02 VDF

Question 1

How does VDF work?

Answer 1

DF uses a radio signal from an airborne VHF radio transmitter to determine the direction of an incoming radio signal.

Question 2

Single aerodrome VDF?

Answer 2

A VDF line of position from a single aerodrome provides a bearing only.

Question 3

UK fixing service?

Answer 3

Some countries provide a position fixing service using more than one ground station (e.g., 121.500 MHz in the UK).

If two VHF direction finders are installed at sufficient distance from each other, they allow the ATC system to triangulate the position of a VHF transmission.

Question 4

VDF requests?

Answer 4

A VDF station can give True or Magnetic bearings.
* QDM: Magnetic bearing to the station.
* QDR: Magnetic bearing from the station.

Question 5

DF bearing classifications?

Answer 5

• Class A: Accurate within ±2°
• Class B: Accurate within ±5°
• Class C: Accurate within ±10°
• Class D: Accurate to less than class C.

Question 6

DF errors?

Answer 6

Synchronous transmissions cause multi-path errors, which can cause erroneous bearings.

Question 7

The line of sign formula?

Answer 7

Range = 1.23 x (sqrt(Tx_height) + sqrt(Rx_height))

Range(nm)
Height(ft)

Question 8

LoS limitations?

Answer 8

Curvature of earth.

Question 9

Adcock Antenna?

Answer 9

Used for VDF, looks at different phase and amplitude of arrivial signal to be able to direction find.

Question 10

QGH?

Answer 10

controller-interpreted DF let-down procedure, on UHF or VHF