*Question E8D02:
What spread spectrum communications technique uses a high-speed binary bit stream to shift the phase of an RF carrier?*  

*Correct Answer is  B: Direct sequence*  

### AI Response: (may contain errors)  

The correct answer to the question is **B: Direct sequence**. Here's why:

### Explanation of the Correct Answer:
- **Direct Sequence Spread Spectrum (DSSS)** uses a high-speed binary bit stream to modulate the phase of an RF carrier. In this technique, each bit of the data is represented by multiple bits of the spreading code, which effectively spreads the signal over a wider bandwidth. This is achieved by multiplying the data signal with a pseudo-random noise (PN) sequence, which shifts the phase of the carrier signal according to the bits of the PN sequence.

### Why the Other Choices are Incorrect:
- **A: Frequency hopping**  
  - This technique involves rapidly switching the carrier frequency among many frequency channels, using a predetermined sequence. It does not primarily shift the phase of the RF carrier but changes the frequency.

- **C: Binary phase-shift keying (BPSK)**  
  - BPSK is a modulation scheme that uses two phases to represent binary data. While it does involve phase shifting, it does not use a high-speed binary bit stream to spread the signal over a wider bandwidth like DSSS does.

- **D: Phase compandored spread spectrum**  
  - This technique combines phase modulation with companding (compressing and expanding) to improve the signal-to-noise ratio. However, it does not specifically use a high-speed binary bit stream to shift the phase of the RF carrier in the same way that DSSS does.

### Summary:
- **Direct Sequence Spread Spectrum (DSSS)** is the correct answer because it directly uses a high-speed binary bit stream to modulate the phase of the RF carrier.
- The other options either focus on different modulation techniques or methods that do not involve the same phase modulation characteristics as DSSS.

This understanding of spread spectrum techniques is crucial for the Extra Class exam, as it highlights the differences in modulation methods and their applications in communications.