A passive entry and/or passive go system and am associated operating method is provided. According to an embodiment of the invention, the following steps are performed in an electronic key of the passive entry and/or passive go system: generation of a reference input value, supplying the antenna circuit with the reference input value, measurement of the characteristic parameters, while the antenna circuit is supplied with the reference input value, storage of the characteristic parameters, measurement of a first output value of the antenna circuit, and determination of the field strength from the first output value and the characteristic parameters, whereby an effect of the characteristic parameters on the field strength is compensated. Use, for example, in motor vehicles.