Operational distinction: Reported coordinates are the starting point. Final location depends on the live beacon signal, field conditions and trained confirmation.
The field team begins with authorized alert information
The responding team does not independently obtain the beacon owner’s registration record. Available identity, coordinates and incident information are supplied through the responsible rescue authority and the organization managing the response.
Coordinates may be entered into agency-selected mapping software before deployment. Mapping can display the reported position, routes, assignments, terrain, team tracks and clues. It does not replace radio direction finding and does not prove that the beacon remains at the displayed point.
Responders are locating the beacon
Unless safety requires movement, a person who activates a distress beacon should remain with it, keep it operating and maintain the orientation and clear view of the sky specified by its manufacturer. If the person and beacon separate, responders may locate the beacon without locating the person.
406 MHz and 121.5 MHz perform different jobs
The 406 MHz transmission carries the coded distress message used by the satellite alerting system. It is a brief burst repeated approximately every 50 seconds, not a continuous signal. The lower-power 121.5 MHz transmission is intended for close-range homing by responding assets.
Detection range depends on terrain, antenna height, beacon installation and orientation, obstructions, receiver sensitivity and other field conditions.
Direction finding uses relative signal information
A directional receiver compares signal strength as its antenna is aimed in different directions. The operator looks for a repeatable increase rather than relying on one isolated reading. Guardian provides both numerical and audio signal-strength information for 121.5 MHz homing.
Reflections can produce misleading indications around metal buildings, vehicles, rock faces, terrain and other structures. Teams may take bearings from different locations, change antenna polarization, reduce receiver sensitivity near the source or use other approved techniques to separate the direct signal from reflections.
A bearing is not a target coordinate
A direction-finding observation consists of an observer position and a bearing toward the strongest repeatable signal. It establishes a line of bearing—not the distance to the transmitter.
A useful observation record may include:
- Team or operator identifier
- Observer latitude and longitude
- Bearing and whether it references true or magnetic north
- Frequency and time
- Relative signal strength or confidence
- Relevant field notes
Bearings from separated locations can help estimate a probable source area. Reflections, compass error, position error and poor geometry can prevent plotted lines from intersecting at the actual beacon. Any intersection remains an operational estimate until independently confirmed.
Close-in homing and source confirmation
As signal strength increases, teams may reduce sensitivity, repeat observations and approach from a different direction to confirm the indication. A transmitting beacon may be inside an aircraft, vessel, hangar, vehicle, building or terrain feature. The responsible agency confirms the source and resolves the incident under its procedures.
From alert to final location
- Cospas-Sarsat detects and routes the 406 MHz alert.
- The responsible authority supplies available alert and location information.
- The responding organization plans and deploys using approved systems.
- Field equipment detects or follows live beacon transmissions according to its capabilities.
- Direction-finding observations and close-range homing help locate the source.
- The responsible agency confirms and resolves the incident.
First read what happens when a beacon activates. Then compare current beacon-location tool categories.