 Most superheterodyne receivers use a variable-frequency oscillator, mixer, and filter to tune the desired signal to a common intermediate frequency or baseband, where it is then sampled by the analog-to-digital converter.However, in some applications it is not necessary to tune the signal to an intermediate frequency and the radio frequency signal is directly sampled by the analog-to-digital converter (after amplification).Real analog-to-digital converters lack the dynamic range to pick up sub-microvolt, nanowatt-power radio signals.