Which statement best describes image frequency concept?

• A. The image frequency is the frequency that, when mixed with the LO, yields the same IF as the desired RF, potentially causing interference if not filtered.
• B. The image frequency is the LO frequency.
• C. The image frequency is the carrier frequency of the desired signal.
• D. The image frequency is the IF frequency.

Answer: (A)

In a superheterodyne receiver, the mixer combines the incoming RF with the local oscillator to produce a fixed intermediate frequency. Because the IF comes from the difference (or sum) of two frequencies, two different RF signals can end up producing the same IF. The image frequency is the RF frequency on the opposite side of the LO that, when mixed with the LO, yields the same IF as the desired signal. If the front-end filter doesn’t reject this image, it can cause interference and degrade reception. So the best description is that the image frequency is the RF frequency that, when mixed with the LO, yields the same IF as the desired RF, potentially causing interference if not filtered. The LO itself, the desired carrier, or the IF are not the image.