09 mHz out of 740 mHz is
> negligible. Your data is not far numerically from a wavelength-
> squared dependence.
> Great job!
> Steve WA5FRF
> ------------------------------------------------------------------------
> *From:* 'Gwyn Griffiths' via HamSCI <ham...@googlegroups.com>
> *Sent:* Friday, July 11, 2025 2:22 AM
> *To:* HamSCI <ham...@googlegroups.com>
> *Subject:* [HamSCI] On the effect of a TID on the frequency of a GPSDO
> In his review of my submission to RSGB RadCom "/Upper HF openings at
> night: one effect of travelling ionospheric disturbances/" Dr Peter
> http://hamsci.org/hamsci-community-participation-guidelines <http://
> hamsci.org/hamsci-community-participation-guidelines>.
> dad2-4ad2-99c0-6c2ee17a06cen%40googlegroups.com?
> utm_medium=email&utm_source=footer>.
> hamsci-community-participation-guidelines>.
> <https://groups.google.com/d/msgid/
> hamsci/8a05d694-0e96-40e9-9c02-9e59804b241bn%40googlegroups.com?
> utm_medium=email&utm_source=footer>.
Ahead of the 2024 eclipse, I was concerned that GPSDOs might be affected
by whatever it was in the ionosphere we were trying to measure. In
September, 2023 I set up an experiment to monitor several GPSDOs against
a stable reference.
I captured 42 days of data from:
(a) Bodnar Mini
(b) u-blox NEO-M8T raw 10 MHz (so no PLL time constant smoothing)
(c) BG7TBL
(d) Trimble Thunderbolt set to 250 second time constant (relatively
short as typically the constant would be 500 seconds or longer; the
shorter constant should be more susceptible to disturbance).
The four units were on a common antenna and each was hooked to a NanoVNA
with TinyPFA software.* The reference to the NanoVNA was from my
passive maser (shortly before it died; a story for a different day) and
I captured phase comparisons at 0.1 second tau.
The four receivers gave a range of no smoothing (raw u-blox output) to
several hundred seconds. There weren't any really big solar storms
during the period but there were some geomagnetic events.
We (I shared the plots with PhilE and a few others) looked at strip
chart recordings of the relative phase from each of the receivers and
didn't see any obvious jumps that we could correlate to space weather
events.
At that point to be honest I reached the limit of my analytic
capabilities and moved on to other things. I think with more
sophisticated analysis there could be significant things to be learned,
but I just don't have the skills.
If you (or anyone else) would like to play with this data, I'm happy to
share it. The zip file of the raw data is about 1 GB, and I have some
ancillary data available as well (including RINEX data from a
dual-frequency receiver on the same antenna that could be used to
calculate TEC during the period).
So in summary, we didn't see any obvious correlation between GPSDO
output and geomagnetic activity during the test period, but a skilled
analyst might well be able to dig much more out of the data.
73,
John
* TinyPFA is a free software load for the NanoVNA that turns it into a
surprisingly capable frequency and phase analyzer. Its noise floor is
low enough to be useful for a lot of tasks, and the price can't be beat.
----
On 7/11/25 09:00, 'Gwyn Griffiths' via HamSCI wrote:
> @John - Interesting, thank you - point taken about the long time
> constant - more details whenever you have the time, or a copy of what
> you wrote, would be useful to me. Peter GM3XJE would also be interested
> as he is to start his own experiment with GPSDO and his Rb oscillator to
> answer his own question via that route. It was the credibly lagged
> correlation that swung it for me as a causal correlation.
>
> @Steve - thank you. The wavelength-squared ratio had not struck me,
> while I also note John's comment on the GPSDO loop time constant as an
> attenuating factor.
>
> 73
> Gwyn G3ZIL
>
> On Friday, July 11, 2025 at 12:59:54 PM UTC+1 Steve Cerwin wrote:
>
> Excellent Gwyn! It was indeed a good question and needed an answer.
> Excellent approach and excellent answer. 0.09 mHz out of 740 mHz is
> negligible. Your data is not far numerically from a wavelength-
> squared dependence.
> Great job!
> Steve WA5FRF
> *From:* 'Gwyn Griffiths' via HamSCI <ham...@googlegroups.com>
> *Sent:* Friday, July 11, 2025 2:22 AM
> *To:* HamSCI <ham...@googlegroups.com>
> *Subject:* [HamSCI] On the effect of a TID on the frequency of a GPSDO
> In his review of my submission to RSGB RadCom "/Upper HF openings at
> night: one effect of travelling ionospheric disturbances/" Dr Peter
> hamsci.org/hamsci-community-participation-guidelines>.
> ---
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Gwyn Griffiths
Jul 11, 2025, 12:00:57 PMJul 11
to HamSCI
Hello John
Thank you for those details. That's a mightily impressive data set that you gathered. It'd be an honour to work on it.
While always considering myself an amateur, I'd be very interested in trying to see what might lie buried in the data using the analysis tools I'm accustomed to. Just a very quick look at the PSWS database shows, for instance, a very nice record with several cycles of a one-hour period TID on 26 September 2023 in the data from Bill Engleke AB4EK Grape1DRF receiver [it truly is wonderful that we can do this]. My approach would be to find such a day in your data and a quiet, control, day and see what may be there.
73
Gwyn
Bob Gerzoff
Jul 11, 2025, 2:17:56 PMJul 11
to ham...@googlegroups.com
I hear data, I'm interested.
A couple of quick questions:
- What specific questions might one be looking to explore or model using these data?
- Is there are data dictionary available?
- Unzipped how many gigs are we talking about?
I’ve attached a bibliography. It would appear there has been previous work in the area.
73,
Bob WK2Y
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Phil Erickson
Jul 11, 2025, 2:21:25 PMJul 11
to ham...@googlegroups.com
Hi Bob,
Your first question is the right one. There is an entire huge body of literature and a long standing working community on ionospheric effects for GNSS navigation - but the topics are vast, so narrowing down the exact purpose similar to what John and Gwyn are circling around in the previous emails.
