VLF solar flare monitor

[Julius Madey]

Did anyone see the article in the February IEEE Spectrum by David Schneider about building a simple VLF receiver for solar flare and gamma ray burst detection?

[Willard Maier]

I had not seen it, but thanks for posting. Interesting article!

-Bill  KG5RMJ

[Dustin Reyes]

I did (https://spectrum.ieee.org/detect-solar-flares-and-gamma-ray-bursts-for-less-than-100 in case anyone hasn't yet) - I'd be interested in hearing any thoughts on the approach; I also only just saw this on the hamsci site:

https://hamsci.org/publications/using-pvc-pipe-antenna-and-raspberry-pi-detect-vlf-natural-radio-eposter

-Dustin

On Sat, Feb 12, 2022 at 11:54 PM Julius Madey <hil...@fairpoint.net> wrote:

Did anyone see the article in the February IEEE Spectrum by David Schneider about building a simple VLF receiver for solar flare and gamma ray burst detection?

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[Gerald Creager]

I also saw this while looking at the IEEE Spectrum article and following links (not enough caffeine to focus just yet)... https://physicsopenlab.org/2020/05/07/vlf-receiver-for-sid-monitoring/

Capt Gerry Creager, CAP

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gocivilairpatrol.com

Southwest Region -- Civil Air Patrol  https://swrcap.com/

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[Marco Lisi]

I read the article. Some comments about it:

1. you don't necessarily need the external sound card. The author explains that it was required in his case to extend the sampling frequency above the 44 Ksamples/s usually provided by internal soundcards;
2. the external loop antenna is also a "nice to have" feature, but most probably a simple length of insulated copper wire connected to the mic pin of a TRRS connector would do it.

Marco, IZ0FNO

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Aerospace & Defense

[John Magliacane]

Moore Observatory in Brownsboro, Kentucky (USA) has been plotting received NAA (24 kHz) signal strength as an indication of solar flare activity for years using a very simple TRF receiver:

http://moondog.astro.louisville.edu/

NAA transmits FSK data with lots of ERP, so measuring the relative signal strength is easy.

For what it's worth, I have observed very similar effects at LF by plotting relative peak signal levels of WWVB at 60 kHz from New Jersey. The attached plot was made from the "control" data I gathered the day before the 2017 solar eclipse.


73 de John, KD2BD

[Khan Tran]

Morning All,

Thanks Dustin for the IEEE link. 

I would love to try this but don’t think it’s a good idea at my current location. 

73, Khan KE8QWB 

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[Jonathan]

Hi Jules,

What an awesome article! Thanks for letting me know about it! The link to it can be found here:

https://spectrum.ieee.org/detect-solar-flares-and-gamma-ray-bursts-for-less-than-100

My system captured that very SID in the article quite nicely! The UT day plot below:

At a little past 16:00 UT, the enhancement can clearly be seen and matched with the plot in the article. I was able to zoom in on the data and you can clearly see the temporal scale of the enhancement:

As you can see, the enhancement occurred within 5 minutes. This is a great example of a SID caused by a solar flare. 

Hi Dustin,

That was my capstone project when I was still a student in 2020. It was based on a system designed by the author of vlfrx-tools, the de-facto open source signal processing tool set for ULF/VLF signals, for an MIT study. It consists of a VLF antenna and preamp encased inside of a PVC pipe connected to a Raspberry Pi via a soundcard and a GPS timing receiver. vlfrx-tools runs on the Pi and does the capture, timestamping to UT, recording, and analysis of the ULF/VLF signals. It’s currently running right now and has been installed since this past December. Using a vlfrx-tools utility called vtsid, VLF transmitters can be monitored. I currently monitor NAA, NLK, and NAU. See above for a plot of the very SID that was mentioned in the article captured using my system.

To get started monitoring SIDs, I highly recommend following the article. It even has a good method for testing and verifying the loop’s resonance. You can use a PC/laptop soundcard or a good USB soundcard. If you want to get much more serious, get the Behringer UMC202HD USB soundcard which has a 192 kHz sample rate. For multichannel reception (E Field, E-W H Field, N-S H Field, GPS PPS), get the UMC404HD with 4-channel input at 192 kHz sample rate. Both of these USB soundcards are hard iron performers when it comes to serious VLF study, but to get started, simply follow the article.

