The present invention relates to an adjustable circuit for filtering a transmission channel of an RFID signal and for suppressing a carrier signal in the reception path between an input gate and an output gate, including at least one adjustable oscillator for generating an oscillator signal, at least one input mixing stage cooperating with the oscillator for mixing an input signal by means of the oscillator signal to an intermediate frequency and a blocking device arranged downstream of the input mixing stage or the input mixing stages for suppressing the carrier signal at the intermediate frequency.