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1. Abbr. for daylight factor.
2. On drawings, abbr. for drinking fountain.
DF (direction finder)
A radio receiver equipped with a direction-sensing antenna used to take bearings on a radio transmitter. A direction finder essentially consists of a loop aerial. To remove 180° ambiguity, a sense aerial is also brought into the circuit. The DF system can either be airborne or ground-based. See automatic direction finder.