an improved aircraft marker beacon receiving and indicating system is provided , which automatically responds to the amplitude of the received signals to provide reduced sensitivity and muting of audio output after initial sensing and indication of proximity to the beacon and during a timed period of passing over the beacon in closest proximity thereto . the improved system employs an electrically controllable radio frequency attenuator between the antenna and the input of the receiver . the attenuator is controlled by a control voltage of predetermined duration from a trigger actuated , timed control signal generator . the control signal generator is triggered by direct current trigger pulse signals from an audio frequency peak detector . the peak detector derives its input from an operational amplifier coupled to receive audio frequency signals from the demodulator output of the tuner portion of the receiver . the control voltage from the timed control signal generator is applied to the reference input terminal of the operational amplifier to mute the loudspeaker or headphones coupled with the output of the operational amplifier , as well as to the attenuator to reduce the sensitivity of the receiver .