Quote:
Originally Posted by Sephiroth
Not being clued up on the insides of VM cable, I was surprised to see the word "analogue" there. Now, you're rarely wrong at this level of discussion. So any further knowledge tap from you would be appreciated.
Since analogue bandwidth is several times larger than digital channels and I'm told that RG (where I'm served by VM) is a digital solution, I would have expected to see digital bit streams (especially because of HDTV) modulated by QAM.
So what's this analogue stuff?
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QAM is analogue, and the bit streams are encoded into QAM channels. Pure digital / baseband has a spectral efficiency of 1 bit per Hz, 256QAM has an efficiency of 8 bits per Hz. No real competition.
Analogue TV is 8MHz per channel, digital TV is digital streams encoded into analogue for transport. Once the QAM has been decoded it will produce 1s and 0s.
http://en.wikipedia.org/wiki/Quadrat...ude_modulation
This is a nice image.
Each grouping in the lower right indicates 8 bits of data, there are 256 possible points in the constellation, 2 ^ 8 = 256. The signal that arrives at the decoder is actually 2 signals 90 degrees apart in phase, the decode splits them and decodes them, one into the horizontal axis on the constellation, one into the vertical axis, 16 possible values for each signal, that produces the 8 bits per Hz.