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tuning</span> </div> </a> <ul id="toc-Dynamic_antenna_tuning-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-VLF_receiving_antennas" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#VLF_receiving_antennas"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>VLF receiving antennas</span> </div> </a> <ul id="toc-VLF_receiving_antennas-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Modulation" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Modulation"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Modulation</span> </div> </a> <ul id="toc-Modulation-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Applications" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Applications"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Applications</span> </div> </a> <button aria-controls="toc-Applications-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Applications subsection</span> </button> <ul id="toc-Applications-sublist" class="vector-toc-list"> <li id="toc-Early_wireless_telegraphy" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Early_wireless_telegraphy"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>Early wireless telegraphy</span> </div> </a> <ul id="toc-Early_wireless_telegraphy-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Navigation_beacons_and_time_signals" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Navigation_beacons_and_time_signals"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>Navigation beacons and time signals</span> </div> </a> <ul id="toc-Navigation_beacons_and_time_signals-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Geophysical_and_atmospheric_measurement" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Geophysical_and_atmospheric_measurement"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.3</span> <span>Geophysical and atmospheric measurement</span> </div> </a> <ul id="toc-Geophysical_and_atmospheric_measurement-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mine_communication_systems" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mine_communication_systems"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.4</span> <span>Mine communication systems</span> </div> </a> <ul id="toc-Mine_communication_systems-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Military_communications" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Military_communications"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.5</span> <span>Military communications</span> </div> </a> <ul id="toc-Military_communications-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Amateur_use" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Amateur_use"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Amateur use</span> </div> </a> <button aria-controls="toc-Amateur_use-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Amateur use subsection</span> </button> <ul id="toc-Amateur_use-sublist" class="vector-toc-list"> <li id="toc-Amateur_equipment" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Amateur_equipment"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.1</span> <span>Amateur equipment</span> </div> </a> <ul id="toc-Amateur_equipment-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-PC_based_reception" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#PC_based_reception"> <div class="vector-toc-text"> <span class="vector-toc-numb">5.2</span> <span>PC based reception</span> </div> </a> <ul id="toc-PC_based_reception-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-List_of_VLF_transmissions" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#List_of_VLF_transmissions"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>List of VLF transmissions</span> </div> </a> <ul id="toc-List_of_VLF_transmissions-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Further_reading" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Further_reading"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Further reading</span> </div> </a> <ul id="toc-Further_reading-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet 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Available in 27 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-27" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">27 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AA%D8%B1%D8%AF%D8%AF_%D8%B4%D8%AF%D9%8A%D8%AF_%D8%A7%D9%84%D8%A7%D9%86%D8%AE%D9%81%D8%A7%D8%B6" title="تردد شديد الانخفاض – Arabic" lang="ar" hreflang="ar" data-title="تردد شديد الانخفاض" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/VLF" title="VLF – Catalan" lang="ca" hreflang="ca" data-title="VLF" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/VLF" title="VLF – Danish" lang="da" hreflang="da" data-title="VLF" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/L%C3%A4ngstwelle" title="Längstwelle – German" lang="de" hreflang="de" data-title="Längstwelle" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%A5%CF%80%CE%B5%CF%81%CE%BC%CE%B1%CE%BA%CF%81%CE%AC_%CE%BA%CF%8D%CE%BC%CE%B1%CF%84%CE%B1" title="Υπερμακρά κύματα – Greek" lang="el" hreflang="el" data-title="Υπερμακρά κύματα" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Frecuencia_muy_baja" title="Frecuencia muy baja – Spanish" lang="es" hreflang="es" data-title="Frecuencia muy baja" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A8%D8%B3%D8%A7%D9%85%D8%AF_%D8%A8%D8%B3%DB%8C%D8%A7%D8%B1%D9%BE%D8%A7%DB%8C%DB%8C%D9%86" title="بسامد بسیارپایین – Persian" lang="fa" hreflang="fa" data-title="بسامد بسیارپایین" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Tr%C3%A8s_basse_fr%C3%A9quence" title="Très basse fréquence – French" lang="fr" hreflang="fr" data-title="Très basse fréquence" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%B4%88%EC%A0%80%EC%A3%BC%ED%8C%8C" title="초저주파 – Korean" lang="ko" hreflang="ko" data-title="초저주파" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D4%B3%D5%A5%D6%80%D5%A5%D6%80%D5%AF%D5%A1%D6%80_%D5%A1%D5%AC%D5%AB%D6%84%D5%B6%D5%A5%D6%80" title="Գերերկար ալիքներ – Armenian" lang="hy" hreflang="hy" data-title="Գերերկար ալիքներ" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%85%E0%A4%A4%E0%A4%BF_%E0%A4%A8%E0%A4%BF%E0%A4%AE%E0%A5%8D%E0%A4%A8_%E0%A4%86%E0%A4%B5%E0%A5%83%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF_(VLF)" title="अति निम्न आवृत्ति (VLF) – Hindi" lang="hi" hreflang="hi" data-title="अति निम्न आवृत्ति (VLF)" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Frekuensi_sangat_rendah" title="Frekuensi sangat rendah – Indonesian" lang="id" hreflang="id" data-title="Frekuensi sangat rendah" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Very_low_frequency" title="Very low frequency – Italian" lang="it" hreflang="it" data-title="Very low frequency" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Very_low_frequency" title="Very low frequency – Dutch" lang="nl" hreflang="nl" data-title="Very low frequency" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E8%B6%85%E9%95%B7%E6%B3%A2" title="超長波 – Japanese" lang="ja" hreflang="ja" data-title="超長波" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Veldig_lav_frekvens" title="Veldig lav frekvens – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Veldig lav frekvens" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Veldig_l%C3%A5g_frekvens" title="Veldig låg frekvens – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Veldig låg frekvens" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Fale_bardzo_d%C5%82ugie" title="Fale bardzo długie – Polish" lang="pl" hreflang="pl" data-title="Fale bardzo długie" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Frequ%C3%AAncia_muito_baixa" title="Frequência muito baixa – Portuguese" lang="pt" hreflang="pt" data-title="Frequência muito baixa" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%A1%D0%B2%D0%B5%D1%80%D1%85%D0%B4%D0%BB%D0%B8%D0%BD%D0%BD%D1%8B%D0%B5_%D0%B2%D0%BE%D0%BB%D0%BD%D1%8B" title="Сверхдлинные волны – Russian" lang="ru" hreflang="ru" data-title="Сверхдлинные волны" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/VLF_(taajuusalue)" title="VLF (taajuusalue) – Finnish" lang="fi" hreflang="fi" data-title="VLF (taajuusalue)" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/V%C3%A4ldigt_l%C3%A5g_frekvens" title="Väldigt låg frekvens – Swedish" lang="sv" hreflang="sv" data-title="Väldigt låg frekvens" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/%C3%87ok_d%C3%BC%C5%9F%C3%BCk_frekans" title="Çok düşük frekans – Turkish" lang="tr" hreflang="tr" data-title="Çok düşük frekans" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9D%D0%B0%D0%B4%D0%B4%D0%BE%D0%B2%D0%B3%D1%96_%D1%80%D0%B0%D0%B4%D1%96%D0%BE%D1%85%D0%B2%D0%B8%D0%BB%D1%96" title="Наддовгі радіохвилі – Ukrainian" lang="uk" hreflang="uk" data-title="Наддовгі радіохвилі" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vec mw-list-item"><a href="https://vec.wikipedia.org/wiki/Very_low_frequency" title="Very low frequency – Venetian" lang="vec" hreflang="vec" data-title="Very low frequency" data-language-autonym="Vèneto" data-language-local-name="Venetian" class="interlanguage-link-target"><span>Vèneto</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/T%E1%BA%A7n_s%E1%BB%91_r%E1%BA%A5t_th%E1%BA%A5p" title="Tần số rất thấp – Vietnamese" lang="vi" hreflang="vi" data-title="Tần số rất thấp" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E7%94%9A%E4%BD%8E%E9%A2%91" title="甚低频 – Chinese" lang="zh" hreflang="zh" data-title="甚低频" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q549933#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div 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div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"VLF" redirects here. For the car company, see <a href="/wiki/VLF_Automotive" title="VLF Automotive">VLF Automotive</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox hproduct"><caption class="infobox-title fn" style="padding-bottom:0.2em;"><span class="fn">Very low frequency</span></caption><tbody><tr><th scope="row" class="infobox-label" style="padding-top:0.15em;padding-right:1.0em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Frequency range</div></th><td class="infobox-data"><span class="nowrap">3–30 <a href="/wiki/KHz" class="mw-redirect" title="KHz">kHz</a></span></td></tr><tr><th scope="row" class="infobox-label" style="padding-top:0.15em;padding-right:1.0em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Wavelength range</div></th><td class="infobox-data"><span class="nowrap">100-10 km</span></td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output 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rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><table class="sidebar nomobile nowraplinks"><tbody><tr><th class="sidebar-title"><a href="/wiki/Radio_spectrum" title="Radio spectrum">Radio bands</a></th></tr><tr><th class="sidebar-heading" style="background:#ddddff;"> <a href="/wiki/ITU_radio_bands" class="mw-redirect" title="ITU radio bands">ITU </a></th></tr><tr><td class="sidebar-content" style="padding-top:0.2em; padding-bottom:0.6em;"> <table style="margin:0 auto;text-align:left;"><tbody><tr style="vertical-align:top"><td style="padding-right:1.0em;;"> <a href="/wiki/Extremely_low_frequency" title="Extremely low frequency">1 (ELF)</a></td><td style="padding-right:1.0em;;"> <a href="/wiki/Super_low_frequency" title="Super low frequency">2 (SLF)</a></td><td style="padding-right:1.0em;;"> <a href="/wiki/Ultra_low_frequency" title="Ultra low frequency">3 (ULF)</a></td><td style="padding-right:1.0em;;padding-right:0;"> <a class="mw-selflink selflink">4 (VLF)</a></td></tr><tr style="vertical-align:top"><td style="padding-right:1.0em;;"> <a href="/wiki/Low_frequency" title="Low frequency">5 (LF)</a></td><td style="padding-right:1.0em;;"> <a href="/wiki/Medium_frequency" title="Medium frequency">6 (MF)</a></td><td style="padding-right:1.0em;;"> <a href="/wiki/High_frequency" title="High frequency">7 (HF)</a></td><td