Abstract: In this paper,experimental results are analysed for HF sweep-frequency backscatter and oblique transmission passing through the ionosphere.The quasi-real-time frequency prediction has been obtained by (P-f) ionogram.Frequency prediction table is given.Several important parameters of the ionosphere can be provided,such as LOF,MOF,MUF and effects of Es etc.The window of optimum operating frequency is given.Both backscatter and oblique ionogram,to be measured together,are discussed.This frequency prediction method can correct long or short term prediction,which is calculated by vertical sounding data,because the former was a quasi-real-time frequency prediction for a fixed communication line.