*Question G8B02:
What is the term for interference from a signal at twice the IF frequency from the desired signal?*  

*Correct Answer is  B: Image response*  

### AI Response: (may contain errors)  

In radio receivers, the term "image response" refers to interference caused by a signal at twice the intermediate frequency (IF) away from the desired signal. This occurs because the mixer in a superheterodyne receiver can convert two different frequencies to the same IF, leading to potential interference.

1. **Why the correct answer is correct (Image response):**
   - In a superheterodyne receiver, the desired signal is mixed with a local oscillator to produce an intermediate frequency (IF). However, a signal at a frequency that is twice the IF away from the desired signal can also mix with the local oscillator to produce the same IF. This unwanted signal is called the "image frequency," and the interference it causes is known as "image response."

2. **Why the other choices are incorrect:**
   - **Quadrature response (A):** This term is not related to image frequency interference. It typically refers to a method of processing signals in two channels that are 90 degrees out of phase, often used in digital signal processing.
   - **Mixer interference (C):** While mixer interference can include image response, it is a broader term that refers to any unwanted signals produced by the mixing process, not specifically the image frequency.
   - **Intermediate interference (D):** This is not a standard term used to describe interference in radio receivers and does not specifically refer to image frequency issues.

3. **Useful formulas or rules of thumb:**
   - The image frequency ($f_{\text{image}}$) can be calculated as:
     $$f_{\text{image}} = f_{\text{signal}} + 2 \times f_{\text{IF}}$$
   - To minimize image response, receivers often use high-quality RF filters before the mixer to attenuate signals at the image frequency.