Which statement best describes the function of a preselector in a superheterodyne RF front end?

• A. It attenuates out-of-band signals before the mixer to reduce image interference and protect the mixer.
• B. It amplifies the aggregate signal after the mixer.
• C. It narrows the IF bandwidth to improve selectivity.
• D. It changes the LO frequency to tune channels.

Answer: (A)

In a superheterodyne RF front end, the preselector is a tunable RF filter that passes only the desired frequency range and attenuates signals outside it. By reducing strong out-of-band signals before they reach the mixer, it helps prevent mixer overload and intermodulation that can create image interference—signals that would fold into the same intermediate frequency as the desired signal. This improves the receiver’s protection of the mixer and overall selectivity. The other functions—amplifying the signal after the mixer, narrowing the IF bandwidth, or changing the LO frequency to tune channels—belong to other stages or mechanisms in the receiver.