73
Phil W1PJE
To view this discussion visit https://groups.google.com/d/msgid/hamsci/MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com.
Gwyn Griffiths
Jul 11, 2025, 2:52:44 PMJul 11
to HamSCI
Hello Bob,
The two very specific questions were in the second paragraph of my first post and in the document I attached.
Yes, there is a vast literature and careers are spent in the topic, but when you want a specific answer, as I did, to be directly applicable to the measurements we are making, the simple experiment seemed, to me, to be the quickest approach.
regards
Gwyn
Bob Gerzoff
Jul 11, 2025, 3:02:48 PMJul 11
to ham...@googlegroups.com
I missed the email with the attachment. Let me go back and look.
To view this discussion visit https://groups.google.com/d/msgid/hamsci/22c2c7ed-0012-4c2a-ae81-b580734c6e89n%40googlegroups.com.
John Ackermann N8UR
Jul 12, 2025, 7:14:26 AMJul 12
to ham...@googlegroups.com
I'd be honored to have you work on my data, Gwyn! :-)
I've put the whole data set at
https://febo.com/pages/2023_gpsdo_geotest/
The main files are:
2023_geotest_rinex.zip 2023-11-22 19:05 185M
-- RINEX files from Mosaic-T dual freq GNSS
2023_geotest_timelab.zip 2023-11-22 19:09 618M
-- Raw files after opening and saving in TimeLab
2023_gps_geotest_original_files.zip 2023-10-27 19:43 899M
-- Original phase files
bodnar_vs_maser_48h_4Dec2023.tim 2023-12-07 19:03 692M
-- a separate TimeLab dataset (not sure why I saved this)
cme_01Dec2023_timelab.zip 2023-12-03 15:48 333M
-- Timelab file recorded during a CME
The README and METADATA files give more information.
Note that the ".tim" files are in the format created by John Miles'
KE5FX TimeLab software which has become the de facto standard for time
and frequency analysis. IT's FOSS and can be downloaded from
https://www.miles.io/timelab/beta.htm. I highly recommend it; John has
done a wonderful job pulling all the T&F analysis tools together. If
you want to get back to original phase or frequency data, the program
can export raw text files.
I'm happy to help with any questions about the data.
73,
John
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I've put the whole data set at
https://febo.com/pages/2023_gpsdo_geotest/
The main files are:
2023_geotest_rinex.zip 2023-11-22 19:05 185M
-- RINEX files from Mosaic-T dual freq GNSS
2023_geotest_timelab.zip 2023-11-22 19:09 618M
-- Raw files after opening and saving in TimeLab
2023_gps_geotest_original_files.zip 2023-10-27 19:43 899M
-- Original phase files
bodnar_vs_maser_48h_4Dec2023.tim 2023-12-07 19:03 692M
-- a separate TimeLab dataset (not sure why I saved this)
cme_01Dec2023_timelab.zip 2023-12-03 15:48 333M
-- Timelab file recorded during a CME
The README and METADATA files give more information.
Note that the ".tim" files are in the format created by John Miles'
KE5FX TimeLab software which has become the de facto standard for time
and frequency analysis. IT's FOSS and can be downloaded from
https://www.miles.io/timelab/beta.htm. I highly recommend it; John has
done a wonderful job pulling all the T&F analysis tools together. If
you want to get back to original phase or frequency data, the program
can export raw text files.
I'm happy to help with any questions about the data.
73,
John
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John Ackermann N8UR
Jul 12, 2025, 7:14:34 AMJul 12
to ham...@googlegroups.com
Bob, in the data directory I linked to there are a couple of files with
info about the data. In short, the raw data for the main test is a set
of text files with phase of the GPSDO under test relative to the
reference standard. Each line is a phase value at 0.1 second intervals.
As I mentioned in my other message, there are also files in the
"TimeLab" file format. I recommend looking at those with the free
TimeLab software, which can export the data as ASCII phase files if desired.
Finally, there is a set of RINEX files from a dual-frequency GNSS
receiver which contain raw satellite data -- carrier phase, doppler,
signal strength, etc. That data can be processed to extract TEC values,
among other things.
73,
John
----
On 7/11/25 14:17, Bob Gerzoff wrote:
> I hear data, I'm interested.
>
> A couple of quick questions:
>
> * What specific questions might one be looking to explore or model
> using these data?
>
> * Is there are data dictionary available?
>
> * Unzipped how many gigs are we talking about?
> *To:* HamSCI <ham...@googlegroups.com>
> *Subject:* Re: [HamSCI] On the effect of a TID on the frequency of a GPSDO
> <http://hamsci.org/hamsci-community-participation-guidelines> <http://
info about the data. In short, the raw data for the main test is a set
of text files with phase of the GPSDO under test relative to the
reference standard. Each line is a phase value at 0.1 second intervals.
As I mentioned in my other message, there are also files in the
"TimeLab" file format. I recommend looking at those with the free
TimeLab software, which can export the data as ASCII phase files if desired.
Finally, there is a set of RINEX files from a dual-frequency GNSS
receiver which contain raw satellite data -- carrier phase, doppler,
signal strength, etc. That data can be processed to extract TEC values,
among other things.
73,
John
----
On 7/11/25 14:17, Bob Gerzoff wrote:
> I hear data, I'm interested.
>
> A couple of quick questions:
>
> using these data?
>
> * Is there are data dictionary available?
>
> * Unzipped how many gigs are we talking about?
>
> I’ve attached a bibliography. It would appear there has been previous
> work in the area.
>
> 73,
>
> Bob WK2Y
>
> I’ve attached a bibliography. It would appear there has been previous
> work in the area.
>
> 73,
>
> Bob WK2Y
>
> *From:*'Gwyn Griffiths' via HamSCI <ham...@googlegroups.com>
> *Sent:* Friday, July 11, 2025 12:01 PM
> *To:* HamSCI <ham...@googlegroups.com>
> *Subject:* Re: [HamSCI] On the effect of a TID on the frequency of a GPSDO
> > hamsci.org/hamsci-community-participation-guidelines <http://
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Lawrence Naif
Jul 12, 2025, 7:14:47 AMJul 12
to ham...@googlegroups.com
I hear data and questions regarding ionospheric effects for GNSS navigation-I am interested.
