Question
Which of the following describes the use of vestigial sideband in analog fast-scan TV transmissions?
Answer Options
- A) The vestigial sideband carries the audio information
- B) The vestigial sideband contains chroma information
- C) Vestigial sideband reduces the bandwidth while increasing the fidelity of low frequency video components
- D) Vestigial sideband provides high frequency emphasis to sharpen the picture
Correct Answer: C
Explanation
Analog Fast-Scan TV (FSTV) signals, typically following the NTSC standard, require substantial bandwidth (up to 6 MHz). Pure double-sideband (DSB) AM modulation would require 8 to 12 MHz, which is spectrally inefficient. Vestigial Sideband (VSB) modulation is a technique used to compress the signal into the allotted 6 MHz channel while retaining image quality.
VSB works by transmitting one complete sideband, the carrier, and only a ‘vestige’ (a portion) of the second sideband. This partial sideband transmission effectively reduces the overall bandwidth while improving the fidelity of the low-frequency video components. The low-frequency signals near the carrier (which carry much of the image’s detail) benefit from the transmission of a significant portion of both sidebands, which compensates for the reduction in bandwidth compared to full DSB.
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