Abstract: The present invention relates to a monitoring system for land-based navigational and landing systems. A monitoring system of this type monitors the functions that are carried out by the navigational and landing system, especially the information that is transmitted to the aircraft. According to the present invention, external interfering influences that are independent of the system are detected and are taken into account in the monitoring.

Abstract: The invention deals with a surveillance system for terrestrial navigational and landing systems, in which the navigational signals being transmitted for aeroplanes or other airborne objects by the navigational and airport landing systems are received and evaluated by a ground-based receiving and control facility. In this system: the receiving and control facility is equipped with a plurality of additional receiving stations; these additional receiving stations operate in the frequency range of the navigational signals; the additional receiving stations are arranged geographically distributed within the transmitting range of the navigational or airport landing system; the signals recorded by the additional receiving stations are forwarded to a central evaluating unit.

Abstract: A mobile-radio system is disclosed in which it is possible to selectively monitor and interfere with calls. To this end, the base station includes an intercept device (5) whereby at least one traffic channel is can be intercepted, i.e., whereby transmissions on this channel can be intercepted or jammed. The intercept device (5) is connected to a baseband-processing portion (1).