style="padding-right:1.0em;;padding-right:0;"> <a href="/wiki/Very_high_frequency" title="Very high frequency">8 (VHF)</a></td></tr><tr style="vertical-align:top"><td style="padding-right:1.0em;;"> <a href="/wiki/Ultra_high_frequency" title="Ultra high frequency">9 (UHF)</a></td><td style="padding-right:1.0em;;"> <a href="/wiki/Super_high_frequency" title="Super high frequency">10 (SHF)</a></td><td style="padding-right:1.0em;;"> <a href="/wiki/Extremely_high_frequency" title="Extremely high frequency">11 (EHF)</a></td><td style="padding-right:1.0em;;padding-right:0;"> <a href="/wiki/Terahertz_radiation" title="Terahertz radiation">12 (THF)</a></td></tr></tbody></table></td> </tr><tr><th class="sidebar-heading" style="background:#ddddff;"> <a href="/wiki/NATO_radio_bands" class="mw-redirect" title="NATO radio bands">EU / NATO / US ECM </a></th></tr><tr><td class="sidebar-content" style="padding-top:0.2em; padding-bottom:0.6em;"> <div class="hlist"> <ul><li><a href="/wiki/A_band_(NATO)" title="A band (NATO)">A</a></li> <li><a href="/wiki/B_band_(NATO)" title="B band (NATO)">B</a></li> <li><a href="/wiki/C_band_(NATO)" title="C band (NATO)">C</a></li> <li><a href="/wiki/D_band_(NATO)" title="D band (NATO)">D</a></li> <li><a href="/wiki/E_band_(NATO)" title="E band (NATO)">E</a></li> <li><a href="/wiki/F_band_(NATO)" title="F band (NATO)">F</a></li> <li><a href="/wiki/G_band_(NATO)" title="G band (NATO)">G</a></li> <li><a href="/wiki/H_band_(NATO)" title="H band (NATO)">H</a></li> <li><a href="/wiki/I_band_(NATO)" title="I band (NATO)">I</a></li> <li><a href="/wiki/J_band_(NATO)" title="J band (NATO)">J</a></li> <li><a href="/wiki/K_band_(NATO)" title="K band (NATO)">K</a></li> <li><a href="/wiki/L_band_(NATO)" title="L band (NATO)">L</a></li> <li><a href="/wiki/M_band_(NATO)" title="M band (NATO)">M</a></li> <li><a href="/wiki/N_band_(NATO)" title="N band (NATO)">N</a></li></ul> </div></td> </tr><tr><th class="sidebar-heading" style="background:#ddddff;"> <a href="/wiki/Radio_spectrum#IEEE" title="Radio spectrum">IEEE </a></th></tr><tr><td class="sidebar-content" style="padding-top:0.2em; padding-bottom:0.6em;"> <div class="hlist"> <ul><li><a href="/wiki/High_frequency" title="High frequency">HF</a></li> <li><a href="/wiki/Very_high_frequency" title="Very high frequency">VHF</a></li> <li><a href="/wiki/Ultra_high_frequency" title="Ultra high frequency">UHF</a></li> <li><a href="/wiki/L_band" title="L band">L</a></li> <li><a href="/wiki/S_band" title="S band">S</a></li> <li><a href="/wiki/C_band_(IEEE)" title="C band (IEEE)">C</a></li> <li><a href="/wiki/X_band" title="X band">X</a></li> <li><a href="/wiki/Ku_band" title="Ku band">K<sub>u</sub></a></li> <li><a href="/wiki/K_band_(IEEE)" title="K band (IEEE)">K</a></li> <li><a href="/wiki/Ka_band" title="Ka band">K<sub>a</sub></a></li> <li><a href="/wiki/V_band" title="V band">V</a></li> <li><a href="/wiki/W_band" title="W band">W</a></li> <li><a href="/wiki/Extremely_high_frequency" title="Extremely high frequency">mm</a></li></ul> </div></td> </tr><tr><th class="sidebar-heading" style="background:#ddddff;"> Other TV and radio</th></tr><tr><td class="sidebar-content" style="padding-top:0.2em; padding-bottom:0.6em;"> <div class="hlist"> <ul><li><a href="/wiki/Band_I" title="Band I">I</a></li> <li><a href="/wiki/Band_II" title="Band II">II</a></li> <li><a href="/wiki/Band_III" title="Band III">III</a></li> <li><a href="/wiki/Band_IV" title="Band IV">IV</a></li> <li><a href="/wiki/Band_V" title="Band V">V</a></li> <li><a href="/wiki/Band_VI" title="Band VI">VI</a></li></ul> </div></td> </tr><tr><td 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4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Radio_bands_sidebar" title="Template:Radio bands sidebar"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Radio_bands_sidebar" title="Template talk:Radio bands sidebar"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Radio_bands_sidebar" title="Special:EditPage/Template:Radio bands sidebar"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table> <figure typeof="mw:File/Thumb"><a href="/wiki/File:VLFatPalmer.JPG" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/VLFatPalmer.JPG/236px-VLFatPalmer.JPG" decoding="async" width="236" height="177" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/VLFatPalmer.JPG/354px-VLFatPalmer.JPG 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2d/VLFatPalmer.JPG/472px-VLFatPalmer.JPG 2x" data-file-width="856" data-file-height="642" /></a><figcaption>A VLF receiving antenna at <a href="/wiki/Palmer_Station" title="Palmer Station">Palmer Station</a>, Antarctica, operated by <a href="/wiki/Stanford_University" title="Stanford University">Stanford University</a> </figcaption></figure> <p><b>Very low frequency</b> or <b>VLF</b> is the <a href="/wiki/International_Telecommunication_Union" title="International Telecommunication Union">ITU</a> designation<sup id="cite_ref-ITU_Nomenclature_1-0" class="reference"><a href="#cite_note-ITU_Nomenclature-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> for <a href="/wiki/Radio_frequency" title="Radio frequency">radio frequencies</a> (RF) in the range of 3–30 <a href="/wiki/KHz" class="mw-redirect" title="KHz">kHz</a>, corresponding to <a href="/wiki/Wavelength" title="Wavelength">wavelengths</a> from 100 to 10 km, respectively. The band is also known as the <b>myriameter band</b> or <b>myriameter wave</b> as the wavelengths range from one to ten <a href="/wiki/Myriameter" class="mw-redirect" title="Myriameter">myriameters</a> (an obsolete metric unit equal to 10 kilometers). Due to its limited <a href="/wiki/Bandwidth_(signal_processing)" title="Bandwidth (signal processing)">bandwidth</a>, <a href="/wiki/Audio_signal" title="Audio signal">audio</a> (voice) transmission is highly impractical in this band, and therefore only low <a href="/wiki/Data_signaling_rate" title="Data signaling rate">data rate</a> coded signals are used. The VLF band is used for a few <a href="/wiki/Radio_navigation" title="Radio navigation">radio navigation</a> services, government <a href="/wiki/Time_signal" title="Time signal">time radio stations</a> (broadcasting time signals to set <a href="/wiki/Radio_clock" title="Radio clock">radio clocks</a>) and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for <a href="/wiki/Military_communication" class="mw-redirect" title="Military communication">military communication</a> with <a href="/wiki/Submarine" title="Submarine">submarines</a>. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Propagation_characteristics">Propagation characteristics</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=1" title="Edit section: Propagation characteristics"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Because of their long wavelengths, VLF radio waves can <a href="/wiki/Diffraction" title="Diffraction">diffract</a> around large obstacles and so are not blocked by mountain ranges, and can propagate as <a href="/wiki/Ground_wave" title="Ground wave">ground waves</a> following the curvature of the Earth and so are not limited by the horizon. Ground waves are absorbed by the resistance of the Earth and are less important beyond several hundred to a thousand kilometres/miles, and the main mode of long-distance propagation is an <a href="/wiki/Earth-ionosphere_waveguide" class="mw-redirect" title="Earth-ionosphere waveguide">Earth-ionosphere waveguide</a> mechanism.<sup id="cite_ref-Hunsucker_2-0" class="reference"><a href="#cite_note-Hunsucker-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> The Earth is surrounded by a conductive layer of <a href="/wiki/Electron" title="Electron">electrons</a> and <a href="/wiki/Ion" title="Ion">ions</a> in the upper atmosphere at the bottom of the <a href="/wiki/Ionosphere" title="Ionosphere">ionosphere</a> called the <a href="/wiki/D_layer" class="mw-redirect" title="D layer">D layer</a> at 60–90 km (37–56 miles) altitude,<sup id="cite_ref-Ghosh_3-0" class="reference"><a href="#cite_note-Ghosh-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> which reflects VLF radio waves. The conductive ionosphere and the conductive Earth form a horizontal "duct" a few VLF wavelengths high, which acts as a <a href="/wiki/Waveguide" title="Waveguide">waveguide</a> confining the waves so they don't escape into space. The waves travel in a zig-zag path around the Earth, reflected alternately by the Earth and the ionosphere, in <a href="/wiki/Transverse_magnetic" class="mw-redirect" title="Transverse magnetic">transverse magnetic</a> (TM) mode. </p><p>VLF waves have very low path attenuation, 2–3 dB per 1,000 km,<sup id="cite_ref-Hunsucker_2-1" class="reference"><a href="#cite_note-Hunsucker-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> with little of the "<a href="/wiki/Fading" title="Fading">fading</a>" experienced at higher frequencies.<sup id="cite_ref-Ghosh_3-1" class="reference"><a href="#cite_note-Ghosh-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> This is because VLF waves are reflected from the bottom of the ionosphere, while higher frequency shortwave signals are returned to Earth from higher layers in the ionosphere, the <a href="/wiki/F1_layer" class="mw-redirect" title="F1 layer">F1</a> and <a href="/wiki/F2_layer" class="mw-redirect" title="F2 layer">F2</a> layers, by a refraction process, and spend most of their journey in the ionosphere, so they are much more affected by ionization gradients and turbulence. Therefore, VLF transmissions are very stable and reliable, and are used for long-distance communication. Propagation distances of 5,000–20,000 km have been realized.<sup id="cite_ref-Hunsucker_2-2" class="reference"><a href="#cite_note-Hunsucker-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> However, atmospheric noise ("<a href="/wiki/Sferics" class="mw-redirect" title="Sferics">sferics</a>") is high in the band,<sup id="cite_ref-Ghosh_3-2" class="reference"><a href="#cite_note-Ghosh-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> including such phenomena as "<a href="/wiki/Whistler_(radio)" title="Whistler (radio)">whistlers</a>", caused by <a href="/wiki/Lightning" title="Lightning">lightning</a>. </p> <ul><li>VLF waves can penetrate <a href="/wiki/Seawater" title="Seawater">seawater</a> to a depth of at least 10–40 meters (30–130 feet), depending on the frequency employed and the salinity of the water, so they are used to communicate with submarines.</li> <li>VLF waves at certain frequencies have been found to cause <a href="/wiki/Electron_precipitation" title="Electron precipitation">electron precipitation</a>.</li> <li>VLF waves used to communicate with submarines have created an artificial bubble around the Earth that can protect it from <a href="/wiki/Solar_flare" title="Solar flare">solar flares</a> and <a href="/wiki/Coronal_mass_ejection" title="Coronal mass ejection">coronal mass ejections</a>; this occurred through interaction with high-energy radiation particles.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></li></ul> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading2"><h2 id="Antennas">Antennas</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=2" title="Edit section: Antennas"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1237032888/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner img{background-color:white}}</style><div class="thumb tmulti tnone center"><div class="thumbinner multiimageinner" style="width:1094px;max-width:1094px"><div class="trow"><div class="tsingle" style="width:372px;max-width:372px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Cutler_VLF_antenna_array.png" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Cutler_VLF_antenna_array.png/370px-Cutler_VLF_antenna_array.png" decoding="async" width="370" height="166" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Cutler_VLF_antenna_array.png/555px-Cutler_VLF_antenna_array.