{"version":"1.0","provider_name":"Johnson&#039;s Techworld","provider_url":"https:\/\/johnsonfrancis.org\/techworld","author_name":"Johnson Francis","author_url":"https:\/\/johnsonfrancis.org\/techworld\/author\/jf\/","title":"Extremely Low Frequency (ELF) Submarine Communication - Johnson&#039;s Techworld","type":"rich","width":600,"height":338,"html":"<blockquote class=\"wp-embedded-content\" data-secret=\"nZJh99aP4O\"><a href=\"https:\/\/johnsonfrancis.org\/techworld\/extremely-low-frequency-elf-submarine-communication\/\">Extremely Low Frequency (ELF) Submarine Communication<\/a><\/blockquote><iframe sandbox=\"allow-scripts\" security=\"restricted\" src=\"https:\/\/johnsonfrancis.org\/techworld\/extremely-low-frequency-elf-submarine-communication\/embed\/#?secret=nZJh99aP4O\" width=\"600\" height=\"338\" title=\"&#8220;Extremely Low Frequency (ELF) Submarine Communication&#8221; &#8212; Johnson&#039;s Techworld\" data-secret=\"nZJh99aP4O\" frameborder=\"0\" marginwidth=\"0\" marginheight=\"0\" scrolling=\"no\" class=\"wp-embedded-content\"><\/iframe><script>\n\/*! This file is auto-generated *\/\n!function(d,l){\"use strict\";l.querySelector&&d.addEventListener&&\"undefined\"!=typeof URL&&(d.wp=d.wp||{},d.wp.receiveEmbedMessage||(d.wp.receiveEmbedMessage=function(e){var t=e.data;if((t||t.secret||t.message||t.value)&&!\/[^a-zA-Z0-9]\/.test(t.secret)){for(var s,r,n,a=l.querySelectorAll('iframe[data-secret=\"'+t.secret+'\"]'),o=l.querySelectorAll('blockquote[data-secret=\"'+t.secret+'\"]'),c=new RegExp(\"^https?:$\",\"i\"),i=0;i<o.length;i++)o[i].style.display=\"none\";for(i=0;i<a.length;i++)s=a[i],e.source===s.contentWindow&&(s.removeAttribute(\"style\"),\"height\"===t.message?(1e3<(r=parseInt(t.value,10))?r=1e3:~~r<200&&(r=200),s.height=r):\"link\"===t.message&&(r=new URL(s.getAttribute(\"src\")),n=new URL(t.value),c.test(n.protocol))&&n.host===r.host&&l.activeElement===s&&(d.top.location.href=t.value))}},d.addEventListener(\"message\",d.wp.receiveEmbedMessage,!1),l.addEventListener(\"DOMContentLoaded\",function(){for(var e,t,s=l.querySelectorAll(\"iframe.wp-embedded-content\"),r=0;r<s.length;r++)(t=(e=s[r]).getAttribute(\"data-secret\"))||(t=Math.random().toString(36).substring(2,12),e.src+=\"#?secret=\"+t,e.setAttribute(\"data-secret\",t)),e.contentWindow.postMessage({message:\"ready\",secret:t},\"*\")},!1)))}(window,document);\n\/\/# sourceURL=https:\/\/johnsonfrancis.org\/techworld\/wp-includes\/js\/wp-embed.min.js\n<\/script>\n","thumbnail_url":"https:\/\/johnsonfrancis.org\/techworld\/wp-content\/uploads\/2026\/07\/Extremely-Low-Frequency-ELF-Submarine-Communication.jpg","thumbnail_width":1279,"thumbnail_height":718,"description":"Submarines are effectively shielded from standard radio frequencies by the high electrical conductivity of seawater. Normal RF signals attenuate and disappear within a few meters of the surface. Extremely Low Frequency (ELF) radio waves\u2014typically operating between 30 and 300 Hz\u2014are one of the only ways to penetrate hundreds of meters of ocean, allowing command authorities [&hellip;]"}