I am working on a model to identify TIDs .. This is a short movie of the change in the Quanternion norm, a composite metric derived from ionospheric parameters derived from the COSMIC-2 Data, Near Real-Time Operational Datasets: COSMIC-2 data processed operationally in near-real time for the Absolute total electron content. The period is 7-8 April 2024 across all 192 GPS-LEO combinations. The object is to use this data as a potential one of a range of warning metrics for detection of periods of Ionospheric risk that can potentially lead to disruptions in satellite-based systems., A higher norm value indicates greater combined variability in underlying ionospheric risk drivers, suggesting increased ionospheric activity.
Check the attached video
Regards,
Lawrence
To view this discussion visit https://groups.google.com/d/msgid/hamsci/22c2c7ed-0012-4c2a-ae81-b580734c6e89n%40googlegroups.com.
Bob Gerzoff
Jul 12, 2025, 8:01:21 AMJul 12
to ham...@googlegroups.com
Good morning Gwyn,
Now that I’ve actually looked at the emails and paper and at the risk of oversimplifying, tell me if I’m getting the point:
You suggest we compare “TID active” vs TID control periods and compare the relative phase variability or possibly phase excursions in those two periods. Makes sense. Sounds to me like an interrupted time series analysis, but that would depend on how details of the phase variability series and the definition of TID active and control periods. Certainly want to look at it graphically, regardless.
Am I on the right track or am I missing the mark?
Bob
To view this discussion visit https://groups.google.com/d/msgid/hamsci/22c2c7ed-0012-4c2a-ae81-b580734c6e89n%40googlegroups.com.
Gwyn Griffiths
Jul 12, 2025, 10:06:36 AMJul 12
to HamSCI
John,
Thank you for the link to the data directory. At least to begin with I have I have downloaded the 2023_gps_geotest_original_files.zip file and the metadata and readme files. All seems pretty clear to me at this stage. I do have a nanVNA H4 with PFA software here from tests I did a while ago with Glenn N6GN's early GERT boards and a Bodnar etc. so have trodden part of this analysis path before. I'll start with the mini-Bodnar. Its frequency offset is helpful in that I should see it - if I don't, I'm doing something wrong.
Bob,
You are certainly on the right track. I tend to explore and learn as I go along, and I am a 'small data' person at heart. In the context of John's data I would start with the TID active and TID quiet periods both on the same day. The record from Bill Engleke's Grape1DRF at
for 26 September 2023 is a really nice example, and the GPSDO data lies at the end of John's "0556" files (see metadata.txt). On that day I'd classify 0000-0200 UTC and 0400-0600 UTC as TID-quiet and 0600-0800 and 0900-1100 UTC as TID active.
I'm right with you on having a graphical look as well as numerics.
73
Gwyn G3ZIL
Terry Bullett
Jul 12, 2025, 9:56:02 PMJul 12
to ham...@googlegroups.com
All,
From a propagation perspective, the ionosphere causes a delay in the time and phase path of the radio signal from each satellite to your receiver. For a single frequency receiver, "most" of the ionosphere is taken out by a simple, single parameter ionosphere model, developed at AFRL back in the early days of GPS (1990's). This model is built into most receivers but can not account for space weather, never mind a TID. That is why there are 2 GPS frequencies.
If a TID changes the slant total electron content (TEC) of the ionosphere with time, this will cause a shift in the timing of the GPS 1PPS that most DO's use to tweak their clock. Just as such an event will cause the navigation solution to vary.
The TID changes the slant TEC in 2 primary ways:
Changing the length of the slant path in the ionosphere
Changing the ionosphere density by pushing it out of photo-chemical equilibrium, upsetting the balance of ionization production and loss that is achieved if there is no plasma transport.
Mathematically, the GPS receiver is solving an ill-defined geometry equation with 4 variables (Lat, Lon, Alt and Time) from nominally 4 to 12 data points. And all data have errors. So it becomes a matter of where the receiver 'puts' the uncertainty. The Trimble Resolution T receivers are meant for Fixed Base Operations, so it 'learns' it physical location and just deals with the time variable.
What the "cheap" GPSDO'd do is probably undocumented.
I suggest looking up "Allan Variance" The statistics of this is very elegant, often employing Baysen techniques that are hard to wrap your head around. NIST in Boulder uses these techniques to provide accuracy, precision and uncertainties on their timing data.
NIST provides the timing for WWV, but the US Navy Observatory provides the GPS reference.
But since the Boulder clock and the DC clock are about 6000 ft difference in the Earth's gravity well, the clocks run at different speeds due to General Relativity.
For this same reason, the moving GPS satellites dropping radio photons into the Earth's gravity well have their atomic clock adjusted for these Einstein effects.
Good luck not going crazy chasing every last femtosecond out of your data!
Like Jimmy Buffet said: "What time is it anyway? It's 5'oclock somewhere."
73.
Terry W0ASP
From a propagation perspective, the ionosphere causes a delay in the time and phase path of the radio signal from each satellite to your receiver. For a single frequency receiver, "most" of the ionosphere is taken out by a simple, single parameter ionosphere model, developed at AFRL back in the early days of GPS (1990's). This model is built into most receivers but can not account for space weather, never mind a TID. That is why there are 2 GPS frequencies.
If a TID changes the slant total electron content (TEC) of the ionosphere with time, this will cause a shift in the timing of the GPS 1PPS that most DO's use to tweak their clock. Just as such an event will cause the navigation solution to vary.
The TID changes the slant TEC in 2 primary ways:
Changing the length of the slant path in the ionosphere
Changing the ionosphere density by pushing it out of photo-chemical equilibrium, upsetting the balance of ionization production and loss that is achieved if there is no plasma transport.