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/70/Cutler_VLF_antenna_array.png/740px-Cutler_VLF_antenna_array.png 2x" data-file-width="1449" data-file-height="652" /></a></span></div><div class="thumbcaption">"Trideco" antenna tower array at the US Navy's <a href="/wiki/VLF_Transmitter_Cutler" title="VLF Transmitter Cutler">Naval Radio Station Cutler</a> in Cutler, Maine, USA. The central mast is the radiating element, while the star-shaped horizontal wire array is the capacitive top load. About 2 km (1.2 mi) in diameter, it communicates with submerged submarines at 24 kHz (12,500 meter wavelength) at a power of 1.8 megawatts, one of the most powerful radio stations in the world.</div></div><div class="tsingle" style="width:225px;max-width:225px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/11/VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg/223px-VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg" decoding="async" width="223" height="167" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/11/VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg/335px-VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/11/VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg/446px-VLF_umbrella_antenna_-_Anthorn_Radio_Station_UK_-_central_mast.jpg 2x" data-file-width="4592" data-file-height="3448" /></a></span></div><div class="thumbcaption">Central mast of a similar "trideco" antenna of the NATO VLF transmitter at <a href="/wiki/Anthorn_radio_station" class="mw-redirect" title="Anthorn radio station">Anthorn radio station</a>, UK, showing 6 insulator strings attaching the toploads to the 6 vertical radiator wires</div></div><div class="tsingle" style="width:267px;max-width:267px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Jim_Creek_VLF_antenna.png" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Jim_Creek_VLF_antenna.png/265px-Jim_Creek_VLF_antenna.png" decoding="async" width="265" height="167" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Jim_Creek_VLF_antenna.png/398px-Jim_Creek_VLF_antenna.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Jim_Creek_VLF_antenna.png/530px-Jim_Creek_VLF_antenna.png 2x" data-file-width="1818" data-file-height="1146" /></a></span></div><div class="thumbcaption">Another type of large VLF antenna: the "valley-span" antenna, consisting of one or more long horizontal topload cables spanning a valley, fed in the center by vertical radiator cables. This example is at the US Navy <a href="/wiki/Jim_Creek_Naval_Radio_Station" title="Jim Creek Naval Radio Station">Jim Creek station</a> near <a href="/wiki/Seattle" title="Seattle">Seattle</a>, which transmits on 24.8 kHz at a power of 1.2 MW.</div></div><div class="tsingle" style="width:222px;max-width:222px"><div class="thumbimage"><span typeof="mw:File"><a href="/wiki/File:Tsushima_Omega_Tower_1977_2.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Tsushima_Omega_Tower_1977_2.jpg/220px-Tsushima_Omega_Tower_1977_2.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/99/Tsushima_Omega_Tower_1977_2.jpg/330px-Tsushima_Omega_Tower_1977_2.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/99/Tsushima_Omega_Tower_1977_2.jpg/440px-Tsushima_Omega_Tower_1977_2.jpg 2x" data-file-width="1107" data-file-height="831" /></a></span></div><div class="thumbcaption"><a href="/wiki/Umbrella_antenna" title="Umbrella antenna">Umbrella antenna</a> of the <a href="/wiki/Omega_(navigation_system)" title="Omega (navigation system)">Omega navigation system</a> beacon on <a href="/wiki/Tsushima_Island" title="Tsushima Island">Tsushima Island</a>, Japan, which transmitted at 10-14 kHz; 389 meters high, <a href="https://ja.wikipedia.org/wiki/%E5%AF%BE%E9%A6%AC%E3%82%AA%E3%83%A1%E3%82%AC%E5%B1%80" class="extiw" title="ja:対馬オメガ局">it was dismantled in 1998</a>.</div></div></div></div></div> <p>A major practical drawback to the VLF band is that because of the length of the waves, full size resonant antennas (<a href="/wiki/Half_wave_dipole" class="mw-redirect" title="Half wave dipole">half wave dipole</a> or <a href="/wiki/Monopole_antenna" title="Monopole antenna">quarter wave monopole</a> antennas) cannot be built because of their physical height.<sup id="cite_ref-Watt_5-0" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages: 14">: 14 </span></sup> Vertical antennas must be used because VLF waves propagate in vertical polarization, but a quarter-wave vertical antenna at 30 kHz (10 km wavelength) would be 2.5 kilometres (8,200 feet) high. So practical transmitting antennas are <a href="/wiki/Electrical_length" title="Electrical length">electrically short</a>, a small fraction of the length at which they would be self-resonant.<sup id="cite_ref-Seybold_6-0" class="reference"><a href="#cite_note-Seybold-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Johnson-1993_7-0" class="reference"><a href="#cite_note-Johnson-1993-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages:  24.5–24.6">:  24.5–24.6 </span></sup> Due to their low <a href="/wiki/Radiation_resistance" title="Radiation resistance">radiation resistance</a> (often less than one ohm) they are inefficient, radiating only 10% to 50% of the transmitter power at most,<sup id="cite_ref-Hunsucker_2-3" class="reference"><a href="#cite_note-Hunsucker-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Watt_5-1" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: 14">: 14 </span></sup> with the rest of the power dissipated in the antenna/ground system resistances. Very high power transmitters (~1 megawatt) are required for long-distance communication, so the efficiency of the antenna is an important factor. </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Flattop_antenna_1912.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Flattop_antenna_1912.png/220px-Flattop_antenna_1912.png" decoding="async" width="220" height="130" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Flattop_antenna_1912.png/330px-Flattop_antenna_1912.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Flattop_antenna_1912.png/440px-Flattop_antenna_1912.png 2x" data-file-width="888" data-file-height="524" /></a><figcaption>A "triatic" or "<a href="/wiki/Inverted-L_antenna" class="mw-redirect" title="Inverted-L antenna">flattop</a>" antenna, another common VLF transmitting antenna. It consists of vertical radiator wires each connected at top to parallel horizontal capacitive topload wires stretching up to a kilometer, supported on tall towers. The transverse support cables suspending the horizontal wires are called "triatics".</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="VLF_transmitting_antennas">VLF transmitting antennas</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=3" title="Edit section: VLF transmitting antennas"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>High power VLF transmitting stations use capacitively-toploaded <a href="/wiki/Monopole_antenna" title="Monopole antenna">monopole antennas</a>. These are very large wire antennas, up to several kilometers long.<sup id="cite_ref-NAVELEX-0101-113_8-0" class="reference"><a href="#cite_note-NAVELEX-0101-113-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages:  3.9–3.21">:  3.9–3.21 </span></sup><sup id="cite_ref-Johnson-1993_7-1" class="reference"><a href="#cite_note-Johnson-1993-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages:  24.8–24.12">:  24.8–24.12 </span></sup> They consist of a series of steel <a href="/wiki/Radio_mast" class="mw-redirect" title="Radio mast">radio masts</a>, linked at the top with a network of cables, often shaped like an umbrella or clotheslines.<sup id="cite_ref-Watt_5-2" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p.14">: p.14 </span></sup> Either the towers themselves or vertical wires serve as <a href="/wiki/Monopole_antenna" title="Monopole antenna">monopole</a> radiators, and the horizontal cables form a <i>capacitive top-load</i> to increase the current in the vertical wires, increasing the radiated power and efficiency of the antenna. High-power stations use variations on the <a href="/wiki/Umbrella_antenna" title="Umbrella antenna">umbrella antenna</a> such as the "delta" and "<a href="/wiki/Umbrella_antenna#Trideco_antenna" title="Umbrella antenna">trideco</a>" antennas, or multiwire <a href="/wiki/T-aerial" class="mw-redirect" title="T-aerial">flattop</a> (triatic) antennas.<sup id="cite_ref-Watt_5-3" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages: p.129-162">: p.129-162 </span></sup> For low-power transmitters, inverted-L and <a href="/wiki/T-aerial" class="mw-redirect" title="T-aerial">T antennas</a> are used. </p><p>Due to the low radiation resistance, to minimize power dissipated in the ground these antennas require extremely low resistance <a href="/wiki/Ground_(electricity)" title="Ground (electricity)">ground</a> (Earthing) systems, consisting of radial networks of buried copper wires under the antenna. To minimize <a href="/wiki/Dielectric_loss" title="Dielectric loss">dielectric losses</a> in the soil, the ground conductors are buried shallowly, only a few inches in the ground, and the ground surface near the antenna is sometimes protected by copper ground screens. <a href="/wiki/Counterpoise_(ground_system)" title="Counterpoise (ground system)">Counterpoise</a> systems have also been used, consisting of radial networks of copper cables supported several feet above the ground under the antenna. </p><p>A large <a href="/wiki/Loading_coil" title="Loading coil">loading coil</a> is required at the antenna feed point to cancel the <a href="/wiki/Capacitive_reactance" class="mw-redirect" title="Capacitive reactance">capacitive reactance</a> of the antenna to make it <a href="/wiki/Resonant" class="mw-redirect" title="Resonant">resonant</a>. At VLF the design of this coil is challenging; it must have low resistance at the operating RF frequency, <a href="/wiki/Q_factor" title="Q factor">high <span class="texhtml mvar" style="font-style:italic;">Q</span></a>, must handle very high currents, and must withstand the extremely high voltage on the antenna. These are usually huge air core coils 2-4 meters high wound on a nonconductive frame, with RF resistance reduced by using thick <a href="/wiki/Litz_wire" title="Litz wire">litz wire</a> several centimeters in diameter, consisting of thousands of insulated strands of fine wire braided together.<sup id="cite_ref-Watt_5-4" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p.95">: p.95 </span></sup> </p><p>The high capacitance and inductance and low resistance of the antenna-loading coil combination makes it act electrically like a <a href="/wiki/Q_factor" title="Q factor">high <span class="texhtml mvar" style="font-style:italic;">Q</span></a> <a href="/wiki/Tuned_circuit" class="mw-redirect" title="Tuned circuit">tuned circuit</a>. VLF antennas have very narrow <a href="/wiki/Bandwidth_(signal_processing)" title="Bandwidth (signal processing)">bandwidth</a> and to change the transmitting frequency requires a variable inductor (<a href="/wiki/Transformer_types#Variometer_and_variocoupler" title="Transformer types">variometer</a>) to tune the antenna. The large VLF antennas used for high-power transmitters usually have bandwidths of only 50–100 hertz. The high <span class="texhtml mvar" style="font-style:italic;">Q</span> results in very high voltages (up to 250 kV)<sup id="cite_ref-Watt_5-5" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p.58">: p.58 </span></sup> on the antenna and very good insulation is required.