Diurnal variation in a long distance VHF tropospheric path in the Brazilian Amazon region

This paper deals with an experimental study carried out in a long distance VHF tropospheric path located in the Brazilian Amazon region. Measurements of the received power in this path were registered for 170 hours and clearly indicate a diurnal variation characterized by the existence of two propagation mechanisms. Scatter propagation during the day and diffraction propagation in night hours. This information, together with the knowledge of the median values of the earth k-factor derived from these measurements are important input data for planning VHF and possibly UHF radio systems in low latitude areas.