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<!doctype html><html data-theme=light lang=en xmlns=http://www.w3.org/1999/xhtml><head><meta charset=UTF-8><meta name=description><meta content="width=device-width,initial-scale=1" name=viewport><meta content=#FF7E3C name=theme-color><meta content=#CC5A26 media=(prefers-color-scheme:dark) name=theme-color><title>Sferics - Aron Petau</title><link href=https://aron.petau.net/project/sferics/ rel=canonical><link href=https://mastodon.online/@reprintedAron rel=me><meta content=@reprintedAron@mastodon.online name=fediverse:creator><link href=/favicon/favicon-96x96.png rel=icon sizes=96x96 type=image/png><link href=/favicon/favicon.svg rel=icon type=image/svg+xml><link rel="shortcut icon" href=/favicon/favicon.ico><link href=/favicon/apple-touch-icon.png rel=apple-touch-icon sizes=180x180><meta content="Aron Petau" name=apple-mobile-web-app-title><link href=/favicon/site.webmanifest rel=manifest><link crossorigin href=https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.7.2/css/all.min.css integrity=sha512-... referrerpolicy=no-referrer rel=stylesheet><link title="Aron Petau - RSS Feed" href=https://aron.petau.net/rss.xml rel=alternate type=application/rss+xml><link title="Aron Petau - Atom Feed" href=https://aron.petau.net/atom.xml rel=alternate type=application/atom+xml><style>:root{--accent-color:#ff7e3c}[data-theme=dark]{--accent-color:#cc5a26}@media (prefers-color-scheme:dark){:root:not([data-theme=light]){--accent-color:#cc5a26}}</style><link href=https://aron.petau.net/style.css rel=stylesheet><link href=https://aron.petau.net/css/timeline.css rel=stylesheet><link href=https://aron.petau.net/css/mermaid.css rel=stylesheet><link href=https://aron.petau.net/css/skills.css rel=stylesheet><link href=https://aron.petau.net/css/gallery.css rel=stylesheet><script defer src=https://aron.petau.net/closable.js></script><script defer src=https://aron.petau.net/copy-button.js></script><script data-goatcounter=https://awebsite.goatcounter.com/count defer src=https://aron.petau.net/count.js></script><script defer src=https://aron.petau.net/fuse.js></script><script defer src=https://aron.petau.net/search-fuse.js></script><script defer src=https://aron.petau.net/theme-switcher.js></script><script type=module>import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs';
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mermaid.initialize({ startOnLoad: true });</script><meta content="Aron Petau" property=og:site_name><meta content="Sferics - Aron Petau" property=og:title><meta content=https://aron.petau.net/project/sferics/ property=og:url><meta content="Hunting for the voice of lightning from thousands of kilometers away" property=og:description><meta content=https://aron.petau.net/card.png property=og:image><meta content=en_US property=og:locale><body><header id=site-nav><nav><a href=#main-content tabindex=0> Skip to Main Content </a><ul><li id=home><a href=https://aron.petau.net> <i class=icon></i>Aron Petau</a><li class=divider><li><a href=https://aron.petau.net/project/>Projects</a><li><a href=https://aron.petau.net/pages/contact/>Contact</a><li><a href=https://aron.petau.net/pages/cv/>CV</a><li><a href=https://aron.petau.net/pages/about/>About</a><li id=search><button class=circle id=search-toggle title=Search><i class=icon></i></button><li id=language-switcher><details class=closable><summary class=circle title=Language><i class=icon></i></summary> <ul><li><a href=https://aron.petau.net//de/project/sferics/ lang=de>Deutsch</a></ul></details><li id=theme-switcher><details class=closable><summary class=circle title=Theme><i class=icon></i></summary> <ul><li><button title="Switch to Light Theme" class=circle id=theme-light><i class=icon></i></button><li><button title="Switch to Dark Theme" class=circle id=theme-dark><i class=icon></i></button><li><button title="Use System Theme" class=circle id=theme-system><i class=icon></i></button></ul></details><li id=feed><details class=closable><summary class=circle title=Feed><i class=icon></i></summary> <ul><li><a href=https://aron.petau.net/rss.xml>RSS</a><li><a href=https://aron.petau.net/atom.xml>Atom</a></ul></details><li id=repo><a class=circle href=https://forgejo.petau.net/aron/awebsite title=Repository> <i class=icon></i> </a></ul></nav><div id=search-container><label class=visually-hidden for=search-bar>Search</label><input placeholder="Search for…" autocomplete=off disabled id=search-bar type=search><div id=search-results-container><div id=search-results></div></div></div></header><main id=main-content><article><div id=heading><p><small> <time datetime=" 2024-06-20T00:00:00+00:00">Published on June 20, 2024</time></small><h1>Sferics</h1><p><small><span>By Aron Petau</span><span> • </span><span>3 minutes read</span><span> • </span></small><ul class=tags><li><a class=tag href=https://aron.petau.net/tags/antenna/>antenna</a><li><a class=tag href=https://aron.petau.net/tags/electronics/>electronics</a><li><a class=tag