<sup id="cite_ref-Watt_5-6" class="reference"><a href="#cite_note-Watt-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p.14,19">: p.14,19 </span></sup> Large VLF antennas usually operate in 'voltage limited' mode: the maximum power of the transmitter is limited by the voltage the antenna can accept without <a href="/wiki/Electrical_breakdown" title="Electrical breakdown">air breakdown</a>, <a href="/wiki/Corona_discharge" title="Corona discharge">corona</a>, and arcing from the antenna. </p> <div class="mw-heading mw-heading3"><h3 id="Dynamic_antenna_tuning">Dynamic antenna tuning</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=4" title="Edit section: Dynamic antenna tuning"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The bandwidth of large capacitively loaded VLF antennas is so narrow (50–100 Hz) that even the small frequency shifts of FSK and MSK modulation may exceed it, throwing the antenna out of <a href="/wiki/Resonance" title="Resonance">resonance</a>, causing the antenna to reflect some power back down the feedline. The traditional solution is to use a "bandwidth resistor" in the antenna which reduces the <span class="texhtml mvar" style="font-style:italic;">Q</span>, increasing the bandwidth; however this also reduces the power output. A recent alternative used in some military VLF transmitters is a circuit which dynamically shifts the antenna's <a href="/wiki/Resonant_frequency" class="mw-redirect" title="Resonant frequency">resonant frequency</a> between the two output frequencies with the modulation.<sup id="cite_ref-Johnson-1993_7-2" class="reference"><a href="#cite_note-Johnson-1993-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: 24.7">:  24.7 </span></sup><sup id="cite_ref-NAVELEX-0101-113_8-1" class="reference"><a href="#cite_note-NAVELEX-0101-113-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: 3.36">:  3.36 </span></sup> This is accomplished with a <a href="/wiki/Saturable_reactor" title="Saturable reactor">saturable reactor</a> in series with the antenna <a href="/wiki/Loading_coil" title="Loading coil">loading coil</a>. This is a <a href="/wiki/Magnetic_core" title="Magnetic core">ferromagnetic core</a> <a href="/wiki/Inductor" title="Inductor">inductor</a> with a second control winding through which a DC current flows, which controls the inductance by magnetizing the core, changing its <a href="/wiki/Magnetic_permeability" class="mw-redirect" title="Magnetic permeability">permeability</a>. The keying datastream is applied to the control winding. So when the frequency of the transmitter is shifted between the '1' and '0' frequencies, the saturable reactor changes the inductance in the antenna resonant circuit to shift the antenna resonant frequency to follow the transmitter's frequency. </p> <div class="mw-heading mw-heading3"><h3 id="VLF_receiving_antennas">VLF receiving antennas</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=5" title="Edit section: VLF receiving antennas"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The requirements for receiving antennas are less stringent, because of the high level of natural <a href="/wiki/Atmospheric_noise" title="Atmospheric noise">atmospheric noise</a> in the band. At VLF frequencies atmospheric <a href="/wiki/Radio_noise" title="Radio noise">radio noise</a> is far above the <a href="/wiki/Noise_figure" title="Noise figure">receiver noise</a> introduced by the receiver circuit and determines the receiver <a href="/wiki/Signal-to-noise_ratio" title="Signal-to-noise ratio">signal-to-noise ratio</a>. So small inefficient receiving antennas can be used, and the low voltage signal from the antenna can simply be amplified by the receiver without introducing significant noise. Ferrite <a href="/wiki/Loop_antenna" title="Loop antenna">loop antennas</a> are usually used for reception. </p> <div class="mw-heading mw-heading2"><h2 id="Modulation">Modulation</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=6" title="Edit section: Modulation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Because of the small <a href="/wiki/Bandwidth_(signal_processing)" title="Bandwidth (signal processing)">bandwidth</a> of the band, and the extremely narrow bandwidth of the antennas used, it is impractical to transmit <a href="/wiki/Audio_signal" title="Audio signal">audio signals</a> (<a href="/wiki/Amplitude_modulation" title="Amplitude modulation">AM</a> or <a href="/wiki/Frequency_modulation" title="Frequency modulation">FM</a> <a href="/wiki/Radiotelephony" class="mw-redirect" title="Radiotelephony">radiotelephony</a>).<sup id="cite_ref-Holtet_9-0" class="reference"><a href="#cite_note-Holtet-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> A typical AM radio signal with a bandwidth of 10 kHz would occupy one third of the VLF band. More significantly, it would be difficult to transmit any distance because it would require an antenna with 100 times the bandwidth of current VLF antennas, which due to the <a href="/wiki/Chu-Harrington_limit" class="mw-redirect" title="Chu-Harrington limit">Chu-Harrington limit</a> would be enormous in size. Therefore, only text data can be transmitted, at low <a href="/wiki/Bit_rate" title="Bit rate">bit rates</a>. In military networks <a href="/wiki/Frequency-shift_keying" title="Frequency-shift keying">frequency-shift keying</a> (FSK) <a href="/wiki/Modulation" title="Modulation">modulation</a> is used to transmit <a href="/wiki/Radioteletype" title="Radioteletype">radioteletype</a> data using 5 bit <a href="/wiki/ITA2" class="mw-redirect" title="ITA2">ITA2</a> or 8 bit <a href="/wiki/ASCII" title="ASCII">ASCII</a> character codes. A small frequency shift of 30–50 hertz is used due to the small bandwidth of the antenna. </p><p>In high power VLF transmitters, to increase the allowable data rate, a special form of FSK called <a href="/wiki/Minimum-shift_keying" title="Minimum-shift keying">minimum-shift keying</a> (MSK) is used. This is required due to the high <span class="texhtml mvar" style="font-style:italic;"><a href="/wiki/Q_factor" title="Q factor">Q</a></span> of the antenna.<sup id="cite_ref-NAVELEX-0101-113_8-2" class="reference"><a href="#cite_note-NAVELEX-0101-113-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages:  3.2–3.4, §3.1.1">:  3.2–3.4, §3.1.1 </span></sup> The huge capacitively-loaded antenna and <a href="/wiki/Loading_coil" title="Loading coil">loading coil</a> form a high <span class="texhtml mvar" style="font-style:italic;">Q</span> <a href="/wiki/Tuned_circuit" class="mw-redirect" title="Tuned circuit">tuned circuit</a>, which stores oscillating electrical energy. The <span class="texhtml mvar" style="font-style:italic;">Q</span> of large VLF antennas is typically over 200; this means the antenna stores far more energy (200 times as much) than is supplied or radiated in any single cycle of the transmitter current. The energy is stored alternately as <a href="/wiki/Electrostatic_energy" class="mw-redirect" title="Electrostatic energy">electrostatic energy</a> in the topload and ground system, and magnetic energy in the vertical wires and loading coil. VLF antennas typically operate "voltage-limited", with the voltage on the antenna close to the limit that the insulation will stand, so they will not tolerate any abrupt change in the voltage or current from the transmitter without arcing or other insulation problems. As described below, MSK is able to modulate the transmitted wave at higher data rates without causing voltage spikes on the antenna. </p><p>The three types of <a href="/wiki/Modulation" title="Modulation">modulation</a> that have been used in VLF transmitters are: </p> <dl><dt><a href="/wiki/Continuous_Wave" class="mw-redirect" title="Continuous Wave">Continuous Wave</a> (CW), Interrupted Continuous Wave (ICW), or On-Off Keying</dt> <dd><a href="/wiki/Morse_code" title="Morse code">Morse code</a> <a href="/wiki/Radiotelegraphy" class="mw-redirect" title="Radiotelegraphy">radiotelegraphy</a> transmission with unmodulated carrier. The carrier is turned on and off, with carrier on representing the Morse code "dots" and "dashes" and carrier off representing spaces. The simplest and earliest form of radio data transmission, this was used from the beginning of the 20th century to the 1960s in commercial and military VLF stations. Because of the high <a href="/wiki/Q_factor" title="Q factor">antenna <span class="texhtml mvar" style="font-style:italic;">Q</span></a> the carrier cannot be switched abruptly on and off but requires a long time constant, many cycles, to build up the oscillating energy in the antenna when the carrier turns on, and many cycles to dissipate the stored energy when the carrier turns off. This limits the data rate that can be transmitted to 15–20 words/minute. CW is now only used in small hand-keyed transmitters, and for testing large transmitters.</dd> <dt><a href="/wiki/Frequency-shift_keying" title="Frequency-shift keying">Frequency-shift keying</a> (FSK)</dt> <dd>FSK is the second oldest and second simplest form of digital radio data modulation, after CW. For FSK, the carrier shifted between two frequencies, one representing the binary digit '1' and the other representing binary '0'. For example, a frequency of 9070 Hz might be used to indicate a '1' and the frequency 9020 Hz, 50 Hz lower, to indicate a '0'. The two frequencies are generated by a continuously-running <a href="/wiki/Frequency_synthesizer" title="Frequency synthesizer">frequency synthesizer</a>. The transmitter is periodically switched between these frequencies to represent 8 bit <a href="/wiki/ASCII" title="ASCII">ASCII</a> codes for the characters of the message. A problem at VLF is that when the frequency is switched the two <a href="/wiki/Sine_wave" title="Sine wave">sine waves</a> usually have different <a href="/wiki/Phase_(waves)" title="Phase (waves)">phases</a>, which creates a sudden phase-shift transient which can cause arcing on the antenna. To avoid arcing, FSK can only be used at slow rates of 50–75 bit/s.</dd> <dt><a href="/wiki/Minimum-shift_keying" title="Minimum-shift keying">Minimum-shift keying</a> (MSK)</dt> <dd>A <a href="/wiki/Continuous_phase_modulation" title="Continuous phase modulation">continuous phase</a> version of FSK designed specifically for small bandwidths, this was adopted by naval VLF stations in the 1970s to increase the data rate and is now the standard mode used in military VLF transmitters. If the two frequencies representing '1' and '0' are 50 Hz apart, the standard frequency shift used in military VLF stations, their phases coincide every 20 ms. In MSK the frequency of the transmitter is switched only when the two sine waves have the same phase, at the point both sine waves cross zero in the same direction. This creates a smooth continuous transition between the waves, avoiding transients which can cause stress and arcing on the antenna. MSK can be used at data rates up to 300 bit/s, or about 35 <a href="/wiki/ASCII" title="ASCII">ASCII</a> characters (8 bits each) per second, approximately 450 words per minute.</dd></dl> <div class="mw-heading mw-heading2"><h2 id="Applications">Applications</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=7" title="Edit section: Applications"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Grimetonmasterna.