A receiver for analyzing input RF signals includes a first stage that includes an input for receiving one or more RF signals for analysis and a first local oscillator having an output including a first plurality of frequencies. The input is mixed with the local oscillator output in a first mixer to generate a first intermediate frequency spectrum output. A second stage includes a second local oscillator adapted to produce as output a sweep signal traversing a second plurality of frequencies and a second mixer for combining the second local oscillator output with the first intermediate frequency output to generate a second intermediate frequency output.