Prediction of diffraction effects due to irregular terrain on radio wave propagation in the VHF and UHF bands

Many models have been proposed to represent diffraction effects on the propagation of radio waves over irregular terrain in the VHF and UHF bands. Predictions from these models have been compared with results from associated field-strength measurements available in extensive databases that also incorporate the technical parameters of thousands of VHF and UHF links. Some possible sources of the still high values of the standard deviations of errors between predictions and measurements will be identified and discussed, with particular attention to uncertainties on digital elevation models and on the effective Earth´s radius, as well as to effects from lateral propagation.