Signal Strength Mapping

RSSI numbers become useful when they become a map. This page is the practice of walking a route with a receiver and building a signal map of the area.

The method

1. Put a receiver (second beacon in RX, or SDR) on the beacon’s channel.
2. Walk a grid or a route, stopping at marked points.
3. Record RSSI and position at each stop.
4. Mark the map: strong, medium, weak, nothing.

Reading the result

The map reveals the area’s radio personality:

Pattern	Meaning
Smooth gradient	Open terrain, no obstacles
Sharp cliffs of signal	Ridge and shadow boundaries (see Radio Shadow)
Patchy alternation	Multipath from buildings or rock faces (see Propagation Modes)
Dead hollows	Valley traps (see Mountain Effects on Radio)

The contours

Every -6 dB marks half the power; on the map this looks like a contour line. Drawing the contours by hand at -80 and -100 dBm gives the usable coverage area at a glance: the searchable region for that beacon placement.

Using the map

• Before the trip: choose the deployment point whose coverage circle covers the intended area (see Field Deployment).
• During a search: walk the strong edges first; the beacon is probably near the coverage boundary.
• After a failed reception: the map shows whether the problem is placement or hardware.

Related pages

• RSSI Explained for the numbers
• Radio Shadow for the dead zones
• Outdoor Testing for the procedure