A self-calibrating modulator apparatus includes a modulator having a controlled oscillator and an oscillator gain calibration circuit. The oscillator gain calibration circuit includes an oscillator gain coefficient calculator configured to calculate a plurality of frequency dependent oscillator gain coefficients from results of measurements taken at the output of the controlled oscillator in response to a test pattern signal representing a plurality of different reference frequencies. The plurality of frequency dependent gain coefficients determined from the calibration process are stored in a look up table (LUT), where they are made available after the calibration process ends to scale a modulation signal applied to the modulator. By scaling the modulation signal prior to it being applied to the control input of the controlled oscillator, the nonlinear response of the controlled oscillator is countered and the modulation accuracy of the modulator is thereby improved.