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 radio blocks are received on a logical general packet data traffic channel of a signal, which radio blocks 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 continuously determined on the basis of correctly received or valid radio blocks, wherein the reference level is corrected on the basis of the signal strength measured during the reception of each valid radio block.