Method of extracting field strength information, whereby an input voltage for an operational amplifier is generated from a signal via an input resistance provided in the form of a voltage divider circuit, and in order to change the input voltage at the voltage divider circuit, which comprises a plurality of divider nodes (RK0, RK1, TK1, RKM, TKN-1, RKN-1) and has a constant resistance value, a divider node (RK0, RK1, TK1, RKM, TKN-1, RKN-1) is selected and a partial voltage is tapped, and • an output voltage (UOUT) is generated by the operational amplifier by means of a fixed amplification factor, and • a control signal for selecting the divider nodes (RK0, RK1, TK1, RKM, TKN-1, RKN-1) is supplied by a control element connected to the output of the operational amplifier, and the control element has an input for the output voltage (UOUT), and • by selecting the divider nodes (RK0, RK1, TK1, RKM, TKN-1, RKN-1), the input voltage is changed until the output voltage (UOUT) lies within a predefined interval, and • the input voltage is tapped at the voltage divider circuit, characterised in that a receiver unit for receiving the electromagnetic signal is provided and the received signal is applied to a first terminal of the voltage divider circuit as an input signal, and • by means of the control element, which has an input for a reference voltage (UREF) for changing the input voltage by means of the control signal depending on a comparison of the output voltage (UOUT) with the reference voltage (UREF), a divider node (RK0, RK1, TK1, RKM, TKN-1, RKN-1) is selected so that the reference voltage (UREF) lies within the interval, and • a signal assigned to the control signal is supplied at an output of the control element, and the value of the assigned signal depends on the received field strength, and • a predefined value of a first variable is assigned to every divider node, and • the field strength value received by the receiver unit is determined by means of a comparison of the value of the first variable assigned to the selected divider node (RK0, RK1, TK1, RKM, TKN-1, RKN-1) with a field strength value assigned to the value of the first variable in a table of values. • an output voltage (UOUT) is generated by the operational amplifier by means of a fixed amplification factor, and • a control signal for selecting the divider nodes (RK0, RK1, TK1, RKM, TKN-1, RKN-1) is supplied by a control element connected to the output of the operational amplifier, and the control element has an input for the output voltage (UOUT), and • by selecting the divider nodes (RK0, RK1, TK1, RKM, TKN-1, RKN-1), the input voltage is changed until the output voltage (UOUT) lies within a predefined interval, and • the input voltage is tapped at the voltage divider circuit, characterised in that a receiver unit for receiving the electromagnetic signal is provided and the received signal is applied to a first terminal of the voltage divider circuit as an input signal, and • by means of the control element, which has an input for a reference voltage (UREF) for changing the input voltage by means of the control signal depending on a comparison of the output voltage (UOUT) with the reference voltage (UREF), a divider node (RK0, RK1, TK1, RKM, TKN-1, RKN-1) is selected so that the reference voltage (UREF) lies within the interval, and • a signal assigned to the control signal is supplied at an output of the control element, and the value of the assigned signal depends on the received field strength, and • a predefined value of a first variable is assigned to every divider node, and • the field strength value received by the receiver unit is determined by means of a comparison of the value of the first variable assigned to the selected divider node (RK0, RK1, TK1, RKM, TKN-1, RKN-1) with a field strength value assigned to the value of the first variable in a table of values.