Question
Which of the following is characteristic of QPSK31?
Answer Options
- A) It is sideband sensitive
- B) Its encoding provides error correction
- C) Its bandwidth is approximately the same as BPSK31
- D) All these choices are correct
Correct Answer: A
Explanation
QPSK31 (Quadrature Phase Shift Keying at 31 baud) is a digital mode that conveys information by shifting the carrier’s phase to one of four possible states (0^\circ, 90^\circ, 180^\circ, 270^\circ). Because it is a phase-based modulation system implemented using a suppressed carrier, it is highly sensitive to the proper demodulation process.
Crucially, QPSK31 is sideband sensitive. If the receiving station incorrectly selects the wrong sideband (USB instead of LSB or vice-versa), the signal will be phase-inverted and cannot be decoded correctly. In contrast, BPSK31 (Binary PSK) is not sideband sensitive.
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