Page "Superheterodyne receiver" Paragraph 30

Usually the intermediate frequency is lower than the reception frequency f < small >< sub > d </ sub ></ small >, but in some modern receivers ( e. g. scanners and spectrum analyzers ) it is more convenient to first convert an entire band to a much higher intermediate frequency ; this eliminates the problem of image rejection.

Then a tunable local oscillator and mixer converts that signal to a second much lower intermediate frequency where the selectivity of the receiver is accomplished.

In order to avoid interference to receivers, licensing authorities will avoid assigning common IF frequencies to transmitting stations.

Standard intermediate frequencies used are 455 kHz for medium-wave AM radio, 10. 7 MHz for broadcast FM receivers, 38. 9 MHz ( Europe ) or 45 MHz ( US ) for television, and 70 MHz for satellite and terrestrial microwave equipment.