*Question E4C02:
Which of the following receiver circuits can be effective in eliminating interference from strong out-of-band signals?*  

*Correct Answer is  A: A front-end filter or preselector*  

### AI Response: (may contain errors)  

To understand why a front-end filter or preselector is effective in eliminating interference from strong out-of-band signals, let's break down the options:

### Correct Answer: A front-end filter or preselector

- **Explanation**: A front-end filter or preselector is designed to allow only a specific range of frequencies to pass through while attenuating (reducing) signals outside that range. This is particularly useful for rejecting strong out-of-band signals that can cause interference in the receiver. By filtering out unwanted frequencies before they reach the main receiver circuitry, the front-end filter enhances the overall selectivity and sensitivity of the receiver.

### Why the Other Choices are Incorrect:

- **B: A narrow IF filter**  
  - **Explanation**: While a narrow Intermediate Frequency (IF) filter can help in rejecting signals that are close to the desired frequency, it is not as effective against strong out-of-band signals. If the out-of-band signals are significantly stronger, they can still cause intermodulation or desensitization issues before the signal reaches the IF stage.

- **C: A notch filter**  
  - **Explanation**: A notch filter is designed to reject a very specific frequency (or narrow band of frequencies) while allowing others to pass. This is useful for eliminating specific interference (like a known tone or signal), but it does not provide broad-spectrum protection against strong out-of-band signals.

- **D: A properly adjusted product detector**  
  - **Explanation**: A product detector is used in demodulating signals, particularly in SSB (Single Sideband) and other modulation schemes. While it can help in recovering the desired signal from a modulated carrier, it does not inherently filter out strong out-of-band signals. Its primary function is not interference rejection but signal demodulation.

### Summary

- **Front-end filters or preselectors** are essential for rejecting unwanted strong out-of-band signals before they can interfere with the receiver's performance.
- **Narrow IF filters**, **notch filters**, and **product detectors** serve different purposes and are not as effective in addressing the issue of strong out-of-band interference.

This understanding is crucial for selecting the right components in a receiver design to ensure optimal performance in the presence of interference.