*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)  

To understand why received spread spectrum signals are resistant to interference, let's analyze the correct answer and the other options.

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

- **Explanation**: Spread spectrum techniques, such as Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS), spread the signal over a wide frequency range. This makes it less susceptible to narrowband interference because the interference typically affects only a small portion of the spectrum. The receiver can filter out signals that do not match the spread spectrum characteristics, effectively suppressing unwanted signals and allowing the desired signal to be received clearly.

### Why the Other Choices are Incorrect:

- **B: The high power used by a spread spectrum transmitter keeps its signal from being easily overpowered.**
  - **Explanation**: While higher power can improve signal strength, spread spectrum systems typically do not rely on high power for interference resistance. Instead, they use the spreading technique to make the signal more robust against interference. Simply increasing power does not guarantee that the signal will not be overpowered by strong interference.

- **C: Built-in error correction codes minimize interference.**
  - **Explanation**: Error correction codes do help in recovering data that may be corrupted due to interference, but they do not prevent interference from occurring. They are a secondary measure that comes into play after the signal has been received. The primary resistance to interference comes from the spread spectrum technique itself.

- **D: If the receiver detects interference, it will signal the transmitter to change frequencies.**
  - **Explanation**: While some advanced systems may have the capability to change frequencies in response to interference, this is not a fundamental characteristic of all spread spectrum systems. The primary resistance to interference is due to the nature of the spread spectrum technique, not a reactive frequency change.

### Summary:
- Spread spectrum signals are resistant to interference primarily because they spread the signal over a wide frequency range, allowing the receiver to filter out unwanted signals effectively.
- Other options either misinterpret the role of power, error correction, or the dynamic response of the system to interference.

This understanding is crucial for the Extra Class exam, as it highlights the fundamental principles of spread spectrum technology and its advantages in communication systems.