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Scrambling

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Ex Member
Ex Member


Mar 4th, 2011 at 11:46am  
Could anyone kindly explain briefly about scrambling function and why it's necessary. If any animated example is available would be great.

looking Forward

Regards,

Akki
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Eric Johnston
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Posts: 2109
Reply #1 - Mar 4th, 2011 at 12:51pm  
Scrambling serves two purposes:

It stops long sequences of 1s or 0s occurring in the transmitted carrier.  If user data consisting of all 1s or all 0s was allowed through to the modulator, the transmitted carrier would be steady and the demodulator clock at the far end would soon loose count of the exact number of 1s or 0s as it would have nothing to synchronise with.

It also makes the spectrum noise-like, spread out nicely, with a smooth power spectral density so that it causes minimal interference. If you turn the scambling off, the carrier has lots of high spectral density spikes which interfere with other services.

Scrambling does not provide privacy as the logic of the process (polynomial) is publically known. Many demodulators have all the various polynomial options in the firmware. Scrambling is not encryption.

Read more http://en.wikipedia.org/wiki/Scrambler
wxw
Best regards, Eric.
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Ex Member
Ex Member


Reply #2 - Mar 4th, 2011 at 7:38pm  
thx mr.eric
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