A system for monitoring the electromagnetic field strength received at a predetermined point of a monitored area, includes a device that senses the electromagnetic field fed in at a least one frequency band to an antenna by a transmission apparatus and transmits at least one RF power signal indicative of electromagnetic field strength to a control center. With the control center a geographic data base is available that includes information items on the mutual position of the antenna and the predetermined point. A processing facility with the control center is configured for receiving the RF power signal from the device and calculating from the RF power signal and the data base items the field strength received at said predetermined point from the antenna.