Results of investigating the spatial and temporal HF field structure near the skip distance are presented. The data were obtained on midlatitude radio paths less than 1000 km in length, using broadcasting stations as sources of the probe signals. The signals reflected by the ionosphere were received and processed with a multichannel coherent receiver and the largest phased array of the decameter radio telescope UTR-2. The strong dependence of the probe signal parameters on the ionospheric plasma conditions has allowed formulating and solving a number of model inverse problems of ionospheric diagnostics. It proves possible to determine parameters of the parabolic ionospheric layer, and the effective electron collision frequency, to evaluate horizontal gradients of the electron density and some parameters of the medium-scale-size ionospheric irregularities. A number of tests made both within the method and by means of comparison of the restored parameters against the data of other diagnostic techniques demonstrate the high potential and accuracy of the approach described in the paper. ¿ American Geophysical Union 1996