The preselector is an additional resonant circuit located between the first RF amplifier stage and the first mixer stage in shortwave receivers.
Due to the additional tuned circuit of the preselector, only a small fraction of the frequency band is fed on to the mixer; this measure improves performance in the vicinity of strong signals, mirror frequencies are rejected.
A preselector can be connected to a shortwave receiver with a broadband front end as a separate unit, or it can be integrated into the receiver. This circuit, which is in itself inexpensive, can improve very much the large-signal stability, but an additional operating step is required and that makes the operation of a world band receiver more difficult for non-professionals, since the rpeselector must be retuned to maximum every time the frequency is changed. In addition, an incorrectly tuned preselector can simulate a defect, since no signal „gets through“ if the preselector tuning is incorrect.
High-quality (semi-)professional shortwave receivers in some cases have a preselector that can be switched off to simplify operation in the absence of strong signals in the band. In many high end receivers another form of preselection is used, so many sets use automatically switched band filters or have a mechanically (for example in the Collins R-390A or electronically (in the Grundig Satellit 650) tuned preselector circuit.