Image frequency is defined as an undesired carrier frequency that differs from the frequency to which a super heterodyne receiver is tuned by twice the intermediate frequency. In a receiver system, usually a heterodyne system, two inputs are accepted by the mixer; one the signal to be detected and second the local oscillator, which is a super heterodyne, at frequencies fs and f0 respectively. The output frequency of the mixer is fif = fs±fo . The output passes through a filter whose bandwidth is denoted by Δ . Therefore, given the filter's bandwidth as Δ and oscillator's frequency fo , signals of frequency fs = fo±Δ can be detected by the receiver. Usually one needs only one band and the unwanted one is called as the image.
