*Question G8A06:
Which of the following is characteristic of QPSK31?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

QPSK31 is a digital mode used in amateur radio communications, and understanding its characteristics is important for the Extra Class exam.

1. **Correct Answer Explanation:**

   - **Sideband Sensitivity:** QPSK31 is sideband sensitive, meaning it requires the correct sideband to be selected for proper decoding. This is because the phase information, which is crucial for QPSK31, can be distorted if the wrong sideband is used.
   
   - **Error Correction:** QPSK31 includes Forward Error Correction (FEC) in its encoding. This helps to correct errors that may occur during transmission, improving the reliability of the communication.
   
   - **Bandwidth:** The bandwidth of QPSK31 is approximately the same as BPSK31. Both modes are designed to fit within a narrow bandwidth, typically around 31 Hz, which makes them efficient for use in crowded band conditions.

2. **Why the Other Choices Are Incorrect:**

   - Each individual choice (A, B, C) is correct on its own, but the question asks for the most comprehensive answer. Since all the characteristics listed (sideband sensitivity, error correction, and similar bandwidth to BPSK31) are true for QPSK31, the correct answer is "All these choices are correct."

3. **Useful Information:**

   - **Bandwidth Comparison:** Both QPSK31 and BPSK31 are narrowband modes, with a bandwidth of approximately 31 Hz. This makes them suitable for low-power, long-distance communications.
   
   - **Error Correction:** The inclusion of error correction in QPSK31 helps mitigate the effects of noise and interference, which is a significant advantage over BPSK31 in certain conditions.

Understanding these characteristics will help you recognize the advantages and limitations of QPSK31 in practical amateur radio operations.