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In television broadcasting, why is Vestigial Sideband (VSB) modulation preferred?

Difficulty: Medium

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
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