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Grimetonmasterna.jpg/220px-Grimetonmasterna.jpg" decoding="async" width="220" height="534" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/8/8e/Grimetonmasterna.jpg 1.5x" data-file-width="230" data-file-height="558" /></a><figcaption><a href="/wiki/T_antenna" class="mw-redirect" title="T antenna">Flattop antenna</a> towers of the <a href="/wiki/Grimeton_Radio_Station" title="Grimeton Radio Station">Grimeton VLF transmitter</a>, Varberg, Sweden</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Early_wireless_telegraphy">Early wireless telegraphy</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=8" title="Edit section: Early wireless telegraphy"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Historically, this band was used for long distance transoceanic radio communication during the <a href="/wiki/Wireless_telegraphy" title="Wireless telegraphy">wireless telegraphy</a> era between about 1905 and 1925. Nations built networks of high-power LF and VLF <a href="/wiki/Radiotelegraphy" class="mw-redirect" title="Radiotelegraphy">radiotelegraphy</a> stations that transmitted text information by <a href="/wiki/Morse_code" title="Morse code">Morse code</a>, to communicate with other countries, their colonies, and naval fleets. Early attempts were made to use radiotelephone using <a href="/wiki/Amplitude_modulation" title="Amplitude modulation">amplitude modulation</a> and <a href="/wiki/Single-sideband_modulation" title="Single-sideband modulation">single-sideband modulation</a> within the band starting from 20 kHz, but the result was unsatisfactory because the available bandwidth was insufficient to contain the <a href="/wiki/Sideband" title="Sideband">sidebands</a>. </p><p>In the 1920s the discovery of the <a href="/wiki/Skywave" title="Skywave">skywave</a> (skip) radio propagation method allowed lower power transmitters operating at <a href="/wiki/High_frequency" title="High frequency">high frequency</a> to communicate at similar distances by reflecting their radio waves off a layer of <a href="/wiki/Ionization" title="Ionization">ionized</a> atoms in the <a href="/wiki/Ionosphere" title="Ionosphere">ionosphere</a>, and long-distance radio communication stations switched to the <a href="/wiki/Shortwave" class="mw-redirect" title="Shortwave">shortwave</a> frequencies. The <a href="/wiki/Grimeton_VLF_transmitter" class="mw-redirect" title="Grimeton VLF transmitter">Grimeton VLF transmitter</a> at Grimeton near Varberg in <a href="/wiki/Sweden" title="Sweden">Sweden</a>, one of the few remaining transmitters from that era that has been preserved as a historical monument, can be visited by the public at certain times, such as on <a href="/wiki/Alexanderson_Day" title="Alexanderson Day">Alexanderson Day</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Navigation_beacons_and_time_signals">Navigation beacons and time signals</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=9" title="Edit section: Navigation beacons and time signals"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Due to its long propagation distances and stable phase characteristics, during the 20th century the VLF band was used for long range <a href="/wiki/Hyperbolic_navigation" title="Hyperbolic navigation">hyperbolic</a> <a href="/wiki/Radio_navigation" title="Radio navigation">radio navigation</a> systems which allowed ships and aircraft to determine their geographical position by comparing the phase of radio waves received from fixed VLF <a href="/wiki/Navigation_beacon" class="mw-redirect" title="Navigation beacon">navigation beacon</a> transmitters. </p><p>The worldwide <a href="/wiki/Omega_(navigation_system)" title="Omega (navigation system)">Omega</a> system used frequencies from 10 to 14 kHz, as did Russia's <a href="/wiki/Alpha_(navigation)" title="Alpha (navigation)">Alpha</a>. </p><p>VLF was also used for <a href="/wiki/Standard_time_and_frequency_signal" class="mw-redirect" title="Standard time and frequency signal">standard time and frequency</a> broadcasts. In the US, the <a href="/wiki/Time_signal" title="Time signal">time signal</a> station <a href="/wiki/WWVL" class="mw-redirect" title="WWVL">WWVL</a> began transmitting a 500 W signal on 20 kHz in August 1963. It used frequency-shift keying (<a href="/wiki/Frequency-shift_keying" title="Frequency-shift keying">FSK</a>) to send data, shifting between 20 kHz and 26 kHz. The WWVL service was discontinued in July 1972. </p> <div class="mw-heading mw-heading3"><h3 id="Geophysical_and_atmospheric_measurement">Geophysical and atmospheric measurement</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=10" title="Edit section: Geophysical and atmospheric measurement"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Naturally occurring signals in the VLF band are used by <a href="/wiki/Geophysicist" class="mw-redirect" title="Geophysicist">geophysicists</a> for long range lightning location and for research into atmospheric phenomena such as the aurora. Measurements of <a href="/wiki/Whistler_(radio)" title="Whistler (radio)">whistlers</a> are employed to infer the physical properties of the <a href="/wiki/Magnetosphere" title="Magnetosphere">magnetosphere</a>.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Geophysicists" class="mw-redirect" title="Geophysicists">Geophysicists</a> use VLF-<a href="/wiki/Electromagnetic" class="mw-redirect" title="Electromagnetic">electromagnetic</a> receivers to measure conductivity in the near surface of the Earth.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p><p>VLF signals can be measured as a <a href="/wiki/Geophysics" title="Geophysics">geophysical</a> <a href="/wiki/Electromagnetic" class="mw-redirect" title="Electromagnetic">electromagnetic</a> survey that relies on transmitted currents inducing secondary responses in conductive geologic units. A VLF anomaly represents a change in the attitude of the electromagnetic vector overlying conductive materials in the subsurface. </p> <div class="mw-heading mw-heading3"><h3 id="Mine_communication_systems">Mine communication systems</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=11" title="Edit section: Mine communication systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>VLF can also penetrate soil and rock for some distance, so these frequencies are also used for <a href="/wiki/Through-the-earth_mine_communications" title="Through-the-earth mine communications">through-the-earth mine communications</a> systems. </p> <div class="mw-heading mw-heading3"><h3 id="Military_communications">Military communications</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=12" title="Edit section: Military communications"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Powerful VLF transmitters are used by the military to communicate with their forces worldwide. The advantage of VLF frequencies is their long range, high reliability, and the prediction that in a <a href="/wiki/Nuclear_war" class="mw-redirect" title="Nuclear war">nuclear war</a> VLF communications will be less disrupted by nuclear explosions than higher frequencies. Since it can penetrate seawater VLF is used by the military to <a href="/wiki/Communication_with_submarines" title="Communication with submarines">communicate with submarines</a> near the surface, while <a href="/wiki/Extremely_low_frequency" title="Extremely low frequency">ELF</a> frequencies are used for deeply submerged subs. </p><p>Examples of naval VLF transmitters are </p> <ul><li>Britain's <a href="/wiki/Skelton_Transmitting_Station" title="Skelton Transmitting Station">Skelton Transmitting Station</a> in Skelton, Cumbria</li> <li>Germany's <a href="/wiki/VLF_transmitter_DHO38" title="VLF transmitter DHO38">DHO38</a> in <a href="/wiki/Rhauderfehn" title="Rhauderfehn">Rhauderfehn</a>, which transmits on 23.4 kHz with a power of 800 kW</li> <li>U.S. <a href="/wiki/Jim_Creek_Naval_Radio_Station" title="Jim Creek Naval Radio Station">Jim Creek Naval Radio Station</a> in <a href="/wiki/Oso,_Washington" title="Oso, Washington">Oso, Washington</a> state, which transmits on 24.8 kHz with a power of 1.2 MW</li> <li>U.S. <a href="/wiki/VLF_Transmitter_Cutler" title="VLF Transmitter Cutler">Cutler Naval Radio Station</a> at <a href="/wiki/Cutler,_Maine" title="Cutler, Maine">Cutler, Maine</a> which transmits on 24 kHz with 1.8 MW.</li></ul> <p>Since 2004 the <a href="/wiki/US_Navy" class="mw-redirect" title="US Navy">US Navy</a> has stopped using ELF transmissions, with the statement that improvements in VLF communication has made them unnecessary, so it may have developed technology to allow submarines to receive VLF transmissions while at operating depth. </p><p>High power land-based and aircraft transmitters in countries that operate submarines send signals that can be received thousands of miles away. Transmitter sites typically cover great areas (many <a href="/wiki/Acres" class="mw-redirect" title="Acres">acres</a> or square kilometers), with transmitted power anywhere from 20 kW to 2,000 kW. Submarines receive signals from land based and aircraft transmitters using some form of towed antenna that floats just under the surface of the water – for example a <a href="/w/index.php?title=Buoyant_Cable_Array_Antenna&action=edit&redlink=1" class="new" title="Buoyant Cable Array Antenna (page does not exist)">Buoyant Cable Array Antenna</a> (BCAA). </p><p>Modern receivers use sophisticated <a href="/wiki/Digital_signal_processing" title="Digital signal processing">digital signal processing</a> techniques to remove the effects of atmospheric noise (largely caused by lightning strikes around the world) and adjacent channel signals, extending the useful reception range. Strategic nuclear bombers of the United States Air Force receive VLF signals as part of hardened nuclear resilient operations. </p><p>Two alternative character sets may be used: 5 bit <a href="/wiki/ITA2" class="mw-redirect" title="ITA2">ITA2</a> or 8 bit <a href="/wiki/ASCII" title="ASCII">ASCII</a>. Because these are military transmissions they are almost always <a href="/wiki/Encrypted" class="mw-redirect" title="Encrypted">encrypted</a> for security reasons. Although it is relatively easy to receive the transmissions and convert them into a string of characters, enemies cannot decode the encrypted messages; military communications usually use unbreakable <a href="/wiki/One-time_pad" title="One-time pad">one-time pad</a> <a href="/wiki/Cipher" title="Cipher">ciphers</a> since the amount of text is so small. </p> <div class="mw-heading mw-heading2"><h2 id="Amateur_use">Amateur use</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=13" title="Edit section: Amateur use"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The frequency range below 8.3 kHz is not allocated by the <a href="/wiki/International_Telecommunication_Union" title="International Telecommunication Union">International Telecommunication Union</a> and in some nations may be used license-free. Radio amateurs in some countries have been granted permission (or have assumed permission) to operate at frequencies below 8.3 kHz.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>Operations tend to congregate around the frequencies 8.27 kHz, 6.47 kHz, 5.17 kHz, and 2.97 kHz.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> Transmissions typically last from one hour up to several days and both receiver and transmitter must have their frequency locked to a stable reference such as a <a href="/wiki/GPS_disciplined_oscillator" title="GPS disciplined oscillator">GPS disciplined oscillator</a> or a <a href="/wiki/Rubidium_standard" title="Rubidium standard">rubidium standard</a> in order to support such long duration coherent detection and decoding. </p> <div class="mw-heading mw-heading3"><h3 id="Amateur_equipment">Amateur equipment</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=14" title="Edit section: Amateur equipment"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Radiated power from amateur stations is very small, ranging from 1 μW to 100 μW for fixed base station antennas, and up to 10 mW from kite or balloon antennas. Despite the low power, stable propagation with low attenuation in the <a href="/wiki/Earth-ionosphere_waveguide" class="mw-redirect" title="Earth-ionosphere waveguide">earth-ionosphere cavity</a> enable very narrow bandwidths to be used to reach distances up to several thousand kilometers. The modes used are <a href="/wiki/QRP_operation#QRSS" title="QRP operation">QRSS</a>, <a href="/wiki/Multiple_frequency-shift_keying" title="Multiple frequency-shift keying">MFSK</a>, and coherent <a href="/wiki/Phase-shift_keying" title="Phase-shift keying">BPSK</a>. </p><p>The transmitter generally consists of an audio amplifier of a few hundred watts, an impedance matching transformer, a <a href="/wiki/Loading_coil" title="Loading coil">loading coil</a> and a large wire antenna. Receivers employ an electric field probe or magnetic loop antenna, a sensitive audio preamplifier, isolating transformers, and a PC <a href="/wiki/Sound_card" title="Sound card">sound card</a> to digitise the signal. Extensive <a href="/wiki/Digital_signal_processing" title="Digital signal processing">digital signal processing</a> is required to retrieve the weak signals from beneath <a href="/wiki/Electromagnetic_interference" title="Electromagnetic interference">interference</a> from <a href="/wiki/Harmonics_(electrical_power)" title="Harmonics (electrical power)">power line harmonics</a> and <a href="/wiki/Radio_atmospheric" class="mw-redirect" title="Radio atmospheric">VLF radio atmospherics</a>. Useful received signal strengths are as low as <span class="nowrap"><span data-sort-value="6992300000000000000♠"></span>3<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−8</sup></span> volts/meter (electric field) and <span class="nowrap"><span data-sort-value="6984100000000000000♠"></span>1<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−16</sup></span> tesla (magnetic field), with <a href="/wiki/Signaling_rate" class="mw-redirect" title="Signaling rate">signaling rates</a> typically between 1 and 100 bits per hour. </p> <div class="mw-heading mw-heading3"><h3 id="PC_based_reception">PC based reception</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=15" title="Edit section: PC based reception"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:VLF_18.1_kHz_spectrogram.