The upper-frequency cutoffs of magnetospherically reflected (MR) whistlers observed by the Ogo 1 and 3 satellites are explained in terms of trapping of the upper-frequency components above the cutoff by sharp density gradients across L shells. The lower-frequency cutoffs are interpreted in terms of waveguide attenuation and D region absorption of the atmospheric source energy and defocusing of the MR whistler energy in the magnetosphere.