Page "Superheterodyne receiver" Paragraph 24

mixer may inadvertently produce additional frequencies such as 3rd-and higher-order intermodulation products.

The undesired signals are removed by the IF bandpass filter, leaving only the desired offset IF signal at f < small >< sub > IF </ sub ></ small > which contains the original modulation ( transmitted information ) as the received radio signal had at f < small >< sub > d </ sub ></ small >.