Mathematically, the GPS receiver is solving an ill-defined geometry equation with 4 variables (Lat, Lon, Alt and Time) from nominally 4 to 12 data points. And all data have errors. So it becomes a matter of where the receiver 'puts' the uncertainty. The Trimble Resolution T receivers are meant for Fixed Base Operations, so it 'learns' it physical location and just deals with the time variable.
What the "cheap" GPSDO'd do is probably undocumented.
I suggest looking up "Allan Variance" The statistics of this is very elegant, often employing Baysen techniques that are hard to wrap your head around. NIST in Boulder uses these techniques to provide accuracy, precision and uncertainties on their timing data.
NIST provides the timing for WWV, but the US Navy Observatory provides the GPS reference.
But since the Boulder clock and the DC clock are about 6000 ft difference in the Earth's gravity well, the clocks run at different speeds due to General Relativity.
For this same reason, the moving GPS satellites dropping radio photons into the Earth's gravity well have their atomic clock adjusted for these Einstein effects.
Good luck not going crazy chasing every last femtosecond out of your data!
Like Jimmy Buffet said: "What time is it anyway? It's 5'oclock somewhere."
73.
Terry W0ASP
To view this discussion visit https://groups.google.com/d/msgid/hamsci/8e9c982e-6bfd-4ffd-8740-ad0e2f0cf8dcn%40googlegroups.com.
-- Dr. Terry Bullett WØASP NOAA National Centers for Environmental Information (NOAA/NCEI) Cooperative Institute for Research in Environmental Sciences (CIRES) Terry....@noaa.gov 720-446-9775 (google voice) 978-337-9092 (cell) "Life is Complex. It has a Real part and an Imaginary part."
John Ackermann N8UR
Jul 12, 2025, 10:06:20 PMJul 12
to ham...@googlegroups.com
Regarding the solution used, "timing" GPSs allow you for a fixed
location, either by manual entry or by doing a self-survey and averaging
the results over several hours. With a fixed position, they only need
to solve for one variable (time).
Most commercial GPSDOs (like HP/Agilent/Symmetricom Z38xx or Trimble
Thunderbolt) use timing receivers and fixed position. The cheaper
GPSDOs -- who knows?
In the test data Gwyn and others are playing with, the u-blox M8T and
Trimble Thunderbolt were both set to fixed location "0D" mode, while the
BG7TBL and Bodnar units don't have provision for that.
If the satellite geometry is good, there isn't a lot of timing
performance difference between "3D" and "0D" solutions. But if the
geometry is bad, the the 0D timing performance tends to hold together
much better.
73,
John
----
>> *To:* HamSCI <ham...@googlegroups.com>
>> *Subject:* Re: [HamSCI] On the effect of a TID on the frequency of
>>
>> * Unzipped how many gigs are we talking about?
>> *To:* HamSCI <ham...@googlegroups.com>
>> *Subject:* Re: [HamSCI] On the effect of a TID on the
>> > <https://groups.google.com/d/msgid/hamsci/46973e7a-
>> > dad2-4ad2-99c0-6c2ee17a06cen%40googlegroups.com
>> <http://40googlegroups.com>?
>> groups.google.com/d/msgid/
>> >
>> hamsci/8a05d694-0e96-40e9-9c02-9e59804b241bn%40googlegroups.com <http://40googlegroups.com>
>> > <https://groups.google.com/d/msgid/
>> >
>> hamsci/8a05d694-0e96-40e9-9c02-9e59804b241bn%40googlegroups.com <http://40googlegroups.com>?
>> a022-97a6453b6c19n%40googlegroups.com <https://
>> groups.google.com/d/msgid/hamsci/d03b21d9-2bf8-43cb-
>> a022-97a6453b6c19n%40googlegroups.com?
>> b580734c6e89n%40googlegroups.com?utm_medium=email&utm_source=footer>.
>> <https://groups.google.com/d/msgid/hamsci/8e9c982e-6bfd-4ffd-8740-
>> ad0e2f0cf8dcn%40googlegroups.com?utm_medium=email&utm_source=footer>.
> groups.google.com/d/msgid/hamsci/7caab4a8-
> b76d-436f-9032-8813139090d7%40noaa.gov?utm_medium=email&utm_source=footer>.
location, either by manual entry or by doing a self-survey and averaging
the results over several hours. With a fixed position, they only need
to solve for one variable (time).
Most commercial GPSDOs (like HP/Agilent/Symmetricom Z38xx or Trimble
Thunderbolt) use timing receivers and fixed position. The cheaper
GPSDOs -- who knows?
In the test data Gwyn and others are playing with, the u-blox M8T and
Trimble Thunderbolt were both set to fixed location "0D" mode, while the
BG7TBL and Bodnar units don't have provision for that.
If the satellite geometry is good, there isn't a lot of timing
performance difference between "3D" and "0D" solutions. But if the
geometry is bad, the the 0D timing performance tends to hold together
much better.
73,
John
----
>> *From:*'Gwyn Griffiths' via HamSCI <ham...@googlegroups.com>
>> *Sent:* Friday, July 11, 2025 2:53 PM
>> *To:* HamSCI <ham...@googlegroups.com>
>> *Subject:* Re: [HamSCI] On the effect of a TID on the frequency of
>> a GPSDO
>>
>> Hello Bob,
>>
>> The two very specific questions were in the second paragraph of my
>> first post and in the document I attached.
>>
>> Yes, there is a vast literature and careers are spent in the
>> topic, but when you want a specific answer, as I did, to be
>> directly applicable to the measurements we are making, the simple
>> experiment seemed, to me, to be the quickest approach.
>>
>> regards
>>
>> Gwyn
>>
>> On Friday, July 11, 2025 at 7:21:25 PM UTC+1 phil.erickson wrote:
>>
>> Hi Bob,
>>
>> Your first question is the right one. There is an entire
>> huge body of literature and a long standing working community
>> on ionospheric effects for GNSS navigation - but the topics
>> are vast, so narrowing down the exact purpose similar to what
>> John and Gwyn are circling around in the previous emails.
>>
>> 73
>>
>> Phil W1PJE
>>
>> On Fri, Jul 11, 2025 at 2:17 PM Bob Gerzoff
>> <b...@bobgerzoff.com> wrote:
>>
>> I hear data, I'm interested.
