The document specifies a method for determining field strength which can be used in mobile radio systems, such as Bluetooth. The principle proposed involves alternate transmission and reception in the mobile radio system, with each timeslot comprising at least one time interval for transmitting/receiving a data block (RX, TX). The reception field strength (RSSI) is measured directly before (A, B) or directly after (C, D) transmission or reception of the data block (RX, TX). This allows the number of locking operations required in a PLL to be reduced and still allows adaptive channel adjustment to be performed, for example in a "frequency hopping method", by measuring all channels without reducing the net data rate.