Modulated, current-driven, electrostatic ion-cyclotron (CDEIC) waves are shown to exhibit amplitude and frequency modulation, spectral broadening, and time-averaged frequency pulling. The observed spectral broadening is asymmetric and sensitively dependent on the driving frequency. Qualitative features of the experimental data are reproduced by the forced van der Pol equation and are explainable using processes associated with driven self oscillations. These results may be relevant to ionospheric modification experiments involving the controlled modulation of the natural electrojet. ¿ American Geophysical Union 1994