For the software, you can use Spectrum Lab (in Windows) or vlfrx-tools (in Linux). Both require a good deal of reading, especially vlfrx-tools, however, it’s worth it and you’ll end up doing more than SID monitoring. If you attach a GPS PPS signal to one input of the soundcard, you can also record the phase of the VLF transmitter signal. If you are like me, you can use vlfrx-tools to detect whistlers and chorus, steric analysis, live listening, and detection of amateur signals in the “dreamer’s band” (below 9 kHz) and elsewhere.

I have been heavily interested in ULF/VLF band since 2013 with my primary interest being Natural Radio, VLF transmitter monitoring, and detection of amateur ULF/VLF signals and I’m very active in the VLF community.

Hi Marco,

You are correct on both points. For monitoring NAA and others, I recommend at least a 96 kHz sampling rate. The reason why he used a tuned loop is because it can filter out unwanted signals like mains hum and harmonics, which could overload the soundcard frontend and cause distortion. Using a very long wire has been done before, successfully, in this configuration, but there is that risk of overloading the frontend in certain environments.

Hi John,

As always, I really appreciate your replies. The Moore Observatory’s NAA receiver is really unique in that it produces a signal proportional to the signal level and a DAQ records the voltage. This was a clever way to do it before using a soundcard as a VLF SDR was mainstream. That is a really nice looking plot of WWVB, and yes, it certainly can be used to monitor SIDs. If you use a 192 kHz soundcard with Spectrum Lab or vlfrx-tools, you can have vtsid monitor WWVB. 


Hi Kahn,

The best way to know whether you can do it is giving it a try. You can use Spectrum Lab to see your spectrum and if local noise drowns out the VLF transmitter signals.

Jonathan

KC3EEY

On Feb 12, 2022, at 11:54 PM, Julius Madey <hil...@fairpoint.net> wrote:

> Did anyone see the article in the February IEEE Spectrum by David Schneider about building a simple VLF receiver for solar flare and gamma ray burst detection?
>

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[Dustin Reyes]

Thank you for all the advice and detail Jonathan! Definitely going to look into setting up my own receiver; my location isn't great noise-wise but hoping at least a few stations are regularly visible.

-Dustin

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[David Eckhardt]

For this purpose, does anyone have a recommendation for a PC sound card that does not contain frequency roll-offs at both the low end (30 Hz) and the high end (20+ kHz)?   I bought a "higher" end sound card (heaven forbid, it's classed as a "gaming" sound card $%^Y&*) which appeared per published specifications to not have built-in roll-offs.  However, on installing and testing it, I discovered the roll-offs were present.  Suggestions??

One does not need a VLF "receiver" (PC sound card) to monitor for Solar flares and other Solar emissions.  Any reasonable SW receiver that can receive 20 ± MHz (and above) can easily receive the increased noise floor caused by most solar emissions.  I have a receiver going 24/7/365 for that purpose.  Just an alternative to receiving and plotting the submarine comms.

Dave - WØLEV

    

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[Stephen Kangas]

Xonar Essence STX model card from Asus.  Initially targeted to the “audiophile” market for use in media servers, it has also been embraced by gamers due to its 5.1 surround capability and great price.  Since it does 192KHz sampling (at 24bit) the high end frequency response was measured by one reviewer as -3.5db at 90KHz but likely will go a bit beyond at the expense of increasing THD above the Nyquist point (95KHz; for any sound card, internal or external, you’ll want to look for at least 192KHz sampling rate or more to extend the high-end frequency response above 20-24KHz Nyquist point of the more common 44/48Khz sampling devices, but that is no guarantee that the freq reponse isn’t rolled off earlier from analog filtering).  I have one of these for use in my audio workstation work, and like it as being the best internal PCIe card yet and fantastic value at the price, but not as hi-end audio as some external DACs/ADCs costing $1-5K.  It does NOT do DC response, and the bench measured reviews I’ve seen show it -3.5db at less than 10Hz (one as low as 5), but at least it’s lower than your requested 30Hz.

https://www.stereophile.com/content/asus-xonar-essence-ststx-soundcards-measurements

The bit more expensive Xonar Phoebus sports an built-in headphone amp with plenty of power, but I haven’t found bench lab tests of its response, distortion, jitter, etc.; it may fill your bill, also.  The Xonar products are very well made using above-average components and internal board layer ground plane shielding.

 

Be aware that Asus provides drivers only for Windows OS; I haven’t tried using my Xonar with a linux machine and it’s possible no one has created a driver for tha.

 

Stephen W9SK

On Sat, Feb 12, 2022 at 8:54 PM Julius Madey <hil...@fairpoint.net> wrote:

Did anyone see the article in the February IEEE Spectrum by David Schneider about building a simple VLF receiver for solar flare and gamma ray burst detection?

