Ottimo documento sulle VLF e non solo

Tratto dal gruppo VLF su Yahoo un ottimo compendio teorico-pratico sulle VLF .

Non lasciatevi trarre in inganno dai formalismi matematici , ci sono le descrizioni e soprattutto grafici e formule finali per risolvere casi veramente pratici .

Non facile , ma basilare per arrivare a corrette valutazioni .

Sette anni di pensieri di un " guru" del settore ....  

VLF notes

Mon Apr 2, 2018 7:20 am (PDT) . Posted by:

"Paul"

I put together some notes covering various mathematical aspects
of VLF propagation and reception -

http://abelian.org/vlf/pn1214.pdf

I started this document in 2011, collecting bits and pieces that I've
found useful for signal processing, modeling, and so on. Today I got
around to making it presentable.

Paul Nicholson

Riceviamo i segnali delle Aurore Boreali

Paul Nicholson sul gruppo VLF di Yahoo segnala la ricezione di segnali provenienti dalle Aurore Boreali .
Piu' facile la ricezione ad alte latitudini .
Molto meno alle nostre .
In parallelo temporale ed in sequenza dall'alto in basso gli spettrogrammi delle stazioni di Tomorden , Bielefeld e Cumiana ( Renato Romero )

I segnali sono la strisciate orizzontali a forma di S tra 2 e 5 KHz .
Le strisciate verticali a larga banda sono invece ovviamente fulmini .

Correlation between meteors and VLF-ELF signals ?

As described in the publication at the link :
http://air-radiorama.blogspot.it/2014/02/meteor-counter-with-graves-radar.html
in cooperation with many people , and in particular with Paul Nicholson , after months of automatic collection of relevant selected time stamped events ,we have enough material for who would like to develop a study around .
The data of more than 40 days (538 Mb) with 1059 events are available as images at the link :
ftp://sidmonitor.for-more.biz/0zipped%20archive/

There are four images for each event :

 1) Raw spectrogram of the echo of the meteor

2) Time domain GPS time stamped and correlated strip chart of :

A) The demodulated meteor echo ( "ping" ) in CW in Turin - Italy 

B) The VLF survey in Cumiana-Italy

C) The VLF survey in Bielefeld -Germany

Peaks in B and C are typically supposed to be lightning strikes 

3) Echo spectrogram expanded in time for VHF and VLF-ELF with pallette for amplitude

4) Echo spectrogram expanded in time for VHF and VLF-ELF with pallette for amplitude with only two colours 

"Ascoltiamo" le tempeste Geomagnetiche con un Magnetometro a basso costo

Recentemente abbiamo aggiunto all' Osservatorio di Strada Valpiana -Torino , costruito con la collaborazione di : AIR, CSP, Fabrizio Francione , Paul Nicholson,  Renato Romero ed il sottoscritto , un magnetometro a basso costo (circa 25 Eu) :

http://www.speakesensors.com/PDF/detail.pdf

Ecco il primo "ascolto" di una tempesta geomagnetica e la sua correlazione con l'osservatorio professionale Svedese di Lycksele .

Per chi volesse approfondire il fenomeno che tra l'altro e' uno dei fenomeni che eccita le aurore boreali , fornisco un collegamento ad un documento di Whitham Reeve , che ritengo meraviglioso :

http://www.reeve.com/Documents/SAM/GeomagnetismTutorial.pdf

Meteor Counter with the GRAVES radar - Automatic study of correlation with VLF-ELF

A group composed from :

Fabrizio Francione
Paul Nicholson
Emanuele Pelicioli
Renato Romero
and me , with the help of AIR and CSP ( www.csp.it)
is setting an automatic  system to correlate the meteors events recorded from the VHF station of Strada Valpiana (Turin) with the VLF events recordered at the VLF station of Cumiana (Turin).

Some of the preliminary tests could be found here :

http://www.sidmonitor.net/gallery/station2.html

and on the following  images :

Translatlantic link in the Dream Bands

Paul Nicholson  is computing and thinking about  a transatlantic link at 8.6 kHz .

Message  from the Yahoo VLF Group :

Over 10dB difference between E/W and W/E signal
strengths: Summer  W/E 0.25ft, E/W 0.07fT.

