speaker 28 providing an audible warning refer now to fig3 for a detailed description of noise riding threshold circuit 34 all noise riding threshold circuits 34a j of fig2 operate in the same manner all components described in fig3 use only numerals these components are identical to the ones in fig1 and 2 that have the same numerals and an identifying letter the noise compensator 32 and the comparator 30 within the noise riding threshold circuit 34 receive an input signal 35 from video amplifier 18 the input signal 35 is comprised of noise components 37 and the radar emission pulse 39 the radar emission pulse 39 only appears for a short period of time in a complete cycle obviously if there is no received pulse at antenna 10 of fig2 only the noise components 37 will be present the noise components 37 appear throughout the cycle in the present invention the dc level of the video amplifier 18 output is about 1 5 volt within noise compensator 32 an operational amplifier 40 receives the input signal 35 from video amplifier 18 through a dc blocking capacitor 42 and a load resistor 44 resistor 44 establishes the dc input level at 0 volts operational amplifier 40 has connected to it a resistor 46 and a.