*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)  

Direct sequence spread spectrum (DSSS) is the correct answer because it uses a high-speed binary bit stream, known as a pseudo-random noise (PN) sequence, to directly modulate the phase of an RF carrier. This technique spreads the signal over a wider bandwidth, making it more resistant to interference and eavesdropping.

### Explanation:

1. **Direct Sequence (Correct Answer):**
   - In DSSS, each bit of the original data is multiplied by a much faster sequence of bits (the PN sequence). This process spreads the signal across a wider frequency band.
   - The phase of the RF carrier is shifted according to the PN sequence, effectively spreading the signal.

2. **Why Other Choices Are Incorrect:**
   - **Frequency Hopping (Choice A):** 
     - This technique rapidly changes the carrier frequency among many frequencies within a large bandwidth. It does not involve shifting the phase of the RF carrier with a high-speed bit stream.
   - **Binary Phase-Shift Keying (Choice C):**
     - BPSK is a modulation technique where the phase of the carrier is shifted to represent data bits, but it does not use a high-speed binary bit stream to spread the signal over a wide bandwidth.
   - **Phase Compandored Spread Spectrum (Choice D):**
     - This is not a standard spread spectrum technique and does not involve using a high-speed binary bit stream to shift the phase of an RF carrier.

### Key Points:
- **DSSS**: Uses a PN sequence to spread the signal by phase-shifting the carrier.
- **Frequency Hopping**: Changes frequencies, not phases.
- **BPSK**: Modulates phase for data, not for spreading.
- **Phase Compandored**: Not a recognized technique in this context.

Understanding these distinctions helps in identifying the correct spread spectrum technique used in the question.