A hop rate detector, for receiving frequency-hopped signals carrying information data, which generates a tone at the "hop rate" when modulated or unmodulated frequency-hopped signals are present. The input signal is channelized into sub-bands via filter banks and the signal in each channel is power detected (squared) and compared to a present threshold to produce a positive voltage (="1") if the threshold is exceeded and zero volts (="0") otherwise. The channel signals are split into an upper band (B.sub.u) and lower band (B.sub.d), then each band is summed and the lower band sum subtracted from the upper band sum to provide a first stage signal. The first stage signal has its DC component removed, then is multiplied by a delayed copy of itself to provide a frequency tone indicating the hop rate of the received signal.