*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 eliminate interference from strong out-of-band signals, a front-end filter or preselector is effective. Here's why:

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

- **Front-end Filter/Preselector**: This circuit is placed at the very beginning of the receiver's signal path. It selectively allows only the desired frequency range to pass through while attenuating signals outside this range. This helps prevent strong out-of-band signals from overloading the receiver's front-end, which can cause distortion or desensitization.

### Why Other Choices Are Incorrect:

- **B: A narrow IF filter**: 
  - An Intermediate Frequency (IF) filter is used to improve selectivity by narrowing the bandwidth of the received signal. However, it operates after the initial stages of the receiver, so it does not prevent strong out-of-band signals from entering the receiver and potentially causing interference.

- **C: A notch filter**: 
  - A notch filter is designed to attenuate a specific frequency or narrow band of frequencies. While useful for eliminating specific unwanted signals, it is not effective for broad out-of-band interference, as it targets only a narrow frequency range.

- **D: A properly adjusted product detector**: 
  - A product detector is used for demodulating signals, particularly in SSB and CW modes. It does not have any filtering capability to eliminate out-of-band signals, as it operates on the signal after it has been converted to an intermediate frequency.

### Summary

A front-end filter or preselector is crucial for preventing strong out-of-band signals from entering the receiver and causing interference. It acts as the first line of defense by filtering out unwanted frequencies before they can affect the receiver's performance.