VDF is also called Homer.
It operates in the VHF band of 118-136 MHz.
It assists a/c to home onto a requested bearing or a landmark.
The a/c does not require any special equipment except the Standard VHF Radio Telephony set.
Ground equipment requires-
- VHF radio Telephony set
- Lop and Sense Aerial
- Radar Display Unit
The a/c is required to transmit on the VHF Radio Telephony set so that his a/c is visible as a blinking light on the Ground Radar Unit that remains on for the entire period the a/c is transmitting on its VHF Radio Telephony set.
The VHF Radio Telephony set located on the ground receives the transmission and identifies the a/c on their Radar screen, with reference to bearing from the station.
Sometimes an a/c can ask for the bearings from the ground station by Transmitting on the VHF Frequency.
When a series of bearings are requested to locate the a/c position or to generate a FIX of the a/c, the a/c uses word QDL that means request series of bearings in his Transmission followed by the test call, which usually comprises three different bearing.
The waves in Very High Frequency travels as line of sight waves, therefore the range depends mainly on the height of the Transmitter and the Receiver.
The Formulae for calculating the same is as follows-
1.25 √Height of A/c + 1.25 √Height of Transmitter
Similarly the range for Super High Frequency, whose wave also travels as line of sight waves, the range again depends on the height of the Transmitter and the Receiver.
The range for the same can be calculated by the formulae-
1.20 √Height of A/c + 1.20 √Height of Transmitter