Results obtained on experimental radio circuits over medium distances

Measurements of the strength of hf signals received after propagating through the ionosphere over paths of medium length (160 and 790 km) in temperature latitudes during a period of high solar activity (R sub 12 = 130 to 150) give experimental monthly medians for the hourly propagation losses. A systematic comparison between these values and those calculated on the basis of currently used propagation models is carried out. The order of magnitude and morphology of the deviations are interpreted partly in terms of ionospheric absorption and partly in terms of magneto-ionic modes and polarization effects.