Image frequency

Image frequency: In radio reception using heterodyning in the tuning process, an undesired input frequency that is capable of producing the same intermediate frequency (IF) that the desired input frequency produces.

In a heterodyne receiver system, the mixer accepts two inputs, the signal to be detected and the local oscillator, at frequencies $f\_\{s\}$and $f\_\{o\}$, respectively. The frequency of the mixer's output is $f\_\{if\}\; =\; f\_\{o\}\; pm\; f\_\{s\}$The output is then passed through a filter, which inherently has a bandwidth (or uncertainty) denoted as $Delta$. Therefore, given an oscillator's frequency $f\_\{o\}$ and the filter's bandwidth $Delta$, the receiver can detect signals of frequencies $f\_\{s\}\; =\; f\_\{o\}\; pm\; Delta$. Typically, one wants only one band, and the other, unwanted band is called the image.The term "image" arises from the mirror-like symmetry of the detectable signal frequencies about the beating-oscillator frequency. Alternative name: mirror frequency ( [http://www.freepatentsonline.com/7227912.html] ).