Foliage Loss
Edit on GitHubHow trees and vegetation attenuate 433 MHz signals, with the numbers you can expect in forest, and what to do about it.
Foliage Loss
Trees are the quiet killer of UHF range. A beacon in a forest sounds weak not because it is broken but because every leaf is a small absorber and scatterer of radio waves.
The numbers
At 433 MHz, single-tree attenuation is modest, but the forest is not a single tree:
| Environment | Extra loss vs open field |
|---|---|
| Single tree in the path | 3 - 6 dB |
| Sparse woodland (10 - 20 m spacing) | 10 - 20 dB |
| Dense forest, summer | 20 - 30 dB |
| Dense forest, winter (bare) | 8 - 15 dB |
Summer foliage roughly doubles the loss of winter: leaves are mostly water, and water absorbs microwaves.
The physics
Each leaf scatters and absorbs a little signal. Over a path through many trees, the losses add. Because the loss is cumulative, the first 50 m of forest hurts more than the second 50 m of open field helps. Foliage also depolarizes the signal, which costs another few dB at the receiver.
What to do
- Get above the canopy: the fastest fix. A beacon on a ridge or a pole above the trees gains 15 - 25 dB over one at ground level.
- Shorten the path through the trees: follow game trails and clearings rather than a straight line.
- Move 20 m: a small lateral shift can change the foliage depth dramatically.
- Raise the receiver too; the same loss applies on the search side.
The honest expectation
In dense summer forest, plan for beacon range in hundreds of meters, not kilometers. This is not a defect; it is the physics of the environment. The Winter Operations page notes that winter recovers much of the loss.
Related pages
- Propagation and Range for the summary
- Antenna Height Matters for the height lever
- Line of Sight and Terrain for terrain interplay