{"id":14522,"date":"2025-06-07T16:31:05","date_gmt":"2025-06-07T11:01:05","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14522"},"modified":"2026-07-26T09:55:17","modified_gmt":"2026-07-26T04:25:17","slug":"vhf-omni-directional-radio-range","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/vhf-omni-directional-radio-range\/","title":{"rendered":"VHF Omni Directional Radio Range (VOR)"},"content":{"rendered":"<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-1.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<h2>Direction Measurement using Very High Frequency Omni-Directional Radio Range (VOR)<\/h2>\n<p>VOR (VHF Omnidirectional Range) is a radio navigation system that provides aircraft with accurate directional guidance. It helps pilots determine their bearing (radial) from a VOR ground station. VOR is widely used for en-route navigation and instrument flight procedures.<\/p>\n<h3>Introduction to VOR<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-2.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Very High Frequency Omni-Directional Radio Range (VOR) is a short-range radio navigation aid approved by ICAO.<\/li>\n<li>VOR is largely free from static interference and night effect, making it suitable for both day and night operations.<\/li>\n<li>VOR determines aircraft bearing using the principle of <strong>phase comparison<\/strong>.<\/li>\n<li>The station simultaneously transmits a <strong>Reference Signal<\/strong> and a <strong>Variable Signal<\/strong>.<\/li>\n<li>The phase difference between these signals determines the aircraft&#8217;s radial.<\/li>\n<li>Aircraft equipment consists of a VHF dipole antenna and a VOR receiver.<\/li>\n<li>VOR information is displayed on the <strong>Radio Magnetic Indicator (RMI)<\/strong> and <strong>Course Deviation Indicator (CDI)<\/strong>.<\/li>\n<\/ul>\n<h3>VOR Transmission<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-3.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>VOR transmits magnetic bearings known as <strong>radials<\/strong>.<\/li>\n<li>There are <strong>360 radials<\/strong>, each separated by <strong>1\u00b0<\/strong>.<\/li>\n<li>VOR transmits horizontally polarised VHF radio waves.<\/li>\n<li>Operating frequencies range from <strong>108.00 MHz to 117.95 MHz<\/strong>.<\/li>\n<li>VOR frequencies use even first decimal digits (e.g., <strong>108.60 MHz<\/strong>).<\/li>\n<li>Each station broadcasts a unique three-letter Morse code identification or station name.<\/li>\n<li>The identification is transmitted at least <strong>seven times per minute<\/strong>.<\/li>\n<li>ATIS or a continuous tone may replace the Morse identification.<\/li>\n<\/ul>\n<h3>Emission Designator<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-4.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The emission designator for VOR is <strong>A9W<\/strong>.<\/li>\n<li><strong>A<\/strong> \u2013 Double-sideband amplitude modulation.<\/li>\n<li><strong>9<\/strong> \u2013 Composite modulation system.<\/li>\n<li><strong>W<\/strong> \u2013 Telemetry or transmission of measured information.<\/li>\n<\/ul>\n<h3>Principle of VOR<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-5.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>VOR determines bearing by comparing the phase of the Reference and Variable signals.<\/li>\n<li>The combined radiation pattern forms a <strong>Limacon<\/strong>.<\/li>\n<li>The Reference Signal is a constant-phase, omnidirectional <strong>30 Hz frequency-modulated<\/strong> signal.<\/li>\n<li>The Variable Signal is a <strong>30 Hz amplitude-modulated<\/strong> signal whose phase changes as the Limacon rotates.<\/li>\n<li>The airborne receiver measures the phase difference between the two signals.<\/li>\n<li>At Magnetic North, the Reference and Variable signals are in phase.<\/li>\n<li>The measured phase difference corresponds to the aircraft&#8217;s magnetic bearing (radial).<\/li>\n<\/ul>\n<h3>Doppler VOR (DVOR)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-6.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Doppler VOR minimises site errors caused by uneven terrain and ground reflections.<\/li>\n<li>A DVOR uses a circular array approximately <strong>13.4 m<\/strong> in diameter with <strong>48 transmitting elements<\/strong>.<\/li>\n<li>The Variable Signal is frequency modulated to create the Doppler effect.