Abstract: In a circuit arrangement of a control station in a radio communication system comprising a plurality of substations, such as a land mobile telephone system, a measuring circuit measures an intensity of electric field in an up control channel to the control station during each quiescent period of signals in the up channel to detect jamming waves. Each quiescent period preferably appears in the up control channel in response to selected control signals of a down control channel to the substations. On detection of the jamming waves, the control channel is switched to a preselected one of speech channels between the control station and substations by switching circuits to use the preselected speech channel as a new control channel.

Abstract: A malfunction detection system sends a test calling signal to the mobile base station receiver and receives a response signal from the mobile station transmitter. A controller in the malfunction detection system monitors the access channel for proper operation and transmits an alarm signal to the mobile station controller when a problem is detected.