OVERVIEW: Generic HF/DF (High-Frequency Direction Finding), also known as "Huff-Duff," is a passive radio frequency system used to detect and determine the direction of high-frequency (HF) radio transmissions. It plays a critical role in electronic support measures (ESM), signals intelligence (SIGINT), and maritime situational awareness.

GENERAL DESCRIPTION: HF/DF systems operate by detecting high-frequency (3–30 MHz) radio signals and measuring their direction using rotating antennas or phased arrays. Primarily used for locating enemy transmissions, navigation aids, and search and rescue operations, HF/DF provides bearings to signal sources over long distances due to HF wave propagation characteristics. Commonly installed on naval vessels, aircraft, and ground stations, these systems enhance situational awareness and signal intelligence collection.

ROLE SUMMARY:
Category: Electronic Support Measures (ESM) / Direction Finding
Primary Use: Locating HF radio emitters for navigation and intelligence
Function: Passive detection and bearing measurement of HF signals
Platform: Ships, aircraft, land-based stations
Integration: Works with COMINT and command systems for tactical cueing

See Specific information under [Sensors/EW] section.

SOURCE:
Naval Electronic Warfare Manuals
https://en.wikipedia.org/wiki/High-frequency_direction_finding