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b3/VLF_18.1_kHz_spectrogram.svg/220px-VLF_18.1_kHz_spectrogram.svg.png" decoding="async" width="220" height="89" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b3/VLF_18.1_kHz_spectrogram.svg/330px-VLF_18.1_kHz_spectrogram.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b3/VLF_18.1_kHz_spectrogram.svg/440px-VLF_18.1_kHz_spectrogram.svg.png 2x" data-file-width="721" data-file-height="293" /></a><figcaption>Timing diagram of a frequency-shift keyed 18.1 kHz VLF signal, picked up using a small <a href="/wiki/Loop_antenna" title="Loop antenna">loop antenna</a> and a sound card. The Morse code says "..33376.."; the vertical stripes are distant lightning strikes.</figcaption></figure> <p>VLF signals are often monitored by <a href="/wiki/Radio_amateur" class="mw-redirect" title="Radio amateur">radio amateurs</a> using simple homemade VLF <a href="/wiki/Radio_receiver" title="Radio receiver">radio receivers</a> based on personal computers (PCs).<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> An aerial in the form of a coil of insulated wire is connected to the input of the soundcard of the PC (via a jack plug) and placed a few meters away from it. <a href="/wiki/Fast_Fourier_transform" title="Fast Fourier transform">Fast Fourier transform</a> (FFT) software in combination with a sound card allows reception of all frequencies below the <a href="/wiki/Nyquist_frequency" title="Nyquist frequency">Nyquist frequency</a> simultaneously in the form of <a href="/wiki/Spectrogram" title="Spectrogram">spectrogrammes</a>. </p><p>Because CRT monitors are strong sources of noise in the VLF range, it is recommended to record the spectrograms with any PC CRT monitors turned off. These spectrograms show many signals, which may include VLF transmitters and the horizontal electron beam deflection of TV sets. The strength of the signal received can vary with a <a href="/wiki/Sudden_Ionospheric_Disturbance" class="mw-redirect" title="Sudden Ionospheric Disturbance">sudden ionospheric disturbance</a>. These cause the ionization level to increase in the ionosphere producing a rapid change to the amplitude and phase of the received VLF signal. </p> <div class="mw-heading mw-heading2"><h2 id="List_of_VLF_transmissions">List of VLF transmissions</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=16" title="Edit section: List of VLF transmissions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>For a more detailed list, see <a href="/wiki/List_of_VLF-transmitters" title="List of VLF-transmitters">List of VLF-transmitters</a> </p> <table class="wikitable sortable"> <tbody><tr> <th>Callsign </th> <th>Frequency </th> <th>Location of transmitter </th> <th>Remarks </th></tr> <tr align="center" valign="top"> <td>—</td> <td>11.905 kHz</td> <td>various locations (Russia)</td> <td><a href="/wiki/Alpha_(radio_navigation)" class="mw-redirect" title="Alpha (radio navigation)">Alpha-Navigation</a> </td></tr> <tr align="center" valign="top"> <td>—</td> <td>12.649 kHz</td> <td>various locations (Russia)</td> <td><a href="/wiki/Alpha_(radio_navigation)" class="mw-redirect" title="Alpha (radio navigation)">Alpha-Navigation</a> </td></tr> <tr align="center" valign="top"> <td>—</td> <td>14.881 kHz</td> <td>various locations (Russia)</td> <td><a href="/wiki/Alpha_(radio_navigation)" class="mw-redirect" title="Alpha (radio navigation)">Alpha-Navigation</a> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/HWU_transmitter" title="HWU transmitter">HWU</a></td> <td>15.1 kHz</td> <td>Rosnay (France)</td> <td>400 kW<sup id="cite_ref-Fidani-2011_16-0" class="reference"><a href="#cite_note-Fidani-2011-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </td></tr> <tr align="center" valign="top"> <td>—</td> <td>15.625 kHz</td> <td>—</td> <td>Frequency for horizontal deflection of electron beam in <a href="/wiki/CRT_television" class="mw-redirect" title="CRT television">CRT televisions</a> (<a href="/wiki/576i" title="576i">576i</a>) </td></tr> <tr align="center" valign="top"> <td>—</td> <td>15.734 kHz</td> <td>—</td> <td>Frequency for horizontal deflection of electron beam in <a href="/wiki/CRT_television" class="mw-redirect" title="CRT television">CRT televisions</a> (<a href="/wiki/480i" title="480i">480i</a>) </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Noviken_VLF_Transmitter" title="Noviken VLF Transmitter">JXN</a></td> <td>16.4 kHz</td> <td><a href="/wiki/Gildesk%C3%A5l_Municipality" title="Gildeskål Municipality">Gildeskål Municipality</a> (Norway)</td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/VLF_transmitter_Grimeton" class="mw-redirect" title="VLF transmitter Grimeton">SAQ</a></td> <td>17.2 kHz</td> <td><a href="/wiki/VLF_transmitter_Grimeton" class="mw-redirect" title="VLF transmitter Grimeton">Grimeton</a> (Sweden)</td> <td>Only active at special occasions <span class="nowrap">(<a href="/wiki/Alexanderson_Day" title="Alexanderson Day">Alexanderson Day</a>)</span> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/VLF_Transmitter_Cutler" title="VLF Transmitter Cutler">NAA</a></td> <td>17.8 kHz</td> <td>VLF station (NAA) at <a href="/wiki/Cutler,_Maine" title="Cutler, Maine">Cutler</a>, Maine (US)<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup></td> <td> </td></tr> <tr align="center" valign="top"> <td>RDL UPD UFQE UPP UPD8</td> <td>18.1 kHz</td> <td>various locations, including <a href="/wiki/Matochkin_Shar" class="mw-redirect" title="Matochkin Shar">Matochkin Shar</a> (Russia)<sup id="cite_ref-Fidani-2011_16-1" class="reference"><a href="#cite_note-Fidani-2011-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup></td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/HWU_transmitter" title="HWU transmitter">HWU</a></td> <td>18.3 kHz</td> <td><a href="/wiki/Le_Blanc" title="Le Blanc">Le Blanc</a> (France)</td> <td>Frequently inactive for long periods </td></tr> <tr align="center" valign="top"> <td>RKS</td> <td>18.9 kHz</td> <td>various locations (Russia)</td> <td>Rarely active </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Anthorn_Radio_Station" title="Anthorn Radio Station">GQD</a></td> <td>19.6 kHz</td> <td><a href="/wiki/Anthorn_radio_station" class="mw-redirect" title="Anthorn radio station">Anthorn</a> (UK)</td> <td>Many operation modes. </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Naval_Communication_Station_Harold_E._Holt" title="Naval Communication Station Harold E. Holt">NWC</a></td> <td>19.8 kHz</td> <td><a href="/wiki/Exmouth,_Western_Australia" title="Exmouth, Western Australia">Exmouth</a>, Western Australia (AUS)</td> <td>Used for submarine communication, 1 megawatt.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> </td></tr> <tr align="center" valign="top"> <td>ICV</td> <td>20.27 kHz</td> <td><a href="/wiki/Tavolara_Island" title="Tavolara Island">Tavolara</a> (Italy)</td> <td> </td></tr> <tr align="center" valign="top"> <td>RJH63 RJH66 <a href="/wiki/Vileyka_VLF_transmitter" title="Vileyka VLF transmitter">RJH69</a> RJH77 RJH99</td> <td>20.5 kHz</td> <td>various locations (Russia)</td> <td><a href="/wiki/Beta_(time_signal)" title="Beta (time signal)">Time signal transmitter Beta</a> </td></tr> <tr align="center" valign="top"> <td>ICV</td> <td>20.76 kHz</td> <td>Tavolara (Italy)</td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/HWU_transmitter" title="HWU transmitter">HWU</a></td> <td>20.9 kHz</td> <td>Saint-Assise (France)<sup id="cite_ref-Fidani-2011_16-2" class="reference"><a href="#cite_note-Fidani-2011-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup></td> <td> </td></tr> <tr align="center" valign="top"> <td>RDL</td> <td>21.1 kHz</td> <td>various locations (Russia)</td> <td>rarely active </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Lualualei_VLF_transmitter" title="Lualualei VLF transmitter">NPM</a></td> <td>21.4 kHz</td> <td>Hawaii (USA)</td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/HWU_transmitter" title="HWU transmitter">HWU</a></td> <td>21.75 kHz</td> <td>Rosnay (France)<sup id="cite_ref-Fidani-2011_16-3" class="reference"><a href="#cite_note-Fidani-2011-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup></td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Skelton_Transmitting_Station" title="Skelton Transmitting Station">GZQ</a></td> <td>22.1 kHz</td> <td><a href="/wiki/Skelton_transmitting_station" class="mw-redirect" title="Skelton transmitting station">Skelton</a> (UK)</td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Ebino_VLF_transmitter" title="Ebino VLF transmitter">JJI</a></td> <td>22.2 kHz</td> <td><a href="/wiki/Ebino_VLF_transmitter" title="Ebino VLF transmitter">Ebino</a> (Japan)</td> <td> </td></tr> <tr align="center" valign="top"> <td>RJH63 RJH66 <a href="/wiki/Vileyka_VLF_transmitter" title="Vileyka VLF transmitter">RJH69</a> RJH77 RJH99</td> <td>23 kHz</td> <td>various locations (Russia)</td> <td>Time signal transmitter Beta </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/VLF_transmitter_DHO38" title="VLF transmitter DHO38">DHO38</a></td> <td>23.4 kHz</td> <td>near <a href="/wiki/Rhauderfehn" title="Rhauderfehn">Rhauderfehn</a> (Germany)</td> <td>submarine communication </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/VLF_Transmitter_Cutler" title="VLF Transmitter Cutler">NAA</a></td> <td>24 kHz</td> <td><a href="/wiki/Cutler,_Maine" title="Cutler, Maine">Cutler, Maine</a> (USA)</td> <td>Used for submarine communication, at <span class="nowrap">2 megawatts</span><sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/Jim_Creek_Naval_Radio_Station" title="Jim Creek Naval Radio Station">NLK</a></td> <td>24.6 kHz</td> <td><a href="/wiki/Oso,_Washington" title="Oso, Washington">Oso, Washington</a> (USA)</td> <td>192 kW<sup id="cite_ref-Fidani-2011_16-4" class="reference"><a href="#cite_note-Fidani-2011-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </td></tr> <tr align="center" valign="top"> <td>NLF</td> <td>24.8 kHz</td> <td><a href="/wiki/Arlington,_Washington" title="Arlington, Washington">Arlington, Washington</a> (USA)</td> <td>Used for submarine communication.