>>
>> A couple of quick questions:
>>
>> * What specific questions might one be looking to
>>
>> Hello Bob,
>>
>> The two very specific questions were in the second paragraph of my
>> first post and in the document I attached.
>>
>> Yes, there is a vast literature and careers are spent in the
>> topic, but when you want a specific answer, as I did, to be
>> directly applicable to the measurements we are making, the simple
>> experiment seemed, to me, to be the quickest approach.
>>
>> regards
>>
>> Gwyn
>>
>> On Friday, July 11, 2025 at 7:21:25 PM UTC+1 phil.erickson wrote:
>>
>> Hi Bob,
>>
>> Your first question is the right one. There is an entire
>> huge body of literature and a long standing working community
>> on ionospheric effects for GNSS navigation - but the topics
>> are vast, so narrowing down the exact purpose similar to what
>> John and Gwyn are circling around in the previous emails.
>>
>> 73
>>
>> Phil W1PJE
>>
>> On Fri, Jul 11, 2025 at 2:17 PM Bob Gerzoff
>> <b...@bobgerzoff.com> wrote:
>>
>> I hear data, I'm interested.
>>
>> A couple of quick questions:
>>
>> explore or model using these data?
>>
>> * Is there are data dictionary available?
>>
>>
>> * Unzipped how many gigs are we talking about?
>>
>> I’ve attached a bibliography. It would appear there has
>> been previous work in the area.
>>
>> 73,
>>
>> Bob WK2Y
>>
>> I’ve attached a bibliography. It would appear there has
>> been previous work in the area.
>>
>> 73,
>>
>> Bob WK2Y
>>
>> *From:*'Gwyn Griffiths' via HamSCI <ham...@googlegroups.com>
>> *Sent:* Friday, July 11, 2025 12:01 PM
>> *To:* HamSCI <ham...@googlegroups.com>
>> *Subject:* Re: [HamSCI] On the effect of a TID on the
>> > hamsci.org/hamsci-community-participation-guidelines
>> <http://hamsci.org/hamsci-community-participation-
>> guidelines>>.
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>
> --
> Dr. Terry Bullett WØASP
> NOAA National Centers for Environmental Information (NOAA/NCEI)
> Cooperative Institute for Research in Environmental Sciences (CIRES)
> Terry....@noaa.gov 720-446-9775 (google voice) 978-337-9092 (cell)
> "Life is Complex. It has a Real part and an Imaginary part."
>
> --
> Dr. Terry Bullett WØASP
> NOAA National Centers for Environmental Information (NOAA/NCEI)
> Cooperative Institute for Research in Environmental Sciences (CIRES)
> Terry....@noaa.gov 720-446-9775 (google voice) 978-337-9092 (cell)
> "Life is Complex. It has a Real part and an Imaginary part."
>
> --
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Lawrence Naif
Jul 13, 2025, 12:15:36 AMJul 13
to ham...@googlegroups.com
HI All,
I am exploring and learning as I go along. For the single-parameter ionosphere model, developed at AFRL back in the early days of GPS (1990s), is this the "Klobuchar Ionospheric Model"?
Additionally, for reference, I am using the Ionospheric Radio Propagation model by the Department of Commerce. Anything newer and comprehensive, including models?
Regards,
To view this discussion visit https://groups.google.com/d/msgid/hamsci/7caab4a8-b76d-436f-9032-8813139090d7%40noaa.gov.
Terry Bullett
Jul 13, 2025, 12:15:41 AMJul 13
to ham...@googlegroups.com
John
I use an SRS rubidium GPSDO for long term stability, then a Wenzell PLL quartz oscillator for low phase noise. This is a very expensive package, well outside the budget of most Hams. But phase noise is is the second worst enemy to a digital receiver. My combination has very good Allan variance, which SRS has documented, but I have the luxury of receiving WWV via ground wave so I have the 'better' reference it takes to measure the Allan variance. And I have a specification for 'good enough' and do not need to spend effort doing better, And I appreciate the effort of those who want to do better. Godspeed to all you out there.
Remember, that first and foremost, everything is a thermometer. Temperature stability is a Must Have. Otherwise you are chasing the weather.
All of these time errors are like manure. There is a fixed amount over a day, and you can eat it all at once or spread it out over time and take small bites, Depends on how you like your manure....
As you note, how this is spread out depends on the design of the PLL's in the GPSDO.
Best of luck with this,
73
Terry, W0ASP
I use an SRS rubidium GPSDO for long term stability, then a Wenzell PLL quartz oscillator for low phase noise. This is a very expensive package, well outside the budget of most Hams. But phase noise is is the second worst enemy to a digital receiver. My combination has very good Allan variance, which SRS has documented, but I have the luxury of receiving WWV via ground wave so I have the 'better' reference it takes to measure the Allan variance. And I have a specification for 'good enough' and do not need to spend effort doing better, And I appreciate the effort of those who want to do better. Godspeed to all you out there.
Remember, that first and foremost, everything is a thermometer. Temperature stability is a Must Have. Otherwise you are chasing the weather.
All of these time errors are like manure. There is a fixed amount over a day, and you can eat it all at once or spread it out over time and take small bites, Depends on how you like your manure....
As you note, how this is spread out depends on the design of the PLL's in the GPSDO.
Best of luck with this,
73
Terry, W0ASP
Gwyn Griffiths
Jul 24, 2025, 6:57:29 AMJul 24
to HamSCI
My thanks to John Ackerman N8UR for making available his dataset of the phase differences of four GPSDOs against a passive maser.
I identified the 26th September 2023 as a day within his dataset with a TID well-measured by the PSWS network.
My conclusions are set out below. The detail is in the attached pdf.
Conclusions
1. For the uBlox M8T and BG7TBL GPSDOs the inherent time-varying phase offsets (equal to ~130 μHz and ~390 μHz RMS at 10 MHz) were too large for a TID-induced effect to be seen.
