spike modulation interference frequencies detection of these modulation frequency components causes activation of means for preventing the sea spike contaminated return signal from being further processed background of the invention application_number US 58150275 A description a radar signal video input terminal 20 is connected to a first delay means 22 which has its output connected to a second delay means 24 the output of second delay means 24 is in turn coupled to the input of an electronic switch or gate 26 whose output in turn is coupled to the input of a second gate 28 the output of gate 28 is coupled to the input of a gate 30 whose output terminal 32 forms the output terminal of the system a first subtractor device 40 has a first input terminal connected to the input to delay means 22 and a second input terminal connected to the output of delay means 22 the output of subtractor 40 is coupled to a control terminal 41 of gate 28 a second subtractor 42 has a first input terminal coupled to the input of delay device 24 and a second input terminal coupled to the output of delay device 24 the output of subtractor 42 is connected to a control terminal 43 of gate 26 a third subtractor device 44 has one input terminal coupled to the input of first delay device 22 and a second input terminal coupled to the output of second delay device 24 the output of subtractor 44 is connected to a control terminal 45 of gate 30 in operation radar.