*Question E7E06:
Why is de-emphasis used in FM communications receivers?*  

*Correct Answer is  A: For compatibility with transmitters using phase modulation*  

### AI Response: (may contain errors)  

De-emphasis in FM communications receivers is primarily used to improve the quality of the received audio signal by compensating for the pre-emphasis applied at the transmitter. Here's a breakdown of the correct answer and the other choices:

### Correct Answer: A - For compatibility with transmitters using phase modulation

- **Explanation**: 
  - De-emphasis is used to counteract the effects of pre-emphasis, which boosts higher frequencies during transmission. This is done to improve the signal-to-noise ratio for those frequencies. When the signal is received, de-emphasis reduces the higher frequencies back to their original levels, ensuring compatibility with phase modulation systems and improving overall audio quality.

### Why the Other Choices are Incorrect:

- **B: To reduce impulse noise reception**  
  - While de-emphasis can help in reducing the impact of noise, its primary purpose is not specifically to reduce impulse noise. Other techniques, such as filtering, are more effective for that purpose.

- **C: For higher efficiency**  
  - De-emphasis does not directly relate to the efficiency of the transmission or reception process. Its main role is in signal fidelity rather than efficiency.

- **D: To remove third-order distortion products**  
  - De-emphasis is not designed to remove distortion products. It is focused on frequency response adjustments rather than distortion correction.

### Summary

- De-emphasis is essential for maintaining audio quality in FM communications by ensuring that the signal received matches the intended audio output after pre-emphasis is applied at the transmitter. 

This understanding is crucial for the Extra Class exam, as it highlights the importance of signal processing techniques in radio communications.