*Question G4A07:
What happens as a receiver’s noise reduction control level is increased?*  

*Correct Answer is  A: Received signals may become distorted*  

### AI Response: (may contain errors)  

As a receiver's noise reduction control level is increased, the correct answer is:

**A: Received signals may become distorted.**

### Explanation of the Correct Answer:
- **Distortion of Received Signals**: Increasing the noise reduction control level can lead to the suppression of not only noise but also weak signals. This can result in distortion, especially if the control is set too high, causing the receiver to misinterpret the signal's characteristics. The receiver may filter out parts of the signal that are essential for proper demodulation, leading to a loss of fidelity.

### Explanation of Incorrect Choices:
- **B: Received frequency may become unstable**: 
  - This is incorrect because increasing noise reduction does not inherently affect the stability of the received frequency. Frequency stability is more related to the local oscillator and the design of the receiver rather than noise reduction settings.

- **C: CW signals may become severely attenuated**: 
  - While it is true that noise reduction can affect weak signals, CW (Continuous Wave) signals are typically robust against noise. Increasing noise reduction may not specifically lead to severe attenuation of CW signals; rather, it may distort them, as mentioned in the correct answer.

- **D: Received frequency may shift several kHz**: 
  - This choice is incorrect because noise reduction controls do not cause frequency shifts. Frequency shifts are usually a result of issues like Doppler effect, local oscillator drift, or improper tuning, not noise reduction settings.

### Summary:
- Increasing the noise reduction control can distort received signals by filtering out important signal components.
- The other options do not accurately describe the effects of adjusting the noise reduction control.

### Useful Rule of Thumb:
- When using noise reduction features, start with a lower setting and gradually increase it while monitoring the signal quality to avoid distortion.