DF Accuracy Requirements for Monitoring Stations

Radio direction finders (DF) in spectrum monitoring are widely used to locate transmitters such as radio frequency (RF) interferers and unlicensed broadcasting stations. In fixed monitoring stations (FMS), two or more DFs are installed on masts and allow geolocation of transmitters via triangulation. In mobile monitoring stations (MMS), the DF is installed on a vehicle roof and allows geolocation of transmitters on the move via homing. In transportable monitoring stations (TMS), two or more DFs are temporarily installed at exposed sites and allow geolocation of transmitters via triangulation. Other methods for locating transmitters include time difference on arrival (TDOA) and power on arrival (POA).

In this document, we focus on triangulation since this method is used in the vast majority of use cases. Following international standards, DF accuracy refers to system DF accuracy, i.e. the average difference between the nominal direction of arrival and the DF result from the DF system connected to a DF antenna in a reflection-free environment. The system DF accuracy should not be confused with the instrument DF accuracy (DF accuracy of the DF processor without a DF antenna) or operational DF accuracy (DF accuracy of the installed DF system in the operational environment including reflections).