Abstract: Apparatus for providing a direct quantitative readout of the amplitudes of arious frequency lines that constitute the envelope of an amplitude-modulated broadband noise signal. A selected band of carrier frequencies is fed to an AGC circuit that provides a constant-input signal amplitude to a demodulator for a period of time that is greater than the period of the lowest frequency of the modulating signal for detection. The detected signal is fed to a spectrum analyzer for the direct reading of the percent modulation.

Abstract: A method and means for passively detecting presence of noise radiating dees in a noise environment by determining the number of times per time sample that a received noise signal upwardly crosses a preselected threshold level, comparing this number with the number of upward crossings caused by a standard noise signal or background noise signal, and applying a predetermined ratio criteria. The noise sensors in the detection system may comprise a directional acoustic transducer in combination with an omnidirectional acoustic transducer, and acoustic transducer in combination with an artificially generated noise signal, or a single acoustic transducer.