VDF

Question 1

VDF principle of operation?

Answer 1

The equipment consists of a directional antenna system and a VHF radio receiver which is able to determine the direction of VHF communication signals.

Question 2

Is VDF used by the pilot or a ground based operator?

Answer 2

Ground based operator

Question 3

An aircraft which requires a series of bearings or headings, should call the DF station on the appropriate frequency and request the service by the signal….?

Answer 3

QDL followed by other appropriate Q signals.

Question 4

VDF bearings class A should be accurate within?

Answer 4

Plus or minus 2 degrees

Question 5

Frequency range VDF:

Answer 5

118mhz to 136mhz

Question 6

Bearings are provided, by ?, on an aircraft’s ?

Answer 6

Bearings are provided, by voice, on an aircraft’s VHF Communications frequency

Question 7

The accuracy of the observation is classified as follows:
• Class A – Accurate within ± _°
• Class B – Accurate within ± _°
• Class C – Accurate within ± _°
• Class D – Accuracy less than Class C

Answer 7

The accuracy of the observation is classified as follows:
• Class A – Accurate within ± 2°
• Class B – Accurate within ± 5°
• Class C – Accurate within ± 10°
• Class D – Accuracy less than Class C

Question 8

The VDF display is located -

Answer 8

on the ground at ATC unit

Question 9

Factors Affecting Accuracy
• Propagation error and site error caused by the aircraft’s transmissions being reflected from
terrain as they travel to the site, or being reflected from buildings at the site.
• Aircraft attitude: the VDF System and VHF Communications are vertically polarized;
therefore, best reception and results will be obtained when the aircraft flies straight and
level.
• Poor accuracy is likely in the overhead of a VDF receiver, particularly with the latest Doppler
systems. The reception of both Direct Wave and Ground Reflected Wave can cause signal
fading or loss; the phenomenon is usually short-lived. Together with other multi path signals
this gives rise to bearing errors.
• Synchronous transmissions by two or more aircraft will cause momentary errors in bearings.

Answer 9

Factors Affecting Accuracy
• Propagation error and site error caused by the aircraft’s transmissions being reflected from
terrain as they travel to the site, or being reflected from buildings at the site.
• Aircraft attitude: the VDF System and VHF Communications are vertically polarized;
therefore, best reception and results will be obtained when the aircraft flies straight and
level.
• Poor accuracy is likely in the overhead of a VDF receiver, particularly with the latest Doppler
systems. The reception of both Direct Wave and Ground Reflected Wave can cause signal
fading or loss; the phenomenon is usually short-lived. Together with other multi path signals
this gives rise to bearing errors.
• Synchronous transmissions by two or more aircraft will cause momentary errors in bearings.