A radio frequency signal level is determined by generating an AC reference voltage from a DC reference voltage and determining an envelope of the AC reference voltage in an envelope detector having substantially the same composition as an envelope detector for determining the envelope of the radio frequency signal. The AC reference voltage substantially eliminates any DC offset and thus induces a high immunity against temperature and power supply variations. Moreover, using substantially the same RF signal path for the RF signal and the reference signal, signal distortions cause by the RF signal path are substantially compensated for.