Radio Shadow
Edit on GitHubThe dead zones where a beacon signal disappears, why they exist, and the systematic way to find and escape them.
Radio Shadow
Every terrain has places where the signal simply is not there: radio shadows. Understanding them is the difference between “the beacon is broken” and “the beacon is in a shadow”.
What creates a shadow
| Cause | Size of shadow |
|---|---|
| Ridge or hill in the direct path | Meters to kilometers |
| Deep valley floor | Hundreds of meters |
| Building canyon | Tens of meters |
| Ground depression (dip in terrain) | Tens of meters |
| Dense forest with wet canopy | Tens of meters |
The signature
A radio shadow has a tell: the signal drops sharply when you cross a boundary, then returns just as sharply a few meters later. If the RSSI is stable and then suddenly -20 dB at one specific spot, you have found a shadow boundary, not a fault.
Searching through shadows
- When the signal vanishes, move laterally 10 - 30 m, not forward.
- Climb: most shadows have a height ceiling where the path clears.
- Circle the shadow: the beacon is usually audible from its edges.
- Mark the boundary: shadows are consistent; the same spot will be dead tomorrow too.
The beacon side
A beacon cannot know it is in a shadow. That is why the deployment checklist requires a confirmation check: deploy, walk 100 m away, listen, and adjust position if the signal drops (Field Deployment).
Related pages
- Mountain Effects on Radio for the terrain version
- Search Patterns and Procedure for the systematic search
- Outdoor Testing for the confirmation check