href=https://aron.petau.net/tags/geosensing/>geosensing</a><li><a class=tag href=https://aron.petau.net/tags/lightning/>lightning</a><li><a class=tag href=https://aron.petau.net/tags/radio/>radio</a><li><a class=tag href=https://aron.petau.net/tags/sferics/>sferics</a><li><a class=tag href=https://aron.petau.net/tags/vlf/>vlf</a><li><a class=tag href=https://aron.petau.net/tags/university-of-the-arts-berlin/>university of the arts berlin</a></ul></div><div id=buttons-container><a title="Go to Top" href=#top id=go-to-top><i class=icon></i></a><a href="https://shareopenly.org/share/?url=https://aron.petau.net/project/sferics/&text=Hunting%20for%20the%20voice%20of%20lightning%20from%20thousands%20of%20kilometers%20away" id=share title=Share><i class=icon></i></a><a title="File an Issue" href=https://forgejo.petau.net/aron/awebsite/issues id=issue><i class=icon></i></a></div><h2 id=What_the_Hell_are_Sferics?>What the Hell are Sferics?</h2><blockquote><p>A radio atmospheric signal or sferic (sometimes also spelled "spheric") is a broadband electromagnetic impulse that occurs as a result of natural atmospheric lightning discharges. Sferics may propagate from their lightning source without major attenuation in the Earth–ionosphere waveguide, and can be received thousands of kilometres from their source.</blockquote><p><em>Source: <a href=https://en.wikipedia.org/wiki/Radio_atmospheric_signal>Wikipedia</a></em><h2 id=Why_Catch_Them?>Why Catch Them?</h2><p><a href=https://microsferics.com>Microsferics</a> is a fascinating reference project—a network of sferics antennas used to detect lightning strikes. Through triangulation (not unlike GPS mathematics), they can determine the more-or-less exact location of each strike. This proves useful for weather prediction and detecting forest fires, which are often caused by lightning.<p>When converted to audio, sferics frequencies fall within the audible range, making it possible to actually <em>listen</em> to lightning strikes. The sound is usually a crackling noise, though sometimes surprisingly melodic—reminiscent of a Geiger counter.<h3 id=The_Technical_Challenge>The Technical Challenge</h3><p>Sferics live in the VLF (Very Low Frequency) range, around 10 kHz—a problem for most radios not designed for such low frequencies. That's why we built our own antenna.<p>At 10 kHz, we're dealing with <em>insanely</em> large waves: a single wavelength stretches roughly 30 kilometers. This scale demands a sizable antenna. A special property of such massive waves is their tendency to reflect between the ionosphere and Earth's surface—effectively bouncing around the globe several times before absorption. This means we can pick up sferics from all over the world, even Australian lightning strikes!<p>Without proper triangulation math, we can't determine exact directions, but the "tweeks" we captured typically originate from at least 2,000 km away.<h2 id=The_Build>The Build</h2><p>We constructed several "long-loop" antennas—essentially a coil of wire with a capacitor at the end. A specific balun is needed (depending on wire length) to output an electrical signal via XLR cable.<p>Loosely following instructions from <a href=https://archive.org/details/exploringlightra00graf>Calvin R. Graf</a>, we built a 26-meter antenna looped multiple times around a wooden frame.<h2 id=The_Result>The Result</h2><p>We captured several hours of sferics recordings, which we're currently investigating for further potential.<h3 id=Listen_to_the_Lightning>Listen to the Lightning</h3><iframe allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowfullscreen class=youtube-embed referrerpolicy=strict-origin-when-cross-origin src=https://www.youtube-nocookie.com/embed/2YYPg_K3dI4></iframe><p>As you can hear, there's a noticeable 60 Hz ground buzz in the recording. This likely stems from improper grounding or our proximity to the bustling city. Still, it's surprising we achieved such clear results so close to Berlin. Let's see what the countryside yields!<div id=image-gallery><ul class=gallery><li class=gallery-item><a class=lightbox href=https://aron.petau.net/project/sferics/./sferics1.jpg target=_blank> <img alt="Listening to sferics at night" src=https://aron.petau.net/project/sferics/./sferics1.jpg> </a> <p class=caption>Night session capturing atmospheric signals</p><li class=gallery-item><a class=lightbox href=https://aron.petau.net/project/sferics/./sferics2.jpg target=_blank> <img alt="The Drachenberg location" src=https://aron.petau.net/project/sferics/./sferics2.jpg> </a> <p class=caption>Recording location at Drachenberg</p><li class=gallery-item><a class=lightbox href=https://aron.petau.net/project/sferics/./sferics3.jpg target=_blank> <img alt="The long-loop antenna" src=https://aron.petau.net/project/sferics/./sferics3.jpg> </a> <p class=caption>Our 26-meter VLF antenna setup</p></ul></div></article><hr><nav id=post-nav><a class="post-nav-item post-nav-prev" 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