<\/li>\n<li>This method produces less interference than conventional amplitude modulation.<\/li>\n<li>An electronically rotating antenna produces the required phase shift.<\/li>\n<li>The antenna rotates electronically at approximately <strong>30 revolutions per second<\/strong>.<\/li>\n<li>The airborne receiver measures phase differences to determine the selected radial.<\/li>\n<\/ul>\n<h2>Range and Accuracy of VOR<\/h2>\n<h3>Designated Operational Coverage (DOC)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-7.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The maximum theoretical range is determined by the line-of-sight principle.<\/li>\n<li>Actual range also depends on transmitter power.<\/li>\n<li>The inverse square law governs transmission power requirements.<\/li>\n<li>Designated Operational Coverage (DOC) is the protected service area around a VOR.<\/li>\n<li>DOC prevents interference from nearby VOR stations operating on the same frequency.<\/li>\n<li>DOC is expressed as <strong>Distance\/Altitude<\/strong>.<\/li>\n<li><strong>DOC 50\/25<\/strong> indicates service up to <strong>50 NM<\/strong> and <strong>2,500 ft<\/strong>.<\/li>\n<li>Different DOC values exist for Terminal, Low Altitude, and High Altitude VORs.<\/li>\n<\/ul>\n<h3>Accuracy of VOR<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-8.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Overall VOR accuracy depends on both ground station and airborne equipment.<\/li>\n<li>Proper site selection limits beacon error to less than <strong>1\u00b0<\/strong>.<\/li>\n<li>Doppler VOR significantly reduces site errors.<\/li>\n<li>Airborne receiver error is normally limited to less than <strong>3\u00b0<\/strong>.<\/li>\n<li>Total system error is generally limited to less than <strong>5\u00b0<\/strong>.<\/li>\n<\/ul>\n<h3>VOR Monitoring Equipment<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-9.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The station identification is automatically removed whenever system errors exceed permissible limits.<\/li>\n<li>Conditions that trigger shutdown include:<\/li>\n<ul>\n<li>Radial transmission error greater than <strong>1\u00b0<\/strong>.<\/li>\n<li>Transmitter power loss greater than <strong>15%<\/strong>.<\/li>\n<li>Failure of the ground monitoring equipment.<\/li>\n<\/ul>\n<li>The aircraft indicator displays a red or yellow warning flag whenever VOR information becomes unreliable.<\/li>\n<\/ul>\n<h3>Cone of Ambiguity (Cone of Confusion)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-10.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The airspace directly above a VOR station is known as the <strong>Cone of Ambiguity<\/strong> or <strong>Cone of Confusion<\/strong>.<\/li>\n<li>Within this region, VOR indications fluctuate and become unreliable.<\/li>\n<li>ICAO limits the cone to approximately <strong>40\u00b0 elevation<\/strong>.<\/li>\n<li>In practice, unreliable indications rarely extend beyond about <strong>80\u00b0 elevation<\/strong>.<\/li>\n<\/ul>\n<h3>Airway Navigation Using VOR<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-11.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>Typical VOR system accuracy is approximately <strong>\u00b15\u00b0<\/strong>.<\/li>\n<li>Standard airway width is <strong>10 NM<\/strong> (5 NM on either side of the centreline).<\/li>\n<li>According to the 1-in-60 rule, a 5\u00b0 error corresponds to approximately 5 NM at 60 NM.<\/li>\n<li>Airways normally have VOR stations spaced approximately <strong>120 NM<\/strong> apart.<\/li>\n<li>This ensures aircraft remain within acceptable navigation accuracy.<\/li>\n<\/ul>\n<h3>Types of VOR<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-12.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li><strong>CVOR<\/strong> \u2013 Conventional VOR used along airways.<\/li>\n<li><strong>BVOR<\/strong> \u2013 Broadcast VOR providing weather and airfield information.<\/li>\n<li><strong>DVOR<\/strong> \u2013 Doppler VOR designed to minimize site errors.<\/li>\n<li><strong>TVOR<\/strong> \u2013 Terminal VOR with reduced power for airport operations.<\/li>\n<li><strong>VOT<\/strong> \u2013 Test VOR used to verify airborne VOR equipment.<\/li>\n<li>During a VOT test, airborne equipment should indicate <strong>360\u00b0 \u00b14\u00b0<\/strong>.<\/li>\n<li><strong>VORTAC<\/strong> \u2013 A co-located VOR and TACAN station.