Abstract: Circuitry and methods are presented for detecting the presence of a spectrally distributed signal having a known distribution, e.g. spread spectrum, in a strong noise environment. The signal is split into two channels, each filtering a predetermined frequency band within the given spectrum. The channels are tuned and balanced so that they pass differential amounts of signal energy that may be present but provide equalized noise outputs. The channels are alternately coupled to the input of an energy detector which provides a DC component responsive to the difference in the signal levels of interest, while effectively cancelling noise energy components in each channel. In the spread spectrum example the frequency bands are typically selected to the maximum and a null location in a ##EQU1## distribution.