*Question E4D09:
What is the purpose of the preselector in a communications receiver?*  

*Correct Answer is  C: To increase the rejection of signals outside the band being received*  

### AI Response: (may contain errors)  

The correct answer to the question about the purpose of the preselector in a communications receiver is:

**C: To increase the rejection of signals outside the band being received.**

### Explanation of the Correct Answer:
- A preselector is a filter that is used in a communications receiver to allow only the desired frequency range to pass through while rejecting unwanted signals outside that range. 
- This helps to improve the overall selectivity of the receiver, reducing interference from signals that are not in the desired frequency band. 

### Why the Other Choices are Incorrect:
- **A: To store frequencies that are often used**  
  This is incorrect because a preselector does not store frequencies; it filters them. Frequency storage is typically handled by memory functions in the receiver, not by the preselector.

- **B: To provide broadband attenuation before the first RF stage to prevent intermodulation**  
  While a preselector can help reduce unwanted signals, its primary function is not to provide broadband attenuation. Instead, it selectively filters frequencies, which may indirectly help with intermodulation by reducing out-of-band signals.

- **D: To allow selection of the optimum RF amplifier device**  
  This is incorrect because the preselector does not select RF amplifier devices. The choice of RF amplifier is based on other design considerations, not on the function of the preselector.

### Useful Concepts:
- **Selectivity**: The ability of a receiver to differentiate between the desired signal and unwanted signals. A preselector enhances selectivity by filtering out-of-band signals.
- **Intermodulation**: A phenomenon where two or more signals mix in a non-linear device, creating additional unwanted frequencies. By using a preselector, you can minimize the chances of intermodulation products affecting the desired signal.

In summary, the preselector is crucial for improving the performance of a communications receiver by ensuring that only the desired signals are amplified and processed, thus enhancing the clarity and quality of the received communication.