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> </td></tr> <tr align="center" valign="top"> <td>NML</td> <td>25.2 kHz</td> <td><a href="/wiki/LaMoure,_North_Dakota" title="LaMoure, North Dakota">LaMoure, North Dakota</a> (USA)</td> <td> </td></tr> <tr align="center" valign="top"> <td><a href="/wiki/PNS_Hameed" title="PNS Hameed">PNSH</a></td> <td>14–25.2? kHz</td> <td><a href="/wiki/Karachi_coast" class="mw-redirect" title="Karachi coast">Karachi coast</a>, <a href="/wiki/Sindh" title="Sindh">Sindh</a> (Pakistan)</td> <td> </td></tr> </tbody></table> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=17" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Communication_with_submarines" title="Communication with submarines">Communication with submarines</a></li> <li><a href="/wiki/OMEGA_Navigation_System" class="mw-redirect" title="OMEGA Navigation System">OMEGA Navigation System</a>, 1971–1997</li> <li><a href="/wiki/Radio_atmospheric" class="mw-redirect" title="Radio atmospheric">Radio atmospheric</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=18" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-ITU_Nomenclature-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-ITU_Nomenclature_1-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20131031020427/http://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-7-200005-I%21%21PDF-E.pdf">"Nomenclature of the frequency and wavelength bands used in telemmunications"</a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/ITU" class="mw-redirect" title="ITU">ITU</a>. Rec. ITU-R V.431-7. Archived from <a rel="nofollow" class="external text" href="http://www.itu.int/dms_pubrec/itu-r/rec/v/R-REC-V.431-7-200005-I!!PDF-E.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 31 October 2013<span class="reference-accessdate">. Retrieved <span class="nowrap">20 February</span> 2013</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Nomenclature+of+the+frequency+and+wavelength+bands+used+in+telemmunications&rft.pub=ITU&rft_id=http%3A%2F%2Fwww.itu.int%2Fdms_pubrec%2Fitu-r%2Frec%2Fv%2FR-REC-V.431-7-200005-I%21%21PDF-E.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></span> </li> <li id="cite_note-Hunsucker-2"><span class="mw-cite-backlink">^ <a href="#cite_ref-Hunsucker_2-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Hunsucker_2-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Hunsucker_2-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-Hunsucker_2-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFHunsuckerHargreaves2002" class="citation book cs1">Hunsucker, R.D.; Hargreaves, John Keith (2002). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=IQWHj2bgcxcC&pg=PA419"><i>The high-latitude ionosphere and its effects on radio propagation</i></a>. 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Retrieved <span class="nowrap">14 January</span> 2021</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Geosciences&rft.atitle=The+Central+Italy+Electromagnetic+Network+and+the+2009+L%27Aquila+earthquake%3A+Observed+electric+activity&rft.volume=1&rft.issue=1&rft.pages=3-25&rft.date=2011-12-08&rft.issn=2076-3263&rft_id=info%3Adoi%2F10.3390%2Fgeosciences1010003&rft_id=info%3Abibcode%2F2011Geosc...1....3F&rft.aulast=Fidani&rft.aufirst=Cristiano&rft_id=http%3A%2F%2Fwww.mdpi.com%2F2076-3263%2F1%2F1%2F3%2Fpdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.random-abstract.com/radio/">"Shortwave HF VHF UHF utilities monitoring"</a>. <i>Random Abstract</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Random+Abstract&rft.atitle=Shortwave+HF+VHF+UHF+utilities+monitoring&rft_id=http%3A%2F%2Fwww.random-abstract.com%2Fradio%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></span> </li> <li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="http://www.smh.com.au/news/travel/naval-base-link-to-qantas-plunge/2008/11/14/1226318890475.html">"Naval base link to jet plunge"</a>. <i><a href="/wiki/The_Sydney_Morning_Herald" title="The Sydney Morning Herald">The Sydney Morning Herald</a></i>. Sydney, AU. 14 November 2008<span class="reference-accessdate">. Retrieved <span class="nowrap">14 November</span> 2008</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+Sydney+Morning+Herald&rft.atitle=Naval+base+link+to+jet+plunge&rft.date=2008-11-14&rft_id=http%3A%2F%2Fwww.smh.com.au%2Fnews%2Ftravel%2Fnaval-base-link-to-qantas-plunge%2F2008%2F11%2F14%2F1226318890475.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></span> </li> <li id="cite_note-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-19">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.globalsecurity.org/military/facility/cutler.htm">"Cutler"</a>. <i>GlobalSecurity</i>. Military Facilities.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=GlobalSecurity&rft.atitle=Cutler&rft_id=http%3A%2F%2Fwww.globalsecurity.org%2Fmilitary%2Ffacility%2Fcutler.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.vlf.it/trond2/20-25khz.html">"20–25kHz"</a>. <i>vlf.it</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=vlf.it&rft.atitle=20%E2%80%9325kHz&rft_id=http%3A%2F%2Fwww.vlf.it%2Ftrond2%2F20-25khz.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span><sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citing_sources#What_information_to_include" title="Wikipedia:Citing sources"><span title="A complete citation is needed. (January 2021)">full citation needed</span></a></i>]</sup><br /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20110927004529/http://ludb.clui.org/ex/i/WA3248/">"WA3248"</a>. <i>ludb.clui.org</i>. Archived from <a rel="nofollow" class="external text" href="http://ludb.clui.org/ex/i/WA3248/">the original</a> on 2011-09-27<span class="reference-accessdate">. Retrieved <span class="nowrap">2009-07-13</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=ludb.clui.org&rft.atitle=WA3248&rft_id=http%3A%2F%2Fludb.clui.org%2Fex%2Fi%2FWA3248%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span><sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citing_sources#What_information_to_include" title="Wikipedia:Citing sources"><span title="A complete citation is needed. (January 2021)">full citation needed</span></a></i>]</sup></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=19" title="Edit section: Further reading"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRomero,_R.2006" class="citation book cs1 cs1-prop-foreign-lang-source">Romero, R. (2006). <i>Radio Natura</i> (in Italian). Albino, Italy: SANDIT S.r.l.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Radio+Natura&rft.place=Albino%2C+Italy&rft.pub=SANDIT+S.r.l.&rft.date=2006&rft.au=Romero%2C+R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKlawitter,_G.Oexner,_M.Herold,_K.2000" class="citation book cs1 cs1-prop-foreign-lang-source">Klawitter, G.; Oexner, M.; Herold, K. (2000). <i>Langwelle und Längstwelle</i> (in German). Meckenheim, DE: Siebel Verlag GmbH. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-3-89632-043-8" title="Special:BookSources/978-3-89632-043-8"><bdi>978-3-89632-043-8</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Langwelle+und+L%C3%A4ngstwelle&rft.place=Meckenheim%2C+DE&rft.pub=Siebel+Verlag+GmbH&rft.date=2000&rft.isbn=978-3-89632-043-8&rft.au=Klawitter%2C+G.&rft.au=Oexner%2C+M.&rft.au=Herold%2C+K.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFriese2006" class="citation web cs1">Friese (January 2006). <a rel="nofollow" class="external text" href="http://www.magnet-ferritantennen.de/assets/plugindata/poola/funkamateur012006.pdf">"Very low wave reception with ferrite antennas 5-50 kHz"</a> <span class="cs1-format">(PDF)</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Very+low+wave+reception+with+ferrite+antennas+5-50+kHz&rft.date=2006-01&rft.au=Friese&rft_id=http%3A%2F%2Fwww.magnet-ferritantennen.de%2Fassets%2Fplugindata%2Fpoola%2Ffunkamateur012006.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AVery+low+frequency" class="Z3988"></span></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Very_low_frequency&action=edit&section=20" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="http://www.lwca.org">Longwave club of America</a></li> <li><a rel="nofollow" class="external text" href="http://www.vlf.it">Radio waves below 22 kHz</a></li> <li><a rel="nofollow" class="external text" href="https://groups.io/g/VLF">VLF Discussion Group</a></li> <li>Tomislav Stimac, "<i><a rel="nofollow" class="external text" href="http://www.vlf.it/frequency/bands.html">Definition of frequency bands (VLF, ELF... etc.)</a></i>".</li> <li><a href="https://en.wikibooks.org/wiki/Electronics/VLF-reception_with_the_PC" class="extiw" title="b:Electronics/VLF-reception with the PC">PC-based VLF-reception</a></li> <li><a href="https://en.wikibooks.org/wiki/Electronics/Gallery_of_VLF-signals" class="extiw" title="b:Electronics/Gallery of VLF-signals">Gallery of VLF-signals</a></li> <li><a rel="nofollow" class="external text" href="http://spaceweather.com/glossary/inspire.html">NASA live streaming ELF -> VLF Receiver</a> NOTE: As of 05/03/2014, the "Listen live" links are down, but the site has some previously recorded examples to listen to.</li> <li><a rel="nofollow" class="external text" href="http://webflash.ess.washington.edu/">World Wide Lightning Location Network</a></li> <li><a rel="nofollow" class="external text" href="http://vlf.stanford.edu/research/introduction-vlf">Stanford University VLF group</a></li> <li><a rel="nofollow" class="external text" href="http://moondog.astro.louisville.edu/index.html">University of Louisville VLF Monitor</a></li> <li><a rel="nofollow" class="external text" href="http://www.vlfradio.com/">Larry's Very Low Frequency site</a></li> <li><a rel="nofollow" class="external text" href="http://www.markyd26uk.110mb.com/vlf.html">Mark's Live Online VLF Receiver, UK</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20090228212920/http://markyd26uk.110mb.com/vlf.html">Archived</a> 2009-02-28 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a></li> <li><a rel="nofollow" class="external text" href="http://www.qsl.net/iw0bzd/VLF_TUBE_RX.htm">IW0BZD VLF TUBE receiver</a></li> <li><a rel="nofollow" class="external text" href="http://www.ab9il.net/vlf/vlf1.html">Internet based VLF listening guide with server list</a></li> <li><a rel="nofollow" class="external text" href="http://sidstation.loudet.org/stations-list-en.xhtml">List of VLF-transmitters</a></li></ul> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output 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signal)">BPC</a></li> <li><a href="/wiki/BPL_(time_service)" title="BPL (time service)">BPL</a></li> <li><a href="/wiki/BSF_(time_service)" title="BSF (time service)">BSF</a></li> <li><a href="/wiki/Beta_(time_signal)" title="Beta (time signal)">Beta</a></li> <li><a href="/wiki/DCF77" title="DCF77">DCF77</a></li> <li><a href="/wiki/JJY" title="JJY">JJY</a></li> <li><a href="/wiki/RBU_(radio_station)" title="RBU (radio station)">RBU</a></li> <li><a href="/wiki/RTZ_(radio_station)" title="RTZ (radio station)">RTZ</a></li> <li><a href="/wiki/ALS162_time_signal" title="ALS162 time signal">TDF time signal</a></li> <li><a href="/wiki/Time_from_NPL_(MSF)" title="Time from NPL (MSF)">Time from NPL</a></li> <li><a href="/wiki/WWVB" title="WWVB">WWVB</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/High_frequency" title="High frequency">Shortwave</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" 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class="mw-redirect" title="Ultra-high frequency">UHF</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Radio_Data_System" title="Radio Data System">Radio Data System</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Satellite_navigation" title="Satellite navigation">Satellite</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/BeiDou" title="BeiDou">BeiDou</a></li> <li><a href="/wiki/DORIS_(satellite_system)" title="DORIS (satellite system)">DORIS</a></li> <li><a href="/wiki/GLONASS" title="GLONASS">GLONASS</a></li> <li><a href="/wiki/Galileo_(satellite_navigation)" title="Galileo (satellite navigation)">Galileo</a></li> <li><a href="/wiki/Global_Positioning_System" title="Global Positioning System">Global Positioning System</a></li> <li><a href="/wiki/Indian_Regional_Navigation_Satellite_System" title="Indian Regional Navigation Satellite System">IRNSS</a></li> <li><a href="/wiki/Quasi-Zenith_Satellite_System" title="Quasi-Zenith Satellite System">Quasi-Zenith Satellite System</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Defunct</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/BSF_(time_service)" title="BSF (time service)">BSF</a></li> <li><a href="/wiki/HBG_(time_signal)" title="HBG (time signal)">HBG</a></li> <li><a