*Question E8D01:
Why are received spread spectrum signals resistant to interference?*  

*Correct Answer is  A: Signals not using the spread spectrum algorithm are suppressed in the receiver*  

### AI Response: (may contain errors)  

Spread spectrum signals are designed to be resistant to interference by spreading the signal over a wide frequency range. This technique makes it difficult for narrowband interference to affect the signal significantly.

### Explanation of the Correct Answer:
- **Correct Answer: A**  
  Spread spectrum signals use a specific algorithm to spread the signal across a wide frequency band. The receiver, which knows this algorithm, can despread the signal and recover the original data. Signals that do not use the same spread spectrum algorithm appear as noise and are suppressed by the receiver. This is why spread spectrum signals are resistant to interference from other signals that do not use the same spreading code.

### Why the Other Choices are Incorrect:
- **Choice B: The high power used by a spread spectrum transmitter keeps its signal from being easily overpowered**  
  This is incorrect because spread spectrum does not rely on high power to resist interference. Instead, it uses the spreading technique to make the signal robust against interference.

- **Choice C: Built-in error correction codes minimize interference**  
  While error correction codes can help recover data in the presence of errors, they are not the primary reason spread spectrum signals resist interference. The key factor is the spreading of the signal across a wide frequency range.

- **Choice D: If the receiver detects interference, it will signal the transmitter to change frequencies**  
  This describes a frequency-hopping spread spectrum technique, but it is not the primary reason for interference resistance. The main reason is the spreading of the signal, which makes it less susceptible to narrowband interference.

### Useful Concepts:
- **Spread Spectrum**: A technique where a signal is spread over a wide frequency band, making it less susceptible to interference and eavesdropping.
- **Despreading**: The process by which the receiver uses the same spreading code to recover the original signal from the spread spectrum signal.

Understanding these concepts will help you grasp why spread spectrum signals are inherently resistant to interference.