2. For the Thunderbolt there was modest evidence that a TID with ~0.35 Hz Doppler at 10 MHz did have an effect, contributing ~8% to the GPSDO's frequency offset variance, equivalent to ~15 μHz of the RMS of ~52 μHz. There was strong evidence that a TID with ~0.65 Hz Doppler at 10 MHz contributed ~28% at its peak to the GPSDO's frequency offset variance, equivalent to ~21 μHz of the RMS of ~39 μHz.
3. For the Mini-Bodnar there was strong evidence that a TID with ~0.35 Hz Doppler at 10 MHz did have an effect, contributing ~26% to the GPSDO's frequency offset variance, equivalent to ~20 μHz of the RMS of ~40 μHz. A TID with ~0.65 Hz Doppler at 10 MHz contributed ~31% at its peak to the GPSDO's frequency offset variance, equivalent to ~47 μHz of the RMS of ~81 μHz.
4. Where a TID-induced effect was seen on the Thunderbolt and Mini-Bodnar GPSDOs it was first clearly observed and quantified using a cross-correlation, matched filter analysis as it was 'within the noise'.
5. With the TID effect confirmed on the Mini-Bodnar via cross-correlation the peak at 3300 seconds (55 minutes) in the Allan Deviation could confidently be ascribed to the TID.
GwynG3ZIL
HL Serra
Jul 24, 2025, 12:47:44 PMJul 24
to ham...@googlegroups.com
Thanks, Gwyn. So if I'm reading your data analysis correctly, the Thunderbolt is the "best" of those analyzed? Or to your experience is there an even better GPSDO unit under $300? (I ask b/c I'm thinking of getting another GPSDO.)
73 Larry
To view this discussion visit https://groups.google.com/d/msgid/hamsci/9f0647c0-5f76-4e0e-a07e-8b0a6270aaebn%40googlegroups.com.
John Ackermann N8UR
Jul 24, 2025, 2:35:05 PMJul 24
to ham...@googlegroups.com
Hi Larry --
The Thunderbolt was pretty clearly the best of the four units in the test.
Choosing a GPSDO can be challenging because there are a lot of units
available with questionable backgrounds (e.g., most of the ones on eBay
these days). In general, units with oven-controlled oscillators (like
the Thunderbolt) are better than units with temperature-controlled
oscillators (like the Bodnar), though there are exceptions to that rule.
For example, the BG7TBL unit in the test had a pretty decent 10 MHz
OCXO and should have performed much better than it did. It was hampered
by defects in its control loop hardware or firmware.
I did a four-part blog series on Oscillators, GPS, and GPSDOs that tries
to explain how they work and what the critical design considerations
are. Part 1 is at https://blog.febo.com/?p=871 -- though part 4 has the
juicy stuff you're probably most interested in, including a comparison
of some GPSDO.
The BG7TBL GPSDOs have their own set of confusions, as several different
designs have been sold under that generic name, and they have wildly
different performance. I tested four of them in this blog posting:
https://blog.febo.com/?p=636
There are lots of units on eBay that seem to be legitimate Trimble or
HP/Agilent/Symmetricom, but are in fact rebuilt from scrap parts. Some
of those might work very well, but the eBay descriptions are often very
misleading if not downright incorrect. Be very cautious when buying one
of those.
73,
John
----
On 7/24/25 11:09, HL Serra wrote:
> Thanks, Gwyn. So if I'm reading your data analysis correctly, the
> Thunderbolt is the "best" of those analyzed? Or to your experience is
> there an even better GPSDO unit under $300? (I ask b/c I'm thinking of
> getting another GPSDO.)
> 73 Larry
>
> On Thu, Jul 24, 2025 at 3:57 AM 'Gwyn Griffiths' via HamSCI
> <ham...@googlegroups.com <mailto:ham...@googlegroups.com>> wrote:
>
> My thanks to John Ackerman N8UR for making available his dataset of
> the phase differences of four GPSDOs against a passive maser.
> I identified the 26th September 2023 as a day within his dataset
> with a TID well-measured by the PSWS network.
> My conclusions are set out below. The detail is in the attached pdf.
>
> *Conclusions*
>
> 1.For the *uBlox M8T* and *BG7TBL* GPSDOs the inherent time-varying
> *Mini-Bodnar* GPSDOs it was first clearly observed and quantified
>
> __
>>>> select_download_range/29588/ <https://
>>>> pswsnetwork.caps.ua.edu/observations/
>>>> select_download_range/29588/>
>>>> participation <http://hamsci.org/hamsci-community-
>>>> participation>-
>>>> guidelines <http://
>>>> hamsci.org/hamsci-community-participation>-
>>>> > hamsci/46973e7a-
>>>> dad2-4ad2-99c0-6c2ee17a06cen%40googlegroups.com
>>>> <http://40googlegroups.com>
>>>> <http://40googlegroups.com> <http://40googlegroups.com>
>>>> > <https://groups.google.com/d/msgid/
>>>> hamsci/46973e7a <https://groups.google.com/d/msgid/
>>>> participation-guidelines>
>>>> <http://hamsci.org/hamsci-community-participation <http://
>>>> hamsci.org/hamsci-community-participation>-
>>>> >
>>>> hamsci/8a05d694-0e96-40e9-9c02-9e59804b241bn%40googlegroups.com <http://40googlegroups.com> <http://40googlegroups.com> <http://40googlegroups.com>
>>>> > <https://groups.google.com/d/msgid/
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>>>> hamsci/8a05d694-0e96-40e9-9c02-9e59804b241bn%40googlegroups.com <http://40googlegroups.com> <http://40googlegroups.com> <http://40googlegroups.com>?
>>>> msgid/hamsci/d03b21d9-2bf8-43cb-
>>>> a022-97a6453b6c19n%40googlegroups.com
>>>> <http://40googlegroups.com> <https://
>>>> groups.google.com/d/msgid/hamsci/d03b21d9-2bf8-43cb-
>>>> <http://groups.google.com/d/msgid/hamsci/d03b21d9-2bf8-43cb->
>>>> a022-97a6453b6c19n%40googlegroups.com
>>>> msgid/hamsci/
>>>> MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com <http://40MW5PR13MB5464.namprd13.prod.outlook.com> <https://groups.google.com/d/msgid/hamsci/MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com?utm_medium=email&utm_source=footer> <https://groups.google.com/d/msgid/hamsci/MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com?utm_medium=email&utm_source=footer>.
