In a receiver front end, what is the chief purpose of adding a preselector stage ahead of the mixer? Choose the benefit most directly provided by the preselector.

Introduction / Context:
A preselector is a tunable band-pass filter placed before the mixer in a superheterodyne receiver. Its role is to admit the desired RF signal while rejecting out-of-band energy, including image frequencies and strong interferers that can overload or create spurious mixer products.

Given Data / Assumptions:

• Tunable RF front end with at least one resonant circuit.
• Mixer produces sum and difference products, sensitive to out-of-band signals.
• Image frequency is offset by 2×IF from the desired RF for a given LO injection.

Concept / Approach:

By sharpening the RF selectivity, the preselector reduces energy at the image and other undesired signals before they reach the nonlinear mixer. This improves dynamic range and reduces desensitization. While audio fidelity and PA linearity are important, they are not functions of the preselector.

Step-by-Step Solution:

Verification / Alternative check:

Receiver block diagrams show preselectors or RF band-pass filters explicitly specified for image rejection and front-end protection from strong adjacent signals.

Why Other Options Are Wrong:

• Audio fidelity: governed by IF/audio stages and demodulator, not the preselector.
• Power amplifier linearity: unrelated to RF input filtering.
• Wider passband: opposite of the preselector’s purpose.
• Eliminating AGC: AGC manages gain, not selectivity.

Common Pitfalls:

Assuming preselection is optional; in high-interference environments, it is essential to maintain sensitivity and prevent intermodulation.

Final Answer:

Provide higher selectivity and image/interference rejection before mixing