Plain-language answer: Knife-edge diffraction is bending of a radio wave around a relatively sharp obstruction such as a ridge or roof edge.
Why it changes the path
It can permit a usable signal without direct clearance, but adds loss determined by geometry, wavelength, and the obstruction’s position in the path.
What to observe
Model the profile with accurate endpoint and obstacle heights, then confirm with field measurements.
The common mistake
Assuming a single visible ridge either blocks everything or costs a fixed number of decibels.
Planning boundary
Propagation models and field regions depend on frequency, geometry, terrain, atmosphere, polarization, antenna pattern, and measurement distance. Use them to plan and compare—not to guarantee a contact or installed range.
