High-frequency direction finding

Common card · No. 351183

High-frequency direction finding, usually known by its abbreviation HF/DF or nickname huff-duff, is a type of radio direction finder (RDF) introduced in World War II. High frequency (HF) refers to a radio band that can effectively communicate over long distances; for example, between U-boats and their land-based headquarters. HF/DF was primarily used to catch enemy radios while they transmitted, although it was also used to locate friendly aircraft as a navigation aid. The basic technique remains in use as one of the fundamental disciplines of signals intelligence, although typically incorporated into a larger suite of radio systems and radars instead of being a stand-alone system. In earlier RDF systems, the operator mechanically rotated a loop antenna or solenoid and listened for peaks or nulls in the signal to determine the bearing to the transmitter. This took considerable time, on the order of a minute or more. Radio operators could avoid being located by keeping their messages short...

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