RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 1 ADF OPERATIONS Aim: To learn the principles behind the operation of the ADF navigation system. Application: - orientation (where am I?). - supplementary navigation information. Definitions: NDB - Non-Directional Beacon, is the ground radio transmitter that radiates energy in all directions. ADF - Automatic Direction Finder, is the airborne receiver which when tuned, indicates the direction TO the NDB. Locator - Low powered NDB used for approaches in conjunction with an ILS. Principles: NDB - Operates on frequencies between 200Hz and 500 KHz (LF to MF radio range). - Primarily short distance navigation aids of usually < 200Nm. - Transmitter power is between 100 and 3000W with majority in the 100 to 500W range. - Greater the transmitter power, the greater the range. - Details found in ERSA and ERC charts; VTC, TAC and VNC. - The emitted wave has a Morse code identifier superimposed upon it, of 2 to 3 letters. - The carrier wave may Also contain voice/ ATIS information. ADF - airborne equipment consists of three main components: 1. Antennae - loop antenna aligns itself perpendicular to the direction of the received signal. As it is a loop, two nulls are received - one removed 180 from the other. - to resolve the ambiguity the signal from the sense antenna is combined, to drive the loop (and hence the pointer) in the correct direction. RMIT Flight Training ADF Operations Brief 18 RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 2 2. Receiver - the receiver and associated control panel are used to tune the ADF to the required NDB. OFF = switch ADF off ADF = normal position for bearing information ANT = only sense antenna is used. No bearing information but enhanced audio reception BFO = beat frequency oscillator, rarely used in Australia TEST = deflects needle to right wing. Pressing ADF again points needle to NDB 3. Cockpit Display - the needle always points directly TO the station. 4. Fixed-Card ADF - the needle indicates relative bearing of the station from the aircraft Rotatable-Card ADF - the needle indicates a magnetic bearing TO the station. Any change in HDG requires re-alignment of the ADF card. Radio Magnetic Indicator (RMI) - is a gyro-stabilised ADF which automatically aligns the card, and indicates magnetic bearings. RMIT Flight Training ADF Operations Brief 18 RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 3 Considerations: Limitations - various limitations effect the readings of the ADF: a) Coastal Refraction - when passing from land to sea at an oblique angle, NDB radio waves may be refracted (bent) due to different conducting and reflecting properties of land and water. Always refracts towards the land (away from the normal). b) Co-Channel Interference - signals received from other NDBs operating on the same frequency, may give false bearing information. (eg: SHT and BNS) Generally NDBs of similar frequencies are spaced well apart geographically. c) Thunderstorm Effect - thunderstorms generate a lot of radio energy, and the ADF needle may point towards it; a poor mans weather radar. d) Terrain Effect - radio signals have greater range over water than over sandy or mountainous country where the range is considerably reduced. Brief 18 RMIT Flight Training ADF Operations RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 4 e) Mountain Effect - fluctuating bearings may result from the mixing of radio waves reflected from the surfaces of mountains. - higher frequencies minimise this effect. f) Night Effect - radio waves take two paths; ground waves (along the Earth’s surface) and sky waves. - during the day the sky waves are absorbed by the lower ionosphere. At night the ionosphere reflects the sky wave back, mixing with the ground wave, causing errors. g) Quadrantal Error - results from the metal construction of the aircraft. Needle of ADF will align itself to the cardinal points of aircraft. (ie: N, E, S, W) when station in between these quadrants. Brief 18 RMIT Flight Training ADF Operations RMIT Instructor Rating Mass Briefs Issue 1 /2004 Page 5 Air Exercise: T - Tune to NDB using receiver I - Identify using Morse code T - Test by depressing TEST switch Airmanship: - Always use NDB within it’s rated coverage - TIT checks before use - AM stations not to be used for navigation - Instrument taxi checks to be completed Brief 18 RMIT Flight Training ADF Operations作者: 猪也能飞 时间: 2013-10-28 19:29:02