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RADIO NAVIGATION
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The Exam! Time: 1hr 30min 59 questions Day 3, i.e. Wednesday, 11:15
75% pass mark
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DIRECTION FINDING General Principles
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VHF Direction Finding (VDF)
Service available to aircraft using VHF A/G Comms Frequency range = MHz Uses line-of-sight transmission from the aircraft to the ground station
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DF - General Principles
Radio waves travel along great circle routes
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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
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LOOP ANTENNA NULL Maximum Signal Strength Maximum Signal Strength NULL
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Adcock VDF Aerial
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Doppler Direction Finder
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Ground Station
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VDF CRT Display
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Magnetic bearing to the station True bearing from the station
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
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Classification of Bearings
Class A Class B Class C Class D ± 2º ± 5º ± 10º accuracy less than Class C
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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
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VDF Approach = Pilot interpreted procedure
QGH procedure = Controller interpreted
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Range & Errors VHF propagation = Line of Sight Terrain
Approximate MTR = FL x 12 Terrain Atmospheric Refraction: Super-refraction Sub-refraction Transmitter Power Multi-path reflections
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Synchronous Transmissions
Vector addition of signals
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Range & Errors Adverse polarisation:
Ground transmissions are vertically polarised Best results obtained when aircraft is flying straight and level
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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
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Questions Is a QGH procedure pilot or 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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