A tuner includes an analog block, a digital block, and an analog/digital conversion stage connected therebetween. The analog block includes a first attenuator/controlled-gain amplifier stage connected upstream to a frequency transposition stage. The overall mean power of the entire signal received by the tuner is calculated during a phase of initialization. This overall calculated power is compared in the digital block with a first predetermined reference value corresponding to a maximum power desired at a predetermined location of the analog block. The gain of the first attenuator/amplifier stage is adjusted to minimize the deviation between the overall calculated power and the reference value. In a phase of normal operation, one of the channels of the signal received is selected, with the gain of the first attenuator/amplifier stage being fixed.