[David G. McGaw]

You don't get increased distortion past the Nyquist frequency.  You get aliasing.  Be aware that a lot of ADCs are not adequately filtered to avoid aliasing around Nyquist - it is cheaper and more computationally efficient to use half-band filters, but it gives -3dB response at and some aliasing above Nyquist, where the response should be gone.  Some are also very droopy at the higher frequencies due to an inadequate number of filter taps.  These have been criteria for choosing an ADC for the VLF card for the TangerineSDR.

David N1HAC

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[Stephen Kangas]

Xonar Essence STX model card from Asus should be considered.  Initially targeted to the “audiophile” market for use in media servers, it has also been embraced by gamers due to its 5.1 surround capability and great price.  Since it does 192KHz sampling (at 24bit) the high end frequency response was measured by one reviewer as -3.5db at 90KHz but likely will go a bit beyond at the expense of increasing THD above the Nyquist point (95KHz; for any sound card, internal or external, you’ll want to look for at least 192KHz sampling rate or more to extend the high-end frequency response above 20-24KHz Nyquist point of the more common 44/48Khz sampling devices, but that is no guarantee that the freq reponse isn’t rolled off earlier from analog filtering).  I have one of these for use in my audio workstation work, and like it as being the best internal PCIe card yet and fantastic value at the price, but not as hi-end audio as some external DACs/ADCs costing $1-5K.  It does NOT do DC response, and the bench measured reviews I’ve seen show it -3.5db at less than 10Hz (one as low as 5), but at least it’s lower than your requested 30Hz.

https://www.stereophile.com/content/asus-xonar-essence-ststx-soundcards-measurements

The bit more expensive Xonar Phoebus sports an built-in headphone amp with plenty of power, but I haven’t found bench lab tests of its response, distortion, jitter, etc.; it may fill your bill, also.  The Xonar products are very well made using above-average components and internal board layer ground plane shielding.

 

Be aware that Asus provides drivers only for Windows OS; I haven’t tried using my Xonar with a linux machine and it’s possible no one has created a driver for tha.

 

Stephen W9SK

 

 

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[Stephen Kangas]

I beg to differ; aliasing is a form of distortion, and it contributes as harmonics to THD (Total Harmonic Distortion).  

There are many different forms of distortion components, which alter the original intended sound, aliasing being one of those.  Measuring those components in manner that distinguishes them requires equipment/techniques designed for the purpose, which you don't see often in "reviews", thus as an audiophile (and former design engineer) tend to favor reviews performed by competent engineers with lab equipment and associated know-how beyond the lab equipment that I use here.

Nonetheless, there are digital audio designs employ DSP filtering algorithms (eg, related to dithering) in combination with analog filtering to improve upon anti-aliasing without introducing additional phase shift distortion caused by multi-pole sharper cut-off analog filtering, something that audiophiles don't like.  

All of this distortion may be irrelevant to the goal of the article here, so FWIW YMMV; I'm simply responding to the OP's question about freq response with what may (or not be) a good candidate for his project (and the only card I personally know provides such extended response), and where alternatives with higher distortion, that includes aliasing distortion above the Nyquist freq, may be tolerable anyway.

Stephen W9SK

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[David G. McGaw]

Sorry to argue, but aliasing is NOT harmonically related.  It is not distortion.  It is noise and contributes to that portion of THD+N (Total Harmonic Distortion plus Noise).  BTW, I have designed and supported pro-level analog and digital audio systems.

David N1HAC

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[Stephen Kangas]

Sorry David; we'll just have to agree to disagree.  I, too, have professionally designed both analog and digital audio equipment in the past for manufacturers and studios (and still do for myself as an audiophile pursuing the envelope, which is why I have in-house owned and rented lab equipment), and you'll find that my electronics engineering peers would also find your position on this out of the norm.  It's hopefully still a free nation for anyone to hold their own unique or minority-shared beliefs, so I'll offer no further comments about this here.

Respectfully, Stephen W9SK, BSEE, MSCSIA

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[David Eckhardt]

I'm well aware of the half-octave filtering technique.  I just wish the Tangerine SDR came with a bit of a lower price tag and didn't require me to do the coding (programming) to use it as I need.  I'm an old fossil analog / RF type and intentionally avoided programming in my career.  Early on in my career when the company was still giving me all the opportunities it offered a newbie (when corporate America still cared about their employees), I became very good at machine language programming.  That experience for three years taught me I am happier with the soldering pen and good selection (HP) RF test equipment.  Also, I have no need or requirement for the transmitter which, I believe, is part of the Tangerine SDR.  Please correct me if I'm wrong.

