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RADIO NAVIGATION

RADIO NAVIGATION. The Exam!. Time: 1hr 30min 59 questions Day 3, i.e. Wednesday, 11:15. 75% pass mark. DIRECTION FINDING. General Principles. VHF Direction Finding (VDF). Service available to aircraft using VHF A/G Comms Frequency range = 118.00 - 137.00 MHz

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RADIO NAVIGATION

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  1. RADIO NAVIGATION

  2. The Exam! • Time: 1hr 30min • 59 questions • Day 3, i.e. Wednesday, 11:15 • 75% pass mark

  3. DIRECTION FINDING General Principles

  4. VHF Direction Finding (VDF) • Service available to aircraft using VHF A/G Comms • Frequency range = 118.00 - 137.00 MHz • Uses line-of-sight transmission from the aircraft to the ground station

  5. DF - General Principles • Radio waves travel along great circle routes

  6. DF - General Principles • An aerial used to detect the direction of a radio wave is known as a loop antenna • With an AM transmission, the antenna is energised by the Carrier Wave portion of the signal • The polar diagram for a loop antenna is a figure of eight

  7. LOOP ANTENNA NULL Maximum Signal Strength Maximum Signal Strength NULL

  8. Adcock VDF Aerial

  9. Doppler Direction Finder

  10. Ground Station

  11. VDF CRT Display

  12. Types of Bearings Red = Magnetic Blue = True QDR QTE QDM QUJ • QDM • QTE • QDR • QUJ • Magnetic bearing to the station • True bearing from the station • Magnetic bearing from the station • True bearing to the station

  13. Class A Class B Class C Class D ± 2º ± 5º ± 10º accuracy less than Class C Classification of Bearings

  14. Example of R/T Phraseology • “Walden Homer G-ABCD Request QDM G-ABCD” • “G-ABCD Walden Homer QDM 245 degrees, Class Bravo” • “245 degrees, Class Bravo, G-ABCD” Refer to Communications notes

  15. VDF Approach = Pilot interpreted procedure QGH procedure = Controller interpreted

  16. Range & Errors • VHF propagation = Line of Sight • Approximate MTR = FLx 12 • Terrain • Atmospheric Refraction: • Super-refraction • Sub-refraction • Transmitter Power • Multi-path reflections

  17. Synchronous Transmissions Vector addition of signals

  18. Range & Errors • Adverse polarisation: • Ground transmissions are vertically polarised • Best results obtained when aircraft is flying straight and level

  19. Questions • In which frequency range is VHF DF available? • 118 – 137 MHz • What part of the aircraft transmission does the ground equipment respond to? • The carrier wave • What is the accuracy of a Class A bearing? • ± 2º

  20. Questions • Is a QGH procedure pilot or controller interpreted? • Controller interpreted • A true bearing to the aircraft from the station is a Q..? • QTE • A magnetic bearing to the aircraft from the station is a Q..? • QDR

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