*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)  

Spread spectrum frequency hopping is a technique used in wireless communications to enhance security and reduce interference. Let's break down the correct answer and why the other choices are incorrect:

### 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 rapidly among many channels, following a sequence that appears random but is actually predetermined (pseudorandom). This makes the signal more resistant to interference and eavesdropping because an unintended receiver would need to know the hopping sequence to follow the signal.

### Why Other Choices Are Incorrect:

- **Choice A**: "If interference is detected by the receiver, it will signal the transmitter to change frequencies"
  - **Explanation**: This describes a reactive interference management technique, not spread spectrum. FHSS does not rely on interference detection to change frequencies; it follows a predetermined sequence regardless of interference.

- **Choice B**: "RF signals are clipped to generate a wide band of harmonics which provides redundancy to correct errors"
  - **Explanation**: This describes a method of generating harmonics, not frequency hopping. Clipping signals to create harmonics is unrelated to the concept of spread spectrum.

- **Choice 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, specifically a form of spread spectrum called Direct Sequence Spread Spectrum (DSSS), not frequency hopping. DSSS spreads the signal by modulating it with a pseudorandom bit sequence, affecting the phase rather than the frequency.

### Key Points:
- **FHSS**: Involves changing frequencies rapidly in a pseudorandom manner.
- **DSSS**: Involves spreading the signal by modulating it with a pseudorandom bit sequence, affecting the phase.

Understanding these distinctions is crucial for identifying the correct spread spectrum technique in exam questions.