The sound card I bought to replace the rather numb unit on the motherboard was/is a Xonar Sound Blaster Z-series (SBX Prostudio) with an advertised sampling rate of 192 kHz.  I figured with that, the Nyquist would be roughly 2X that or approaching 400 kHz.  WRONG.....  Once I installed it and noticed using SpectrumLab that anything much above 23 kHz was gone - nonexistent.  Same for below 30 Hz   So, I connected my audio signal generator to the line input.  Yep.....sure enough, brick wall roll-off at 30 Hz and 22 kHz which I presume is embodied in FW.  It's useless to me for setting up the ELF SID detection or other more esoteric applications I had / have in mind.  I need a sound card with 192 kHz sampling rate and NO input or otherwise frequency limitations up to Nyquist.

Dave - WØLEV  

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[David G. McGaw]

The Nyquist frequency, the theoretical maximum frequency able to be sampled or reproduced (which is not actually achievable in real systems), is 1/2 the sample rate, not twice.  Nyquist for 192kHz sampling is 96kHz.  Practically, a good system may be able to reach 90kHz with a 6 kHz transition band.  Many, as you have seen, do not even come close.

TangerineSDR will be receive-only at first.  The transmitter will be optional.

Just an aside, for digital audio we are still not up to the standards of Rupert Neve, who insisted that all his mixing boards be designed for 200kHz response, saying he could hear the difference.  I believe him.  We used to say 100kHz was a minimum requirement for Hi-Fi, before digital audio lowered people's expectations.

David N1HAC

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[Dana Whitlow]

I believe the reason for a high sample rate combined with a rather soft transition band is to 

improve phase linearity in the anti-alias filter, not really to extend the high frequency

response.

Dana

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[Jonathan]

Dustin,

Even in my backyard that was bathed in 60 Hz hum and harmonics, as
well as noisy switchers, I was able to pick up NAA with ease. A tuned
loop will make it even easier.

Dave,

That roll off is often a function of input stages of the soundcards.
Unfortunately, the best way to know for sure is experimentation. In
most cases, the roll off isn't much of an issue unless you are
interested in broadband reception of ELF/ULF/VLF. Below 30 Hz, the
Schumann resonances are present. Do you have reception interests in
the ELF/ULF/VLF band? I recommend the Behringer UMC202/404HD USB audio
interfaces or the Asus Xonar D1.

Monitoring VLF transmitters has the benefit of telling you the
ionosphere has been perturbed in other regions of the world along the
path of the VLF transmitter. One VLF receiver and soundcard can
capture wideband spectrum and actively monitor both amplitude and
phase (phase with a GPS reference). It can be easier to tell a SID on
the VLF transmitter because there is usually enhancement where the
effect is opposite in HF and harder to verify.

Hi Stephen,

The best Xonar card is the Xonar D1. It's PCI, but has been tested for
purposes of VLF reception. More information can be found at
https://www.n4vlf.net/vlfrx.html#Sound_Cards along with some
commentary of the newer Xonar cards. It really comes down to
experimentation. The Xonar D1 is supported in ALSA and OSS under Linux
and can be used with vlfrx-tools.

Jonathan
KC3EEY

> To view this discussion on the web visit https://groups.google.com/d/msgid/hamsci/086c01d821d5%24beb05f10%243c111d30%24%40kangas.com.

[Jonathan]

Dave,

See my other response in the original thread. I recommend the Asus
Xonar D1 or the Behringer UMC202HD or UMC404HD. Both work in Linux
with ALSA and can be used with vlfrx-tools or Spectrum Lab.

The Tangerine SDR will feature a VLF Module called the Whistler
Catcher for use with broadband VLF reception and will replace the PC
soundcard with GPS timestamping, however, it won't be ready for a
while. I'm spearheading the Whistler Catcher, so the biggest challenge
right now is implementing what needs to be done in the FPGA.

For now, to get started and learn VLF, you can use a soundcard and
feed a GPS PPS pulse into one of the channels for timestamped
broadband VLF reception that can be processed with many of the tools
in vlfrx-tools or Spectrum Lab. The system I use is a VLF receiver
with Raspberry Pi running vlfrx-tools.