I ran another LWPC prediction,

West to east (eg Arizona to Todmorden)
--------------------------------------

Winter http://abelian.org/lwpc/140110g.gif

The extra over-land distance reduces the signal level
by about an extra 20dB. Given about 6 hours of steady
propagation in winter, the signal might still be detectable
in a single 6 hour integration of 46uHz bandwidth.

Path is about 8000km.

Paul Nicholson

European Activity in the Dream Bands ( 6-9 kHz)

From the Yahoo VLF Group :

Amateur activity by DJ8WX

Tue Jan 28, 2014 2:43 pm (PST) . Posted by:

"Paul"

For several nights DJ8WX (Munsterdorf 53.8958N,9.54167E)
has been transmitting carrier at 8270.004 or 8270.005 Hz,
several hours each night with good phase stability.

http://abelian.org/vlf/fbins.shtml#p=1390942800&b=080&s=sp

Signal is nearly 30dB above noise in 35uHz bandwidth here in
Todmorden (range 762 km).

http://abelian.org/vlf/tmp/dj8wx.140127a.gif

This is a good target for your receivers. It might be
detectable in North America (East coast, or not too far inland)
given first rate reception. LWPC predicts optimum period for
integration (phase stable) is 23:00 to 07:00 UT.

Definitely a GPS timed receiver will be needed to dig this
signal out of the noise. Quite a challenge, an opportunity
not to be missed.

Paul Nicholson

Segnali VLF emessi dal bolide che ha colpito la Russia ?

Questa la relazione di Paul Nicholson sul gruppo VLF di Yahoo .
Uno dei tre osservatori impiegati per la triangolazione e' stato quello di Cumiana di Renato Romero .

Oggetto: Re: [VLF_Group] Re: Meteor Blazes Across Sky over Russia
Data: Sat, 16 Feb 2013 21:56:29 +0000
Mittente: Paul <paul@abelian.netcom.co.uk>
Rispondi-a: VLF_Group@yahoogroups.com
A: VLF_Group@yahoogroups.com


We had good recordings from the European receivers and the
analyser picked out 15 possible signals in the 25 seconds
leading up to the final flare.

Output of the analyser :

http://abelian.org/vlf/tmp/130215a.gif

Time axis is aligned so that 120 seconds is 03:20:31 which is
roughly the time of the final flare.

Each spike indicates a possible signal. The spikes at 108 and
118 seconds are weak calibration pulses, waveform and timing
simulated for a source at 55.05N,59.8E

I've looked carefully at all these hits and none are genuine,
they are a typical collection of chance alignments of sferics.

Approximate ranges of the receivers are

Todmorden: 3900km
Bielefeld: 3300km
Cumiana: 3800km

As an example, here is one of the false hits, occurring 21
seconds before the final flare and some 5 to 7 seconds before
the meteor became visible on cameras,

http://abelian.org/vlf/tmp/130215b.gif

The analyser has picked out the scruffy little pulse which
arrives at the center of this plot. It is barely above noise.
In these charts, the three signals are time shifted so that
a signal originating at 55.05N,59.8E will be aligned on the
time axis.

I'll keep the signals filed with all the other fireballs and
when the calculated track of the meteor is published I can
try again with the better coordinates. The software is being
improved so there's always a chance that later this or one of
the other 250 filed events will turn something up.

Paul Nicholson

Nulla sfugge agli appassionati ... Trasmissione a 26.0 kHz da Israele

Guardate un po' cosa sono risuciti a fare gli appassionati del VLF Group .
Captata una nuova emissione a 26.0 kHz con alcune stazioni automatiche gestite da altri appassionati , dotate di campione temporale GPS , hanno triangolato , cercato con Gooogle maps e trovato la installazione :
https://maps.google.com/maps?q=30.972274,35.097198&hl=en&ll=30.97174,35.098078&spn=0.010119,0.01929&num=1&t=k&z=16

Si possono notare due tralicci , i sistemi di radiali ed in particolare un dirigibile che potrebbe avere portato in quota un cavo per avere un' antenna efficiente a tale frequenza .

Di seguito il diagramma temporale dell' attivita' della stazione da parte dell' Osservatorio di Kiel , gestito dall'appassionato che ha effettuato la ricerca: Peter DF3LP .
E la sintesi delle triangolazioni di Paul Nicholson .