Discussion
Why does a superheterodyne receiver need a preselector at all, given the intermediate frequency filter?
Answer: B
The image mixes to the same intermediate frequency as the wanted signal, so no filter after the mixer can separate them and the rejection must happen before. Impedance matching is a secondary benefit of the input circuit. Oscillator isolation matters but is not the preselector's purpose. And audio overload is prevented by gain control. This is the same reasoning as anti-alias filtering, and it recurs wherever an operation is irreversible.
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