href="/wiki/NAA_(Arlington,_Virginia)" title="NAA (Arlington, Virginia)">NAA</a></li> <li><a href="/wiki/OLB5" title="OLB5">OLB5</a></li> <li><a href="/wiki/OMA_(time_signal)" title="OMA (time signal)">OMA</a></li> <li><a href="/wiki/Radio_VNG" title="Radio VNG">Radio VNG</a></li> <li><a href="/wiki/WWVB" title="WWVB">WWVL</a></li> <li><a href="/wiki/Y3S" title="Y3S">Y3S</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Radio_spectrum_(ITU)" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Radio_spectrum" title="Template:Radio spectrum"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Radio_spectrum" title="Template talk:Radio spectrum"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Radio_spectrum" title="Special:EditPage/Template:Radio spectrum"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Radio_spectrum_(ITU)" style="font-size:114%;margin:0 4em"><a href="/wiki/Radio_spectrum" title="Radio spectrum">Radio spectrum</a> (ITU)</div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0;background:transparent;color:inherit;"><div style="padding:0px"><table class="navbox-columns-table" style="border-spacing: 0px; text-align:left;width:auto; margin-left:auto; margin-right:auto;"><tbody><tr style="vertical-align:top"><td class="navbox-list" style="padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Extremely_low_frequency" title="Extremely low frequency">ELF</a></b> <br /> 3 Hz/100 Mm <br /> 30 Hz/10 Mm </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Super_low_frequency" title="Super low frequency">SLF</a></b> <br /> 30 Hz/10 Mm <br /> 300 Hz/1 Mm </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Ultra_low_frequency" title="Ultra low frequency">ULF</a></b> <br /> 300 Hz/1 Mm <br /> 3 kHz/100 km </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a class="mw-selflink selflink">VLF</a></b> <br /> 3 kHz/100 km <br /> 30 kHz/10 km </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Low_frequency" title="Low frequency">LF</a></b> <br /> 30 kHz/10 km <br /> 300 kHz/1 km </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Medium_frequency" title="Medium frequency">MF</a></b> <br /> 300 kHz/1 km <br /> 3 MHz/100 m </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/High_frequency" title="High frequency">HF</a></b> <br /> 3 MHz/100 m <br /> 30 MHz/10 m </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Very_high_frequency" title="Very high frequency">VHF</a></b> <br /> 30 MHz/10 m <br /> 300 MHz/1 m </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Ultra_high_frequency" title="Ultra high frequency">UHF</a></b> <br /> 300 MHz/1 m <br /> 3 GHz/100 mm </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Super_high_frequency" title="Super high frequency">SHF</a></b> <br /> 3 GHz/100 mm <br /> 30 GHz/10 mm </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Extremely_high_frequency" title="Extremely high frequency">EHF</a></b> <br /> 30 GHz/10 mm <br /> 300 GHz/1 mm </p> </div></td><td class="navbox-list" style="border-left:2px solid #fdfdfd;padding:0px;text-align:center;width:10em;"><div> <p><b><a href="/wiki/Tremendously_high_frequency" class="mw-redirect" title="Tremendously high frequency">THF</a></b> <br /> 300 GHz/1 mm <br /> 3 THz/0.1 mm </p> </div></td></tr></tbody></table></div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div><b><span class="nowrap"><span class="noviewer" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/commons/1/1d/Radio_icon.png" decoding="async" width="32" height="23" class="mw-file-element" data-file-width="30" data-file-height="22" /></span></span> </span><a href="/wiki/Portal:Radio" title="Portal:Radio">Radio portal</a></b></div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"><style data-mw-deduplicate="TemplateStyles:r886047488">.mw-parser-output .nobold{font-weight:normal}</style></div><div role="navigation" class="navbox" aria-labelledby="Electromagnetic_spectrum" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Electromagnetic_spectrum" title="Template:Electromagnetic spectrum"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Electromagnetic_spectrum" title="Template talk:Electromagnetic spectrum"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Electromagnetic_spectrum" title="Special:EditPage/Template:Electromagnetic spectrum"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Electromagnetic_spectrum" style="font-size:114%;margin:0 4em"><a href="/wiki/Electromagnetic_spectrum" title="Electromagnetic spectrum">Electromagnetic spectrum</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2" style="padding:0.3em 0.5em 0.4em;line-height:1.25em;font-weight:bold;"><div> <ul><li><a href="/wiki/Gamma_ray" title="Gamma ray">Gamma rays</a></li> <li><a href="/wiki/X-ray" title="X-ray">X-rays</a></li> <li><a href="/wiki/Ultraviolet" title="Ultraviolet">Ultraviolet</a></li> <li><a href="/wiki/Visible_spectrum" title="Visible spectrum">Visible</a></li> <li><a href="/wiki/Infrared" title="Infrared">Infrared</a></li> <li><a href="/wiki/Microwave" title="Microwave">Microwave</a></li> <li><a href="/wiki/Radio_wave" title="Radio wave">Radio</a><figure class="mw-halign-center" typeof="mw:File"><a href="/wiki/File:Frequency_vs._wave_length.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/62/Frequency_vs._wave_length.svg/500px-Frequency_vs._wave_length.svg.png" decoding="async" width="500" height="65" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/62/Frequency_vs._wave_length.svg/750px-Frequency_vs._wave_length.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/62/Frequency_vs._wave_length.svg/1000px-Frequency_vs._wave_length.svg.png 2x" data-file-width="800" data-file-height="104" /></a><figcaption></figcaption></figure><div style="clear:both;" class=""></div><span class="nobold"><i><span style="font-size:120%">←</span> higher <a href="/wiki/Frequency" title="Frequency">frequencies</a><span class="nowrap">       </span>longer <a href="/wiki/Wavelength" title="Wavelength">wavelengths</a> <span style="font-size:120%">→</span></i></span></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Gamma_ray" title="Gamma ray">Gamma rays</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Very-high-energy_gamma_ray" title="Very-high-energy gamma ray">Very-high-energy gamma ray</a></li> <li><a href="/wiki/Ultra-high-energy_gamma_ray" title="Ultra-high-energy gamma ray">Ultra-high-energy gamma ray</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/X-ray" title="X-ray">X-rays</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Soft_X-ray" class="mw-redirect" title="Soft X-ray">Soft X-ray</a></li> <li><a href="/wiki/Hard_X-ray" class="mw-redirect" title="Hard X-ray">Hard X-ray</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Ultraviolet" title="Ultraviolet">Ultraviolet</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Extreme_ultraviolet" title="Extreme ultraviolet">Extreme ultraviolet</a></li> <li><a href="/wiki/Vacuum_ultraviolet" class="mw-redirect" title="Vacuum ultraviolet">Vacuum ultraviolet</a></li> <li><a href="/wiki/Lyman-alpha" title="Lyman-alpha">Lyman-alpha</a></li> <li><a href="/wiki/Far_ultraviolet" class="mw-redirect" title="Far ultraviolet">FUV</a></li> <li><a href="/wiki/Middle_ultraviolet" class="mw-redirect" title="Middle ultraviolet">MUV</a></li> <li><a href="/wiki/Near_ultraviolet" class="mw-redirect" title="Near ultraviolet">NUV</a></li> <li><a href="/wiki/Ultraviolet_C" class="mw-redirect" title="Ultraviolet C">UVC</a></li> <li><a href="/wiki/Ultraviolet_B" class="mw-redirect" title="Ultraviolet B">UVB</a></li> <li><a href="/wiki/Ultraviolet_A" class="mw-redirect" title="Ultraviolet A">UVA</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Visible_spectrum" title="Visible spectrum">Visible (optical)</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Violet_(color)" title="Violet (color)">Violet</a></li> <li><a href="/wiki/Blue" title="Blue">Blue</a></li> <li><a href="/wiki/Cyan" title="Cyan">Cyan</a></li> <li><a href="/wiki/Green" title="Green">Green</a></li> <li><a href="/wiki/Yellow" title="Yellow">Yellow</a></li> <li><a href="/wiki/Orange_(colour)" title="Orange (colour)">Orange</a></li> <li><a href="/wiki/Red" title="Red">Red</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Infrared" title="Infrared">Infrared</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Near-infrared" class="mw-redirect" title="Near-infrared">NIR</a> (<a href="/wiki/Photometric_system" title="Photometric system">Bands</a>: <a href="/wiki/J_band_(infrared)" title="J band (infrared)">J</a>, <a href="/wiki/K_band_(infrared)" title="K band (infrared)">K</a>, <a href="/wiki/H_band_(infrared)" title="H band (infrared)">H</a>)</li> <li><a href="/wiki/Infrared#Regions" title="Infrared">SWIR</a></li> <li><a href="/wiki/Infrared#Regions" title="Infrared">MWIR</a> (<a href="/wiki/Photometric_system" title="Photometric system">Bands</a>: <a href="/wiki/L_band_(infrared)" title="L band (infrared)">L</a>, <a href="/wiki/M_band_(infrared)" title="M band (infrared)">M</a>, <a href="/wiki/N_band" title="N band">N</a>)</li> <li><a href="/wiki/Infrared#Regions" title="Infrared">LWIR</a></li> <li><a href="/wiki/Far_infrared" title="Far infrared">FIR</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Microwave" title="Microwave">Microwaves</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/W_band" title="W band">W band</a></li> <li><a href="/wiki/V_band" title="V band">V band</a></li> <li><a href="/wiki/Q_band" title="Q band">Q band</a></li> <li><a href="/wiki/Ka_band" title="Ka band">K<sub>a</sub> band</a></li> <li><a href="/wiki/K_band_(IEEE)" title="K band (IEEE)">K band</a></li> <li><a href="/wiki/Ku_band" title="Ku band">K<sub>u</sub> band</a></li> <li><a href="/wiki/X_band" title="X band">X band</a></li> <li><a href="/wiki/C_band_(IEEE)" title="C band (IEEE)">C band</a></li> <li><a href="/wiki/S_band" title="S band">S band</a></li> <li><a href="/wiki/L_band" title="L band">L band</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Radio_frequency" title="Radio frequency">Radio</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Terahertz_radiation" title="Terahertz radiation">THF</a></li> <li><a href="/wiki/Extremely_high_frequency" title="Extremely high frequency">EHF</a></li> <li><a href="/wiki/Super_high_frequency" title="Super high frequency">SHF</a></li> <li><a href="/wiki/Ultra_high_frequency" title="Ultra high frequency">UHF</a></li> <li><a href="/wiki/Very_high_frequency" title="Very high frequency">VHF</a></li> <li><a href="/wiki/High_frequency" title="High frequency">HF</a></li> <li><a href="/wiki/Medium_frequency" title="Medium frequency">MF</a></li> <li><a href="/wiki/Low_frequency" title="Low frequency">LF</a></li> <li><a class="mw-selflink selflink">VLF</a></li> <li><a href="/wiki/Ultra_low_frequency" title="Ultra low frequency">ULF</a></li> <li><a href="/wiki/Super_low_frequency" title="Super low frequency">SLF</a></li> <li><a href="/wiki/Extremely_low_frequency" title="Extremely low frequency">ELF</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;background:lavender;"><a href="/wiki/Wavelength" title="Wavelength">Wavelength</a> types</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Microwave" title="Microwave">Microwave</a></li> <li><a href="/wiki/Shortwave_radio" title="Shortwave radio">Shortwave</a></li> <li><a href="/wiki/Medium_wave" title="Medium wave">Medium wave</a></li> <li><a href="/wiki/Longwave" title="Longwave">Longwave</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"><style data-mw-deduplicate="TemplateStyles:r1038841319">.mw-parser-output .tooltip-dotted{border-bottom:1px dotted;cursor:help}</style></div><div role="navigation" class="navbox authority-control" aria-label="Navbox" style="padding:3px"><table class="nowraplinks hlist navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Help:Authority_control" title="Help:Authority control">Authority control databases</a>: National <span class="mw-valign-text-top 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