A signal detector for detecting a signal having a first nominal frequency, F1 and a second nominal frequency F2, the signal intermixed with an interfering signal to form a composite signal, the signal detector including a first and a second band pass filter centered at F1 and F2 for filtering the composite signal to provide an F1 and F2 signal; a parameter estimator for determining an F1 and F2 period for the F1 and F2 signal for a sequence of frames and an average period shift (APS) for a current frame and a plurality of earlier frames; a metric calculator for calculating a metric that corresponds to the F1 and F2 period and the APS; and a decision processor for deciding whether the signal has been detected based in part on a comparison of the metric and a threshold.