Editing Superheterodyne receiver (section)

===IF bandpass filter===
The IF stage includes a filter and/or multiple tuned circuits to achieve the desired [[selectivity (radio)|selectivity]]. This filtering must have a band pass equal to or less than the frequency spacing between adjacent broadcast channels. Ideally a filter would have a high attenuation to adjacent channels, but maintain a flat response across the desired signal spectrum in order to retain the quality of the received signal. This may be obtained using one or more dual tuned IF transformers, a quartz [[crystal filter]], or a multipole [[ceramic resonator|ceramic crystal filter]].<ref name="QSL"/>

In the case of television receivers, no other technique was able to produce the precise [[bandpass]] characteristic needed for [[vestigial sideband]] reception, such as that used in the [[NTSC]] system first approved by the US in 1941. By the 1980s, multi-component capacitor-inductor filters had been replaced with precision electromechanical [[surface acoustic wave]] (SAW) [[Electronic filter|filters]]. Fabricated by precision laser milling techniques, SAW filters are cheaper to produce, can be made to extremely close tolerances, and are very stable in operation.