The decision you should be able to make
Choose between detailed modelling, more height, a different route or a different band.
Core engineering
The single knife-edge model is an idealisation. ITU-R P.526 provides separate treatment for spherical Earth, isolated sharp or rounded obstacles, multiple obstacles and general terrain paths.
Obstacle shape matters: a broad rounded ridge is not equivalent to a thin roof edge, and a tree line is neither.
A link can show adequate received power during commissioning yet remain fragile if diffraction, multipath or vegetation has consumed the budget.
For an ideal knife edge, the dimensionless Fresnel-Kirchhoff parameter v combines obstacle height, wavelength and the two sub-path distances; ITU-R P.526 then maps v to additional loss.
Equipment and field checks
- Use software that states the diffraction model and permits inspection of the governing obstacle.
- Do not hide modelled diffraction inside an unexplained miscellaneous-loss entry.
- Where the prediction depends on obstacle shape, collect a higher-resolution profile or field measurements.
Do not progress until
The selected model matches the terrain geometry closely enough for the decision, and model uncertainty is reserved in the budget.
Limits and cautions
- Screening models support comparison; field validation is still required.
Primary sources
Sources were checked for this technical review. Recheck regulator and equipment requirements at the point of design or installation.