AbstractThe proposed procedure and the corresponding circuits for the recognition of a frequency from a set of possible input frequencies in the frame of a time‐window interval seem to be advantageous as they lead to simpler hardware than the well‐known energy detector. A unique feature is the single channel processing possibility. In addition the decision on the presence or absence of a given frequency is much faster than with a filter bank of resonators in a nearly lossless resonators. the frequency response is however not monotonic in frequency but has a somewhat periodic shape. the cases of the real lossy or unstable circuits are also dealt with. Some aspects of circuit realizations are given.