General exam question G8A12
Subelement G8, SIGNALS AND EMISSIONS· Group G8A
What is QPSK modulation?
- A.Modulation using quasi-parallel to serial conversion to reduce bandwidth
- B.Modulation using quadra-pole sideband keying to generate spread spectrum signals
- C.Modulation using Fast Fourier Transforms to generate frequencies at the first, second, third, and fourth harmonics of the carrier frequency to improve noise immunity
- D.Modulation in which digital data is transmitted using 0-, 90-, 180- and 270-degrees phase shift to represent pairs of bits (correct answer)
WhyQPSK modulation transmits digital data using 0, 90, 180, and 270 degree phase shifts to represent pairs of bits. QPSK transmits data by shifting the carrier's phase among four distinct positions, 0, 90, 180, and 270 degrees, with each phase state representing a unique pair of data bits, answer D. It has nothing to do with parallel-to-serial conversion, isn't a spread-spectrum sideband-keying technique, and doesn't generate harmonic-frequency tones via an FFT, so A, B, and C misdescribe what QPSK actually is.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2023-2027 NCVEC Element 3 pool (public domain); the explanation above is original writing, see our methodology.
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