Image frequency in a superheterodyne receiver Which statement correctly describes the image frequency in a superheterodyne architecture with an intermediate frequency (IF)?

Introduction / Context:
In superheterodyne receivers, any RF signal that mixes with the local oscillator (LO) to produce the same IF as the desired signal is called the image. Image responses can degrade selectivity and cause interference if not handled properly in the RF front end.

Given Data / Assumptions:

• Receiver uses one RF preselector, a mixer, and an IF strip centered at a fixed IF (e.g., 455 kHz).
• LO may be above or below the desired signal (high-side or low-side injection).
• IF filters pass the IF band around the fixed IF frequency.

Concept / Approach:

The image frequency is separated from the desired RF by 2IF. After mixing, both the desired signal and the image convert to the same IF. Therefore, once inside the IF chain, the IF filters cannot distinguish between them. Image rejection must be achieved ahead of the mixer by the RF tuned circuits or preselector filters with adequate quality factor and appropriate tracking.

Step-by-Step Solution:

Verification / Alternative check:

Receiver textbooks show image-rejection ratio is largely set by the RF tuned circuits bandwidth relative to separation 2IF.

Why Other Options Are Wrong:

(a) Image depends on tuned frequency and IF; (b) it can fall inside the front-end tuning range; (c) image exists in AM, SSB, FM, etc.; (e) detectors operate at IF or baseband and do not perform image rejection.

Common Pitfalls:

Confusing image rejection with adjacent-channel selectivity; assuming IF filters alone solve image problems.

Final Answer:

It is not rejected by the IF tuned circuits