[en] Analytical relations are obtained which describe the modulation of an extraordinary wave propagating through a plasma with density pulsations across an external magnetic field. The modulation coefficients of the ordinary and the extraordinary waves are compared. The paper describes the results of experimental investigations carried out with the plasma of a reflecting discharge in the millimetre range of waves with the different polarization relative to the external magnetic field, which corresponds to ωsubH = (0.1 - 0.9)ω. The applicability of the modulation measurements of SHF oscillations for plasma diagnostics is discussed