When you call 911 from a cell phone on land, the dispatcher can usually determine your location in just a few seconds between your phone’s internal GPS and the location information available from the cellular network. However, this is not necessarily the case when a mariner transmits a distress call over a VHF marine radio. Instead, search and rescue authorities rely on radio direction-finding systems to locate mariners in distress — even when those individuals are unable to determine or communicate their position.

Radio direction finders calculate the direction of a radio transmitter by analyzing the signal as it reaches the antenna. A single direction finder can determine a line of bearing toward the transmitter; multiple direction finders can be used together to triangulate the location of the transmitter. From tracking EPIRBs, ELTs, PLBs, and other marine survivor locating devices to finding a distressed mariner unable to provide a latitude/longitude, radio direction finding technology has saved countless lives and is a vital tool for search and rescue.

Why do you need a radio direction finder? A radio direction finder can be a valuable safety tool, even for commercial and recreational vessels that do not typically engage in search and rescue operations. For example, a direction finder can be used to locate a man overboard by homing in on the signal from a crew member’s personal locator beacon, man overboard beacon, or even a handheld radio.