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Originally Posted by dapack5
what is the difference in these tuners? is 8vsb an OTA tuner only?
have seen one of each listed on fleabay
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Sorry for responding to a very old post, but I noticed this, and I think the response didn't quite address the question, and I think it is an interesting topic that had me confused too.
8VSB and 8PSK are completely different things, and I think you are right, that 8vsb is for OTA. It is the format used for the ATSC digital
HD OTA channels. I don't pretend to understand even 1% of what is going on, but it is my understanding that an OTA TV signal is AM modulated, and has sidebands, and 8vsb is something similar to SSB, in that in an AM modulated signal, a lot of information in the signal is duplicated, so you can send the necessary information to regenerate the signal at the receiver in less bandwidth by filtering out the main carrier and duplicated sidebands. That's about the extent of my limited knowledge on that, but you can read more at
http://www.broadcast.net/~sbe1/8vsb/8vsb.htm .
Re the 8PSK, this is a mode used in satellite, and as best as I can understand, is more similar to an FM signal than an AM signal. The modulation is phase shifted onto a carrier at 8 different angles rather than 4 as in the QPSK, so that you can get twice the data onto the same signal. However since the different phase angles are closer together, it is much more susceptible to noise so it requires a much cleaner signal. To get the cleaner signal, you either need a much more powerful satellite, wider spacing between the sats to reduce interferrence, larger dishes {as the other response suggested} to give more resolution from adjacent satellites and/or operation at higher frequencies to give better resolution with the same sized dish. As I understand it, {likely innacurate} if 8PSK is done on conventional C/Ku sats, most consumer dishes are too small to give the resolution requirred to give a clean signal. However the DBS sats like Dish Net and DTV, are spaced wide enough apart that they can utilize this technique with consumer dishes. I think that Dishnet is employing 8PSK for it's HD signals.
Anyway, that's my impression, and I know next to nothing about either mode, so anyone who sees errors, please correct me.