V.H.F. transmission over distances of 140 and 300 km

A description is given of measured field-strength characteristics on 186 and 174Mc/s over distances of 140 and 300km, respectively. The fading characteristics on the shorter path are consistent with the assumption that three propagation modes can be detected: a ground wave, a wave reflected at an elevated layer and a scattered component. The cumulative field-strength distribution can be interpreted in terms of the distribution of the mode components. On the longer path, the optimum layer height, corresponding to the greatest signals, is about half that of the intersection point of horizon rays on a 4/3-earth profile. No significant correlation was observed on either path between surface refractive index and monthly median field strength.