>>>> ---
>>>> hamsci/22c2c7ed-0012-4c2a-ae81-
>>>> b580734c6e89n%40googlegroups.com <http://40googlegroups.com>
>>>> <https://groups.google.com/d/msgid/
>>>> hamsci/22c2c7ed-0012-4c2a-ae81 <https://groups.google.com/d/
>>>> msgid/hamsci/22c2c7ed-0012-4c2a-ae81>-
>>>> b580734c6e89n%40googlegroups.com?
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>>> (google voice) 978-337-9092 <tel:(978)%20337-9092> (cell)
>>> community-participation-guidelines>.
>>> ---
>>> b76d-436f-9032-8813139090d7%40noaa.gov <http://40noaa.gov>
>>> <https:// groups.google.com/d/msgid/hamsci/7caab4a8-
>>> b76d-436f-9032-8813139090d7%40noaa.gov?
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>>> b76d-436f-9032-8813139090d7%40noaa.gov?
> hamsci.org/hamsci-community-participation-guidelines>.
> ---
> <https://groups.google.com/d/msgid/hamsci/9f0647c0-5f76-4e0e-
> a07e-8b0a6270aaebn%40googlegroups.com?
> <https://groups.google.com/d/msgid/hamsci/
> CAM4%3DgM9BZLm47685yMZdujk1AgB7Uycwb2wmhEjvhn%2B9zb13Xg%40mail.gmail.com?utm_medium=email&utm_source=footer>.
The Thunderbolt was pretty clearly the best of the four units in the test.
Choosing a GPSDO can be challenging because there are a lot of units
available with questionable backgrounds (e.g., most of the ones on eBay
these days). In general, units with oven-controlled oscillators (like
the Thunderbolt) are better than units with temperature-controlled
oscillators (like the Bodnar), though there are exceptions to that rule.
For example, the BG7TBL unit in the test had a pretty decent 10 MHz
OCXO and should have performed much better than it did. It was hampered
by defects in its control loop hardware or firmware.
I did a four-part blog series on Oscillators, GPS, and GPSDOs that tries
to explain how they work and what the critical design considerations
are. Part 1 is at https://blog.febo.com/?p=871 -- though part 4 has the
juicy stuff you're probably most interested in, including a comparison
of some GPSDO.
The BG7TBL GPSDOs have their own set of confusions, as several different
designs have been sold under that generic name, and they have wildly
different performance. I tested four of them in this blog posting:
https://blog.febo.com/?p=636
There are lots of units on eBay that seem to be legitimate Trimble or
HP/Agilent/Symmetricom, but are in fact rebuilt from scrap parts. Some
of those might work very well, but the eBay descriptions are often very
misleading if not downright incorrect. Be very cautious when buying one
of those.
73,
John
----
On 7/24/25 11:09, HL Serra wrote:
> Thanks, Gwyn. So if I'm reading your data analysis correctly, the
> Thunderbolt is the "best" of those analyzed? Or to your experience is
> there an even better GPSDO unit under $300? (I ask b/c I'm thinking of
> getting another GPSDO.)
> 73 Larry
>
> On Thu, Jul 24, 2025 at 3:57 AM 'Gwyn Griffiths' via HamSCI
> <ham...@googlegroups.com <mailto:ham...@googlegroups.com>> wrote:
>
> My thanks to John Ackerman N8UR for making available his dataset of
> the phase differences of four GPSDOs against a passive maser.
> I identified the 26th September 2023 as a day within his dataset
> with a TID well-measured by the PSWS network.
> My conclusions are set out below. The detail is in the attached pdf.
>
>
> 1.For the *uBlox M8T* and *BG7TBL* GPSDOs the inherent time-varying
> phase offsets (equal to ~130 μHz and ~390 μHz RMS at 10 MHz) were
> too large for a TID-induced effect to be seen.
>
> 2.For the *Thunderbolt* there was modest evidence that a TID with
> too large for a TID-induced effect to be seen.
>
> ~0.35 Hz Doppler at 10 MHz did have an effect, contributing ~8% to
> the GPSDO's frequency offset variance, equivalent to ~15 μHz of the
> RMS of ~52 μHz. There was strong evidence that a TID with ~0.65 Hz
> Doppler at 10 MHz contributed ~28% at its peak to the GPSDO's
> frequency offset variance, equivalent to ~21 μHz of the RMS of ~39 μHz.
>
> 3.For the *Mini-Bodnar* there was strong evidence that a TID with
> the GPSDO's frequency offset variance, equivalent to ~15 μHz of the
> RMS of ~52 μHz. There was strong evidence that a TID with ~0.65 Hz
> Doppler at 10 MHz contributed ~28% at its peak to the GPSDO's
> frequency offset variance, equivalent to ~21 μHz of the RMS of ~39 μHz.
>
> ~0.35 Hz Doppler at 10 MHz did have an effect, contributing ~26% to
> the GPSDO's frequency offset variance, equivalent to ~20 μHz of the
> RMS of ~40 μHz. A TID with ~0.65 Hz Doppler at 10 MHz contributed
> ~31% at its peak to the GPSDO's frequency offset variance,
> equivalent to ~47 μHz of the RMS of ~81 μHz.
>
> 4.Where a TID-induced effect was seen on the *Thunderbolt* and
> the GPSDO's frequency offset variance, equivalent to ~20 μHz of the
> RMS of ~40 μHz. A TID with ~0.65 Hz Doppler at 10 MHz contributed
> ~31% at its peak to the GPSDO's frequency offset variance,
> equivalent to ~47 μHz of the RMS of ~81 μHz.
>
> *Mini-Bodnar* GPSDOs it was first clearly observed and quantified
> using a cross-correlation, matched filter analysis as it was 'within
> the noise'.
