RF Field Guide ยท reviewed reference
Trees and other obstructions
A visually clear path can still be a poor RF path when vegetation, buildings, terrain, or seasonal change intrude into the propagation volume.
Question
Why is line of sight not enough?
Inputs
- Terrain profile and endpoint heights
- Fresnel-zone clearance, vegetation type, seasonal state, and construction risk
Answer
Working
The first Fresnel-zone radius grows away from the endpoints and is largest near the middle of a symmetric path. Obstruction loss through foliage is variable with frequency, moisture, density, and geometry; it should be treated as a measured or explicitly modeled uncertainty, not a fixed universal dB value.
Visual explanation
- Terrain
- Structures
- Foliage
- Fresnel volume
- Seasonal growth
- Build margin
Interpretation
Survey the path at the critical clearance points. Account for tree growth, leaf-on conditions, planned buildings, and the fact that a profile's terrain surface may not include every obstruction.