A narrowband interference excision and nulling system for Global Positioning Satellite (GPS), spread spectrum navigation and communication bands, and an antijam electronic apparatus that operates using RF conversion and digital signal processing. A band containing the signal of interest as well as interference is converted to an intermediate frequency (IF) for RF filtering using single conversion, and this signal is digitized using an analog-to-digital converter (ADC). A representation of the signal is produced at a lower frequency using digitization and filtering, and a continuous data representation of the band is processed using multiple-point samples to define the input to a complex FFT. The FFT produces contiguous frequency bins that are examined to identify narrowband and broadband interference. An excision algorithm determines the optimum pattern of bins to be removed, after which the residual bins are reconstructed using an IFFT, followed by digital-to-analog conversion and RF conversion to the output band. Narrowband interference excision can be integrated with two-port broadband suppression in cascade using a masked variable resolution FFT spectral energy detection receiver.