1. A system for detecting the presence of a narrowband signal having a bandwidth ΔF2 in a wideband frequency channel having a bandwidth ΔF1>ΔF2, the system comprising: a receiver front-end section adapted to receive a received signal in a selected frequency channel having a bandwidth ΔF1, to digitize the received signal, and to output a digitized signal; a time domain to frequency domain transformer adapted to transform the digitized signal output by the receiver front-end section into N digital frequency domain components spanning the frequency channel; a spectral averager adapted to average the power spectrum of the N digital frequency domain components over a plurality of samples, K; a filter adapted to filter the averaged power spectrum of the N digital frequency domain components with a filter having M non-zero values spanning a bandwidth, ΔF3, where N>M and ΔF1>ΔF3; a statistics calculator computing a mean, μ k , a modified standard deviation, β k , and a peak value, P MAX of the filtered, averaged power spectrum of the N digital frequency domain components; and a detector adapted to detect the presence in the frequency channel of a narrowband signal having a bandwidth ΔF2 whenever P MAX >(k 1 *μ k )+(k 2 *β k ), where k 1 and k 2 are selected to provide a probability of detection, a probability of missed detection, and a probability of false alarm.