Jonathan
KC3EEY

>>> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.stereophile.com%2Fcontent%2Fasus-xonar-essence-ststx-soundcards-measurements&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C3b8591f65e4b4db2f17908d9f00bf6c1%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637804756456010088%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=2m03BNpiFlCBYDoaldQyaBi%2BVyutBHS8d9%2Bl3w03rl8%3D&reserved=0>

>>>
>>> The bit more expensive Xonar Phoebus sports an built-in headphone amp
>>> with plenty of power, but I haven’t found bench lab tests of its
>>> response,
>>> distortion, jitter, etc.; it may fill your bill, also. The Xonar
>>> products
>>> are very well made using above-average components and internal board
>>> layer
>>> ground plane shielding.
>>>
>>>
>>>
>>> Be aware that Asus provides drivers only for Windows OS; I haven’t tried
>>> using my Xonar with a linux machine and it’s possible no one has created
>>> a
>>> driver for tha.
>>>
>>>
>>>
>>> Stephen W9SK
>>>
>>> On Sat, Feb 12, 2022 at 8:54 PM Julius Madey <hil...@fairpoint.net>
>>> wrote:
>>>
>>>> Did anyone see the article in the February IEEE Spectrum by David
>>>> Schneider about building a simple VLF receiver for solar flare and
>>>> gamma
>>>> ray burst detection?
>>>>
>>>> --
>>>> Please follow the HamSCI Community Participation Guidelines at
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>>>> <https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fhamsci.org%2Fhamsci-community-participation-guidelines&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C3b8591f65e4b4db2f17908d9f00bf6c1%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637804756456010088%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Xh8Vw%2BwGRoGpOzzYXALsj73Ii05v7vr8vCIEMTH8eLM%3D&reserved=0>
>>>> .

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>>>> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgroups.google.com%2Fd%2Fmsgid%2Fhamsci%2F0bb5b940-2fe0-3d25-9a11-a38a0b50840e%2540fairpoint.net%3Futm_medium%3Demail%26utm_source%3Dfooter&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C3b8591f65e4b4db2f17908d9f00bf6c1%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637804756456010088%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=RoQ9KPOdpdJ%2Bx%2B%2F1%2BFCSt7PCp8BdxpgjbOzA3cuVceE%3D&reserved=0>
>>>> .

>>>>
>>> --
>>> Please follow the HamSCI Community Participation Guidelines at
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>>> <https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fhamsci.org%2Fhamsci-community-participation-guidelines&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C3b8591f65e4b4db2f17908d9f00bf6c1%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637804756456010088%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Xh8Vw%2BwGRoGpOzzYXALsj73Ii05v7vr8vCIEMTH8eLM%3D&reserved=0>
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>>> .

>>>
>>>
>>> --
>>> Please follow the HamSCI Community Participation Guidelines at
>>> http://hamsci.org/hamsci-community-participation-guidelines

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>>> .

>>> ---
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>>> .
>>>
>>
>>
>> --
>> *Dave - WØLEV*
>> *Just Let Darwin Work*

>>
>> --
>> Please follow the HamSCI Community Participation Guidelines at
>> http://hamsci.org/hamsci-community-participation-guidelines

>> <https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fhamsci.org%2Fhamsci-community-participation-guidelines&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C3b8591f65e4b4db2f17908d9f00bf6c1%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637804756456010088%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Xh8Vw%2BwGRoGpOzzYXALsj73Ii05v7vr8vCIEMTH8eLM%3D&reserved=0>
>> .

>> ---
>> You received this message because you are subscribed to the Google Groups
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>> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgroups.google.com%2Fd%2Fmsgid%2Fhamsci%2FCAODdWWFRyfNiP5SZwNKoRc0VjBVH9vHq5GopC5MvbqXp3_mLFQ%2540mail.gmail.com%3Futm_medium%3Demail%26utm_source%3Dfooter&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C3b8591f65e4b4db2f17908d9f00bf6c1%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637804756456010088%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=TLK1CZ6NCDTMTblWIpcNlE%2FcWiJbeSvuPNsNf35KtOA%3D&reserved=0>
>> .

>>
>>
>> --
>> Please follow the HamSCI Community Participation Guidelines at
>> http://hamsci.org/hamsci-community-participation-guidelines.
>> ---
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>> To unsubscribe from this group and stop receiving emails from it, send an
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>> .

>>
>
> --
> Please follow the HamSCI Community Participation Guidelines at
> http://hamsci.org/hamsci-community-participation-guidelines.
> ---
> You received this message because you are subscribed to the Google Groups
> "HamSCI" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to hamsci+un...@googlegroups.com.
> To view this discussion on the web visit

> https://groups.google.com/d/msgid/hamsci/CADHrwpfK8Z_Mk7cKGLKrcqshmZeWrAdj8RkXm0-sx7yfHbyGFg%40mail.gmail.com.
>