In television broadcasting, why is Vestigial Sideband (VSB) modulation preferred?
Electronics and Communication Engineering
Communication Systems
Difficulty: Medium
Choose an option
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Ait reduces the bandwidth requirement to half
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Bit avoids phase distortion at low frequencies
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Cit results in better reception
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Dnone of the above
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Eit simplifies antenna design
Answer
Correct Answer: it avoids phase distortion at low frequencies
Explanation
Introduction / Context:VSB modulation is a compromise between AM (double sideband) and SSB (single sideband). It is commonly used in TV broadcasting for video signals that have a wide baseband spectrum.
Given Data / Assumptions:
- Full AM doubles bandwidth.
- SSB saves bandwidth but complicates filtering.
Concept / Approach:VSB transmits one sideband fully and the other partially, ensuring that low-frequency components are preserved without distortion while reducing bandwidth.
Step-by-Step Solution:
TV video baseband ≈ 0–5 MHz.SSB filtering near 0 Hz is problematic → causes distortion.VSB retains a 'vestige' of the second sideband near DC, preventing distortion at low frequencies.Verification / Alternative check:TV standards (NTSC, PAL) explicitly specify VSB for this reason.
Why Other Options Are Wrong:
Half bandwidth reduction: not exact, VSB still > SSB.Better reception: a vague benefit, not the technical reason.Antenna design is unrelated.Common Pitfalls:
Confusing bandwidth efficiency with distortion control.Final Answer:
it avoids phase distortion at low frequencies