In TV transmission, the picture signal is amplitude-modulated and the sound signal is frequency-modulated. This is done because

Question

In TV transmission, the picture signal is amplitude-modulated and the sound signal is frequency-modulated. This is done because

1. A. it is not possible to frequency modulate the picture signal.
2. B. bandwidth requirement is minimized (Correct answer)
3. C. Sound signal is more susceptible to noise than a picture signal.
4. D. synchronization of picture frames becomes easier.

Correct Answer

Option B — bandwidth requirement is minimized

Detailed Solution & Explanation

The correct answer is bandwidth requirement is minimized.

Key Points

• The video signal occupies a very wide baseband — up to about 5 MHz. Frequency modulating it would require several times that bandwidth, which no television channel could accommodate, so AM (in vestigial sideband form) is used instead.
• The sound signal is narrow by comparison, only a few kHz wide, so it can be frequency modulated cheaply while gaining FM's noise immunity.
• Choosing the modulation scheme to suit each signal keeps the total channel bandwidth to a minimum.

Additional Information

• Note that FM's better noise performance for the sound channel is a genuine secondary benefit; the primary engineering driver, however, is the bandwidth economy that this combination achieves.
• A complete analogue TV channel fits into 6, 7 or 8 MHz only because the picture uses vestigial sideband AM.