Question
What is the term for interference from a signal at twice the IF frequency from the desired signal?
Answer Options
- A) Quadrature response
- B) Image response
- C) Mixer interference
- D) Intermediate interference
Correct Answer: B
Explanation
In a superheterodyne receiver, the mixer produces the desired Intermediate Frequency (IF) from the difference between the received RF signal (F_{\text{RF}}) and the Local Oscillator (F_{\text{LO}}). However, a second, unwanted RF signal (F_{\text{IMAGE}}) can also produce the same IF frequency, and this unwanted signal is called the image frequency.
The image frequency always exists at a distance of twice the IF frequency from the desired signal (F_{\text{IMAGE}} = F_{\text{RF}} + 2 F_{\text{IF}} or F_{\text{RF}} - 2 F_{\text{IF}}). Interference caused by a strong signal at this image frequency is called image response. This requires a pre-selector filter before the mixer to attenuate the image frequency and prevent it from reaching the mixer stage.
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