ECE 321-Principles of Communication Systems: Phase Modulation Quiz

Test Your Knowledge of Phase Modulation Concepts

This quiz covers fundamental concepts of phase modulation (PM), a key topic in communication systems for undergraduate electrical engineering students. Answer all 10 questions to test your understanding.

1. What is the fundamental parameter that is varied in phase modulation?
2. The mathematical expression for a phase-modulated wave is:
3. What is the relationship between phase modulation (PM) and frequency modulation (FM)?
4. The phase deviation in PM is directly proportional to:
5. For a single-tone modulating signal m(t) = Amcos(2πfmt), the modulation index (β) for PM is:
6. The bandwidth of a phase-modulated signal according to Carson's rule is approximately:
7. Which of the following is a common method for demodulating phase-modulated signals?
8. In phase modulation, the instantaneous frequency deviation is proportional to:
9. Which statement about PM is correct?
10. In digital phase modulation (PSK), what parameter is varied to represent different symbols?
Question 1 Correct Answer: C
In phase modulation, the phase angle of the carrier wave is varied in proportion to the instantaneous amplitude of the modulating signal. This is the fundamental principle that distinguishes PM from amplitude modulation (AM) and frequency modulation (FM).
Question 2 Correct Answer: B
The standard mathematical representation of a phase-modulated wave is s(t) = Accos(2πfct + kpm(t)), where kp is the phase sensitivity (rad/V) and m(t) is the modulating signal. Option C represents frequency modulation, and option D represents amplitude modulation.
Question 3 Correct Answer: B
Frequency modulation is a special case of phase modulation. When the modulating signal is integrated before phase modulation, the result is frequency modulation. This relationship shows that FM and PM are closely related angle modulation techniques.
Question 4 Correct Answer: A
In phase modulation, the phase deviation (Δθ) is directly proportional to the amplitude of the modulating signal: Δθ = kpm(t), where kp is the phase sensitivity constant and m(t) is the modulating signal.
Question 5 Correct Answer: B
For a single-tone modulating signal m(t) = Amcos(2πfmt), the modulation index (β) for PM is β = kpAm, which represents the maximum phase deviation. For FM, the modulation index would be β = kfAm/fm.
Question 6 Correct Answer: A
Carson's rule provides an approximation for the bandwidth of angle-modulated signals: BW ≈ 2(Δf + fm), where Δf is the maximum frequency deviation and fm is the highest frequency component in the modulating signal.
Question 7 Correct Answer: B
Phase-locked loops (PLLs) are commonly used for demodulating phase-modulated signals. They can track the phase variations of the input signal and reproduce the original modulating signal. Envelope detectors are used for AM, while product detectors are used for DSB-SC and SSB signals.
Question 8 Correct Answer: C
In phase modulation, the instantaneous frequency deviation is proportional to the derivative of the modulating signal. This is because frequency is the derivative of phase with respect to time, so the frequency variation in PM depends on how quickly the phase is changing.
Question 9 Correct Answer: A
Like frequency modulation, phase modulation produces signals with constant amplitude. This property makes PM less susceptible to amplitude-related noise and interference compared to AM, and allows for more efficient power amplification.
Question 10 Correct Answer: C
In phase-shift keying (PSK), a digital modulation scheme based on phase modulation, different phase angles of the carrier wave are used to represent different digital symbols. Common examples include BPSK (2 phases), QPSK (4 phases), and 8-PSK (8 phases).