A quadrature demodulator receiver unit (100) comprises a first filter unit (360) that may delay an intermediate signal x(t) whose real part is based on a sampled in-phase IF signal (xi(t)) and whose imaginary part is based on a sampled quadrature IF signal (xq(t)). A second filter unit (366) filters a conjugate complex version of the intermediate signal x(t). The filter coefficients of the filter units (360, 366) are determined using a calibration signal, for example on the basis of ratios of complex-valued spectral components of intermediate signals xcal(t) obtained from the calibration signal cal(t). The filtered signal and the delayed signal are recombined to obtain a compensated output signal y(t). The calibration signal may be supplied from an oscillator circuit supplying a signal for processing a receive signal of the receiver unit (100).