Radio frequency energy signalling apparatus

In combination in radio frequency signal detecting apparatus for signalling the incidence of radio frequency energy of a predetermined spectrum exceeding a preselected adjustable threshold, an operational amplifier having inverting and noninverting input terminals and an output terminal, said operational amplifier including a difference amplifier having inverting and noninverting input terminals and an output terminal, said noninverting input terminal of said difference amplifier corresponding to said noninverting input terminal of said operational amplifier and said output terminal of said difference amplifier corresponding to said output terminal of said operational amplifier, a first resistor connected between the inverting input terminals of said operational amplifier and said difference amplifier and a second resistor connector between said inverting input and output terminals of said difference amplifier, a light emitting diode connecting to the output of said operational amplifier, and a coupling-detector network connected to the inverting and noninverting input terminals of said operational amplifier, said coupling-detector network including an input terminal, a third resistor and a potentiometer connecting said operational amplifier inverting input terminal to a fixed potential, means connecting the tap of said potentiometer to said operational amplifier noninverting input terminal, a capacitor connected in parallel with said third resistor and potentiometer, a detector diode connected between said coupling-detector network input terminal and the inverting input terminal of said operational amplifier, a potential source, and a fourth resistor connecting said potential source to the junction between said third resistor and said potentiometer.