A method for detecting a jamming transmitter affecting a communication user equipment, operating in a cellular network supporting communication in a time-division manner, including at least one active base station, on which the user equipment is camping. In the method, the user equipment detects that at least one downlink radio channel from the active base station is not decodable, measures signal levels received on said downlink radio channel for a plurality of time units, analyzes said signal level measurements, and in case at least one time unit is detected with a signal level exceeding a predefined threshold, detects a jamming transmitter by verifying that, in a predefined amount of successive time units, the pattern of a first time unit with signal level exceeding the predefined threshold, directly followed by a second time unit with a signal level below the predefined threshold, is not detected.