{"id":14518,"date":"2025-06-07T16:29:36","date_gmt":"2025-06-07T10:59:36","guid":{"rendered":"https:\/\/ibexaviation.com\/pilot-training\/?p=14518"},"modified":"2025-07-20T07:31:06","modified_gmt":"2025-07-20T02:01:06","slug":"vhf-direction-finder","status":"publish","type":"post","link":"https:\/\/ibexaviation.com\/pilot-training\/vhf-direction-finder\/","title":{"rendered":"VHF Direction Finder (VDF)"},"content":{"rendered":"\n<h2>VHF Direction Finder<\/h2>\n\n\n\n<h3>Introduction to VDF<\/h3>\n\n\n\n<ul><li>VDF is a ground based equipment used in Air Traffic Control to find the bearing of aircrafts<\/li><li>Bearing accuracy of VDF is up to half a degree however range information is not available<\/li><li>VDF works in the VHF band with frequencies range between 118 to 137 MHz<\/li><li>Loop antenna principle is used to find the direction of transmission where the transmission from an aircraft from a perpendicular direction to the loop ariel gives zero phase difference<\/li><li>Rotating loop is replaced by electronically rotated fixed vertical elements<\/li><li>Adcock ariel is an advanced form of electronic rotating ariel which uses doppler effect to resolve the bearing of transmission<\/li><\/ul>\n\n\n\n<h3>Introduction to Q Codes<\/h3>\n\n\n\n<ul><li>A VDF station can provide QDR, QDM, QTE and QUJ on request from aircraft<\/li><li>QDR or Radial is the aircraft\u00e2\u20ac\u2122s Magnetic bearing from the station<\/li><li>QDM is the reciprocal of QDR which is is the magnetic heading to steer to reach over the VDF in nil wind<\/li><li>QTE is the true bearing from the station while QUJ is the true bearing to the station<\/li><\/ul>\n\n\n\n<h3>Range and Accuracy of VDF<\/h3>\n\n\n\n<ul><li>Maximum range of VDF is governed by line of sight formula<\/li><li>VDF range is further constrained by terrain, meteorological conditions and power of transmission<\/li><li>VDF readings are graded as Class A, B, C and D based on accuracies<\/li><li>Accuracies of A, B, C, D are 2, 5, 10 and greater than 10 degrees<\/li><li>VDF accuracies reduce due to Site Error, Synchronous Transmission, Attitude of aircraft and Multi Path Fading<\/li><li>Site error occurs due to reflection from buildings while Synchronous Transmission is due to two or more aircrafts transmitting in close proximity<\/li><li>Aircrafts flying at other straight and level attitude like climb, descend or during turns results in erroneous readings<\/li><li>Flight close to overhead the VDF ground facility may result in error due to Multi-path fading<\/li><\/ul>\n\n\n\n<h3>Position Fix using Triangulation of VDF Bearings<\/h3>\n\n\n\n<ul><li>Triangulation by a network of two or more VDF ground stations is provided to aircraft using distress frequency of 121.5 MHz<\/li><li>ATC equipped with VDF coordinate to triangulate and provide position fix for aircraft in distress or lost<\/li><li>Distress aircrafts are provided with Magnetic tracks to station (QDM) or calculated headings and height to fly (QGH)<\/li><\/ul>\n\n\n\n<h2>Best of luck<\/h2>\n","protected":false},"excerpt":{"rendered":"<p>VHF Direction Finder Introduction to VDF VDF is a ground based equipment used in Air Traffic Control to find the bearing of aircrafts Bearing accuracy of VDF is up to half a degree however range information is not available VDF works in the VHF band with frequencies range between 118 to 137 MHz Loop antenna principle is used to find the direction of transmission where the transmission from an aircraft from a perpendicular direction to the loop ariel gives zero phase difference Rotating loop is replaced by electronically rotated fixed&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},"categories":[326],"tags":[],"_links":{"self":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14518"}],"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=14518"}],"version-history":[{"count":0,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/posts\/14518\/revisions"}],"wp:attachment":[{"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/media?parent=14518"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/categories?post=14518"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ibexaviation.com\/pilot-training\/wp-json\/wp\/v2\/tags?post=14518"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}