Why video signal is frequency modulated in satellite communication?

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  • Why video signal is frequency modulated in satellite communication?


Answer #1 | 30/04 2017 02:01
Sometimes yes and other times it may be Amplitude M or Phase Modulated.
Answer #2 | 02/05 2017 16:21
Satellites use non-linear amplifiers to relay signals back to earth. Using AM for any type of transmission through the satellite would heavily distort the AM signal and make the signal have very poor quality. Video, or more accurately TV signals used to be exclusively distributed via satellite using FM because of its constant envelope characteristic made them largely impervious to the amplitude distortions caused by the non-linear amplification of the satellite. However, increasingly more video (TV) transmissions are using digital transmission schemes. Here the baseband TV signal is digitized into some bit format and the bits are used to phase-modulate (PM) the carrier. When PM is digitally modulated it is known as Phase Shift Keying or PSK. This also has a constant envelope characteristic like FM and PM making it suitable for the non-linear amplification of the satellite. Satellite amplifiers are becoming more and more powerful as the technology improves. They also are becoming more linearized. This is allowing digital transmissions to utilize a combination PSK and AM technique known as APSK or sometimes, QAM (Quadrature Amplitude Modulation). Using these techniques requires the satellite amplifiers to be used at much less than their full power, so they are linear and do not cause large amplitude distortions. This is done because these newer techniques allow more bits/sec to be transmitted on the satellite channel. This allows higher quality video (HDTV for example) or just more video signals per satellite channel.
Answer #3 | 30/04 2017 04:09
Wide band FM at that. The wide band FM allowed the receiver to be tuned a little off center (or to drift) without any significant affect on the received signal.

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