A radar detector including a local oscillator capable of sweeping over a frequency range of sufficient bandwidth to provide a fundamental frequency and, when injected into a multiplier/mixer, harmonics of that fundamental frequency suitable for heterodyning with rf-signals received by an antenna. The heterodyning of the received rf-signals and the local oscillator signal produce an intermediate frequency signal of constant frequency. A sweep controller causes the local oscillator to sweep only through those local oscillator frequencies suitable for heterodyning with those received rf-signals having radio-frequencies which are of interest. The sweep controller causes the sweeping local oscillator not to sweep through those local oscillator frequencies which would heterodyne with received rf-signals that are not of interest.