A device and a method for determining a reference level for automatic gain control of a radio frequency signal to be received, particularly having a varying strength, in which method frames of a logical general packet control channel are received, as well as frames which have been transmitted with a predetermined transmission power level and by using a predetermined way of controlling the transmission power level. In the invention, said reference level is determined on the basis of at least one frame of a received radio block, or on the basis of at least one preceding frame, or on the basis of both of these, wherein the reference level is corrected on the basis of the signal strength measured during their reception.