automatic VHF/DF (very high frequency/direction finder)
A ground-based direction-finding system in which, instead of manually turning the DF aerial to find the null position, it is done automatically. The direction of the transmitting source is immediately indicated on the CRT (cathode-ray tube) console of the equipment. The system is essentially based on a loop aerial that finds the direction of the transmitter and a sense aerial to remove 180° ambiguity. See automatic direction finder.