A communication device according to the present invention detects a frequency-hopped signal in an environment including sinusoidal interference. The frequency-hopped signal includes a frequency shift keying (FSK) sequence, where the sequence alternates between frequencies shifted from the carrier signal or hop frequency by positive and negative frequency offsets. The communication device of the present invention uses independent detection paths for each of the shifted frequencies. In the detection path for the upper frequency (e.g., positive frequency shift), a series of filters suppresses signals in the lower frequency band (e.g., negative frequency shift), while the detection path for the lower frequency employs a separate series of filters to suppress signals in the upper frequency band. The filter outputs from each detection path are separately examined to detect the presence of an expected signal.