Match communication systems/receivers to their characteristic techniques. List I List II A. Costas receiver 1. Vestigial sideband (VSB) B. Stereo multiplexing (radio) 2. Demodulating DSB-SC (coherent) C. TV broadcasting 3. FM radio broadcasting (multiplex)
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AA-1, B-3, C-2
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BA-2, B-3, C-1
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CA-2, B-1, C-4
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DA-4, B-3, C-1
Answer
Correct Answer: A-2, B-3, C-1
Explanation
Introduction / Context:Different communication services use different modulation/detection methods. Matching them quickly is a staple of communications examinations and interviews.
Given Data / Assumptions:
- Costas loop is a coherent detector for DSB-SC or suppressed-carrier systems.
- FM stereo broadcasting uses multiplexing (L+R, L−R with a pilot).
- Analog TV broadcasting traditionally used AM-VSB for the video channel.
Concept / Approach:
Map each system to the defining modulation/detection method: Costas→DSB-SC demodulation, stereo multiplex→FM radio system, TV broadcast→VSB to reduce bandwidth while maintaining low-frequency fidelity.
Step-by-Step Solution:
Recognize the Costas receiver as a PLL-based coherent detector for suppressed carriers ⇒ A-2.Recall FM stereo uses a 19 kHz pilot and 38 kHz subcarrier for L−R ⇒ B-3.Recall broadcast TV used VSB AM for video to conserve spectrum ⇒ C-1.Verification / Alternative check:
Block diagrams in standard texts show Costas loops recovering carrier phase; FM stereo multiplex standards (e.g., 75 kHz deviation, pilot) validate B; NTSC/PAL video spectrum masks show VSB, confirming C.
Why Other Options Are Wrong:
- Assigning VSB to FM stereo is incorrect; FM multiplex does not use vestigial sidebands.
- Claiming Costas is for VSB confuses coherent DSB-SC detection with amplitude filtering techniques.
Common Pitfalls:
Mixing up Costas with a simple envelope detector; the latter requires an unsuppressed carrier and is not suitable for DSB-SC.
Final Answer:
A-2, B-3, C-1