Radio navigation
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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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Radio navigation

RADIO NAVIGATION


The exam

The Exam!

  • Time: 1hr 30min

  • 59 questions

  • Day 3, i.e. Wednesday, 11:15

  • 75% pass mark


Direction finding

DIRECTION FINDING

General Principles


Vhf direction finding vdf

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


Df general principles

DF - General Principles

  • Radio waves travel along great circle routes


Df general principles1

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


Radio navigation

LOOP ANTENNA

NULL

Maximum

Signal Strength

Maximum

Signal Strength

NULL


Adcock vdf aerial

Adcock VDF Aerial


Radio navigation

Doppler Direction Finder


Ground station

Ground Station


Vdf crt display

VDF CRT Display


Radio navigation

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


Classification of bearings

Class A

Class B

Class C

Class D

± 2º

± 5º

± 10º

accuracy less than Class C

Classification of Bearings


Example of r t phraseology

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


Vdf approach

VDF Approach

= Pilot interpreted procedure

QGH procedure = Controller interpreted


Range errors

Range & Errors

  • VHF propagation = Line of Sight

    • Approximate MTR = FLx 12

  • Terrain

  • Atmospheric Refraction:

    • Super-refraction

    • Sub-refraction

  • Transmitter Power

  • Multi-path reflections


  • Synchronous transmissions

    Synchronous Transmissions

    Vector addition of signals


    Range errors1

    Range & Errors

    • Adverse polarisation:

    • Ground transmissions are vertically polarised

    • Best results obtained when aircraft is flying straight and level


    Questions

    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


    Questions1

    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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