*Question E8D03:
Which describes spread spectrum frequency hopping?*  

*Correct Answer is  D: Rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence*  

### AI Response: (may contain errors)  

To understand spread spectrum frequency hopping, let's break down the correct answer and the other choices.

### Correct Answer: 
**D: Rapidly varying the frequency of a transmitted signal according to a pseudorandom sequence.**

- **Explanation**: 
  - In frequency hopping spread spectrum (FHSS), the transmitter changes its frequency at regular intervals according to a pseudorandom sequence. This technique helps to minimize interference and avoid detection, as the signal hops between different frequencies within a designated band. The pseudorandom nature of the hopping sequence ensures that the receiver can predict the frequency changes, allowing for effective communication.

### Why the Other Choices are Incorrect:

- **A: If interference is detected by the receiver, it will signal the transmitter to change frequencies.**
  - **Explanation**: This describes a reactive approach to interference, which is not how frequency hopping works. In FHSS, the frequency changes are predetermined by the pseudorandom sequence, not based on real-time interference detection.

- **B: RF signals are clipped to generate a wide band of harmonics which provides redundancy to correct errors.**
  - **Explanation**: This describes a different technique known as direct sequence spread spectrum (DSSS), where the signal is spread by modulating it with a higher rate bit stream. Clipping is not a method used in frequency hopping.

- **C: A binary bit stream is used to shift the phase of an RF carrier very rapidly in a pseudorandom sequence.**
  - **Explanation**: This describes phase shift keying (PSK) rather than frequency hopping. While both techniques can be used in spread spectrum communications, frequency hopping specifically involves changing the frequency, not the phase.

### Summary:
- **Frequency Hopping**: Involves rapidly changing the frequency of the transmitted signal based on a pseudorandom sequence.
- **Key Concept**: The pseudorandom sequence allows both the transmitter and receiver to stay synchronized without needing to react to interference.

This understanding of frequency hopping will help you in the Extra Class exam and in practical applications of amateur radio.