>
> 5.With the TID effect confirmed on the *Mini-Bodnar* via cross-
> the noise'.
>
> correlation the peak at 3300 seconds (55 minutes) in the Allan
> Deviation could confidently be ascribed to the TID.
>
> Gwyn
> G3ZIL
>
> On Sunday, July 13, 2025 at 5:15:41 AM UTC+1 terry....@noaa.gov
> <mailto:terry....@noaa.gov> wrote:
> Deviation could confidently be ascribed to the TID.
>
> Gwyn
> G3ZIL
>
> On Sunday, July 13, 2025 at 5:15:41 AM UTC+1 terry....@noaa.gov
>
> __
>>>> pswsnetwork.caps.ua.edu/observations/
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>>>> -- Please follow the HamSCI
>>>> Community Participation
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>>>>
>>>> -- Please follow the HamSCI
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>>>> <http://hamsci.org/hamsci-community>-
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>>>> MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com <http://40MW5PR13MB5464.namprd13.prod.outlook.com> <https://groups.google.com/d/msgid/hamsci/MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com?utm_medium=email&utm_source=footer> <https://groups.google.com/d/msgid/hamsci/MW5PR13MB54640ACDB6DB3CC81828F60BD04BA%40MW5PR13MB5464.namprd13.prod.outlook.com?utm_medium=email&utm_source=footer>.
>>>>
>>>>
>>>> --
>>>> ----
>>>> Phil Erickson
>>>> phil.e...@gmail.com
>>>>
>>>> -- Please follow the HamSCI Community Participation
>>>> Guidelines at
>>>> http://hamsci.org/hamsci-community-participation-guidelines
>>>> <http://hamsci.org/hamsci-community-participation-guidelines>.
>>>>
>>>> --
>>>> ----
>>>> Phil Erickson
>>>> phil.e...@gmail.com
>>>>
>>>> -- Please follow the HamSCI Community Participation
>>>> Guidelines at
>>>> http://hamsci.org/hamsci-community-participation-guidelines
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>>>> msgid/hamsci/22c2c7ed-0012-4c2a-ae81>-
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>>>> --
>>>> Please follow the HamSCI Community Participation Guidelines
>>>> at http:// hamsci.org/hamsci-community-participation-
>>>> --
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>>>> <https://groups.google.com/d/msgid/
>>>> hamsci/8e9c982e-6bfd-4ffd-8740-
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>>>> utm_medium=email&utm_source=footer> <https://
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>>>> utm_medium=email&utm_source=footer>.
>>>
>>> --
>>> Dr. Terry Bullett WØASP
>>> NOAA National Centers for Environmental Information (NOAA/NCEI)
>>> Cooperative Institute for Research in Environmental Sciences
>>> (CIRES)
>>> Terry....@noaa.gov 720-446-9775 <tel:(720)%20446-9775>
>>>
>>> --
>>> Dr. Terry Bullett WØASP
>>> NOAA National Centers for Environmental Information (NOAA/NCEI)
>>> Cooperative Institute for Research in Environmental Sciences
>>> (CIRES)
>>> (google voice) 978-337-9092 <tel:(978)%20337-9092> (cell)
>>> "Life is Complex. It has a Real part and an Imaginary part."
>>>
>>> --
>>> Please follow the HamSCI Community Participation Guidelines
>>> at http:// hamsci.org/hamsci-community-participation-
>>>
>>> --
>>> Please follow the HamSCI Community Participation Guidelines
>>> at http:// hamsci.org/hamsci-community-participation-
>>> guidelines <http://hamsci.org/hamsci-community-participation-
>>> guidelines> <http://hamsci.org/ hamsci-community-
>>> participation-guidelines> <http://hamsci.org/hamsci-
>>> guidelines> <http://hamsci.org/ hamsci-community-
>>> community-participation-guidelines>.
>>> ---
>>> You received this message because you are subscribed to the
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>>> msgid/ <https://groups.google.com/d/msgid/> hamsci/7caab4a8-
>>> Google Groups "HamSCI" group.
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>>> To view this discussion visit https://groups.google.com/d/
>>> b76d-436f-9032-8813139090d7%40noaa.gov <http://40noaa.gov>
>>> <https:// groups.google.com/d/msgid/hamsci/7caab4a8-
>>> b76d-436f-9032-8813139090d7%40noaa.gov?
>>> utm_medium=email&utm_source=footer> <https://
>>> groups.google.com/d/msgid/hamsci/7caab4a8-
>>> b76d-436f-9032-8813139090d7%40noaa.gov?
>>> utm_medium=email&utm_source=footer>.
>>
>
> --
> Dr. Terry Bullett WØASP
> NOAA National Centers for Environmental Information (NOAA/NCEI)
> Cooperative Institute for Research in Environmental Sciences (CIRES)
> Terry....@noaa.gov 720-446-9775 <tel:(720)%20446-9775> (google voice)978-337-9092 <tel:(978)%20337-9092> (cell)
>>
>
> --
> Dr. Terry Bullett WØASP
> NOAA National Centers for Environmental Information (NOAA/NCEI)
> Cooperative Institute for Research in Environmental Sciences (CIRES)
> "Life is Complex. It has a Real part and an Imaginary part."
>
> --
> Please follow the HamSCI Community Participation Guidelines at
> http://hamsci.org/hamsci-community-participation-guidelines <http://
>
> --
> Please follow the HamSCI Community Participation Guidelines at
> hamsci.org/hamsci-community-participation-guidelines>.
> ---
> You received this message because you are subscribed to the Google
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> hamsci/9f0647c0-5f76-4e0e-a07e-8b0a6270aaebn%40googlegroups.com
> Groups "HamSCI" group.
> To unsubscribe from this group and stop receiving emails from it,
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> a07e-8b0a6270aaebn%40googlegroups.com?
> utm_medium=email&utm_source=footer>.
>
> --
> Please follow the HamSCI Community Participation Guidelines at http://
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>
> --
> Please follow the HamSCI Community Participation Guidelines at http://
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> ---
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> ---
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