<\/li>\n<li><strong>DBVORTAC<\/strong> \u2013 Combination of DVOR, BVOR, and VORTAC facilities.<\/li>\n<\/ul>\n<h2>Cockpit Indications of VOR on RMI, CDI and HSI<\/h2>\n<h3>Radio Magnetic Indicator (RMI)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-13.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Radio Magnetic Indicator (RMI) displays magnetic bearings from both NDB and VOR.<\/li>\n<li>The head of the pointer indicates <strong>QDM<\/strong> (bearing to the station).<\/li>\n<li>The tail of the pointer indicates <strong>QDR<\/strong> (bearing from the station).<\/li>\n<li>The ADF pointer converts relative bearings into magnetic bearings.<\/li>\n<li>The VOR pointer displays magnetic radials directly.<\/li>\n<\/ul>\n<h3>Course Deviation Indicator (CDI)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-14.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Course Deviation Indicator (CDI), also called the <strong>Omni Bearing Indicator (OBI)<\/strong>, displays deviation from a selected radial.<\/li>\n<li>The desired course is selected using the <strong>Omni Bearing Selector (OBS)<\/strong>.<\/li>\n<li>The CDI is used to intercept and maintain a selected VOR radial.<\/li>\n<li>The deviation bar always points toward the selected course.<\/li>\n<li>The <strong>TO\/FROM<\/strong> indicator shows whether the selected course leads toward or away from the station.<\/li>\n<li>In VOR mode, the CDI provides approximately <strong>10\u00b0<\/strong> of full-scale deflection on each side.<\/li>\n<li>On a five-dot indicator, each dot represents approximately <strong>2\u00b0<\/strong>.<\/li>\n<li>The CDI provides left\/right course guidance without considering aircraft heading.<\/li>\n<\/ul>\n<h3>Horizontal Situation Indicator (HSI)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-15.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Horizontal Situation Indicator (HSI) combines heading and navigation information into a single display.<\/li>\n<li>It displays the selected magnetic track or radial.<\/li>\n<li>It indicates deviation from the selected VOR course.<\/li>\n<li>It simultaneously displays aircraft heading and required heading.<\/li>\n<li>The HSI provides intuitive left\/right steering commands that account for aircraft heading.<\/li>\n<\/ul>\n<h3>Electronic Horizontal Situation Indicator (EHSI)<\/h3>\n<p> <img decoding=\"async\" src=\"https:\/\/ibexaviation.com\/page-show\/radio-navigation\/r7-vhf-omni-directional-radio-range-16.jpg\" alt=\"\" loading=\"lazy\"\/><\/p>\n<ul>\n<li>The Electronic Horizontal Situation Indicator (EHSI) provides additional navigation information.<\/li>\n<li>Displays terrain and weather information from the Airborne Weather Radar.<\/li>\n<li>Displays terrain proximity warnings from the Terrain Collision Avoidance System (TCAS\/TAWS, depending on installation).<\/li>\n<li>Displays distance information from Distance Measuring Equipment (DME).<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Direction Measurement using Very High Frequency Omni-Directional Radio Range (VOR) VOR (VHF Omnidirectional Range) is a radio navigation system that provides aircraft with accurate directional guidance. It helps pilots determine their bearing (radial) from a VOR ground station. VOR is widely used for en-route navigation and instrument flight procedures. Introduction to VOR Very High Frequency Omni-Directional Radio Range (VOR) is a short-range radio navigation aid approved by ICAO. VOR is largely free from static interference and night effect, making it suitable for both day and night operations. VOR determines aircraft&hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"disable_featured_image":false,"footnotes":""},"categories":[326],"tags":[],"class_list":["post-14522","post","type-post","status-publish","format-standard","hentry","category-cpl-atpl-radio-navigation"],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14522","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/comments?post=14522"}],"version-history":[{"count":2,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14522\/revisions"}],"predecessor-version":[{"id":16601,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14522\/revisions\/16601"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14522"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14522"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14522"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}