Abstract :
The obstacle gains are numerically illustrated as functions of the distance between the obstacle and the path terminal for the typical examples of a ridge, a bluff on a homogeneous earth and a cliff at a coastline. As the distance increases, these obstacle gains tend to become constants (i.e. the ridge gain, the bluff gain and the cliff gain that have been previously obtained), while, at short distances, they are directly affected by a diffraction loss, interference between the direct and reflected waves and other effects which are not optical in character. A convenient formula for the obstacle gain is introduced for the poor convergence of the relevant residue series. The obstacle gain defined here can be understood to be the gain caused by the earth´s inhomogeneity and also the gain caused by the antenna height, or it can be the `terminal gain¿, in the sense that the inhomogeneity in the vicinity of the path terminal is particularly emphasised by the effect of the antenna height. It can be used in the same way as the ordinary antenna-height gain over a homogeneous earth.
