04/19/2022 Whistler Events!!

[Jonathan]

On April 19, Nathaniel and I were treated to some beautiful whistlers here in Northeast PA! The event detector detected 4 weak whistlers that were also detected at a VLF receiver in Virginia as well, so they had a large footprint. They also have a large dispersion measure too. Here are the spectrograms:

As you can see, they were definitely weak, but delectable. The event detector used Hough transform that looks for a the characteristic whistler curve. 

Speaking of whistlers with large footprints, here is a whistler with a footprint of over 900km received in Northeast PA, Virginia, and South Carolina! It has a dispersion measure of 69:

Jonathan

KC3EEY 

[Jonathan]

One of the allure of whistlers is actually listening to them! Attached
are movies I've made of the spectrograms and the event audio.

Jonathan
KC3EEY

On 4/29/22, Jonathan <emum...@gmail.com> wrote:
> On April 19, Nathaniel and I were treated to some beautiful whistlers here
> in Northeast PA! The event detector detected 4 weak whistlers that were
> also detected at a VLF receiver in Virginia as well, so they had a large
> footprint. They also have a large dispersion measure too. Here are the
> spectrograms:
>

> As you can see, they were definitely weak, but delectable. The event
> detector used Hough transform that looks for a the characteristic whistler
> curve.
>
> Speaking of whistlers with large footprints, here is a whistler with a
> footprint of over 900km received in Northeast PA, Virginia, and South
> Carolina! It has a dispersion measure of 69:
>

> Jonathan
> KC3EEY
>

[Dr. Nathaniel A. Frissell Ph.D.]

Hey, Jonathan! This is really great! Thank you!

I was on a journal club telecon with people from the NASA MSFC yesterday re-capping the HamSCI workshop, and your work came up quite a bit. They really liked it!

I'm looking forward to the results now that we have the grounding noise issue resolved.

73 Nathaniel W2NAF

[Robert McGwier]

Ahhh  I was going to ask if the ground loop/AC hum had been worked on.  The whistlers are audible and we would be able to agc them to loud if we could eliminate the equipment made hum. This will increase the usable dynamic range in the audio output. 

Nice stuff.  Easily seen in the spectrograms.

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Dr. Robert W McGwier, Ph.D.
Adjunct Faculty, Virginia Tech
ARDC Member of Board
N4HY: ARRL, TAPR, AMSAT, EARC, CSVHFS
Sky: AAVSO, Sky360, Auburn A.S., Skyscrapers

[Jonathan]

Hi Bob,

These whistlers were captured before the ground wire was removed, but during a period of low mains harmonics levels. Mains harmonics would vary in amplitude quite a bit, burying the spectrogram in noise one day and low enough another day where it is possible to detect natural radio signals. 

Their source was the residence, including all the wiring and loads inside. Pulling up the ground wire made a big difference, but now, the GPS receiver isn’t outputting PPS or communicating over serial, so I have to investigate that. 

Jonathan

KC3EEY 

[Dana Whitlow]

Hi Jonathan,

Would you perchance have any uncompressed audio recordings of whistlers,

such as in WAV format or similar?  I'd like to try my hand at removing as much

of the surrounding clutter as possible (in both time and freq domains) so as to

bring the whistler out clearly for my tired old ears, which have deteriorated

markedly in recent years.

Thanks,

Dana   K8YUM

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[Robert McGwier]

Great suggestion. If you want to compress, use lossless compression like flac.

Bob

N4HY

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[Jonathan]

Hi Dana,

These whistlers were detected before the ground wire was removed.

The files I attached in my original post are not AAC compressed audio
files. They are videos made with the spectrogram image still with the
AAC compressed audio track.

The event detector only reliably works with 48k or 32k sample rates
and I use 32k, which means that the event files only have a bandwidth
of 16 kHz. I have attached the wav files with a gain factor of 10 and
the original vt files that retain timestamping and without any gain
factor.

If you use vlfrx-tools, you can use this filtering scheme (with an
event file as an example):

vtfilter -h bs,f=150,w=300 -h hp,f=50,poles=3 -h lp,f=8000,poles=3 -h
bs,f=8200,w=900
1650355192.vt |
vtblank -a 25 -v -d0 -t20 -v |
vtfilter -a th=4,ul=10000 |
vtraw -g 10 -ow >
1650355192g10_filtered.wav

This includes two band stop filters and a 3-pole low and high pass
filter as well as a mains tracking filter with an upper limit of 10
kHz of mains harmonics to remove the scratchiness. Lastly, it uses a
sferic blanker to blank out any sferics and makes it easier on the
ears.

On a side note, sferic blanking is a tool that makes coherent VLF
amateur radio transmissions possible.

I'm interested in any results you obtain in filtering!

Jonathan
KC3EEY

On 5/4/22, Robert McGwier <rwmc...@gmail.com> wrote:
> Great suggestion. If you want to compress, use lossless compression like
> flac.
>
> Bob
> N4HY
>
>
> On Wed, May 4, 2022, 12:23 PM Dana Whitlow <k8yum...@gmail.com> wrote:
>
>> Hi Jonathan,
>>

>> Would you perchance have any *uncompressed* audio recordings of

>> https://groups.google.com/d/msgid/hamsci/CADHrwpf%3D%3D44NfGBtnDakn_fup6CJ6sjiwVgg%3DxDR-P7VyYkQZA%40mail.gmail.com
>> <https://groups.google.com/d/msgid/hamsci/CADHrwpf%3D%3D44NfGBtnDakn_fup6CJ6sjiwVgg%3DxDR-P7VyYkQZA%40mail.gmail.com?utm_medium=email&utm_source=footer>
>> .

>>
>
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