TROOPER
09-29-2008, 04:40 PM
i remember talking about this quite a few months back and had to dig it up again so people can read since i was asked a few times again about the differences between the 3 and differences between 8psk and Qpsk
Mpeg2 is encoding, like mpeg4 is (xvid, divx, H.264, x264, etc)
Nagravision is encryption
QPSK/8PSK is modulation
All 3 are 100% different, nothing to do with each other
The signal they send is Mpeg2
but they don't send 1's and 0's
that wouldn't work
they need to transform that in a suitable analog waveform first
so that signal, "normally" they take 2 bits from it, and transform that into one of 4 voltages (levels)
that's quadrature (as in 4) phase shift keying (QPSK)
2 bits, = 4 states
so for every symbol a transponder sends (usually 20 million symbols per second)
that sends 2 bits
so 40MBit per sec
but, what if you want more to fit on there?
that's where you move to other modulation types
8PSK is another one of them
now you take 3 bits, and transform that into 8 levels (2^3 is 8)
now you have 20M samples * 3 bits/sample, or 60MBit!
BUT, normally, to be able to use that, you need a stronger signal
or bigger dishes
as with 8 levels, you only have half as much voltage between the different states
so it has to have less noise/higher quality
that's where the turbo part comes in
which lets them use it, on the exact same equipment (no higher powered sat, no bigger dishes), with more error correction
so they don't get quite 50% extra out of it, perhaps more like 35%
but it's still 35% extra bandwidth, on the same sats and dishes
35% extra BW, out of a bird with 32 TPs, is like having an extra 11 transponders' worth of bandwidth all of a sudden
so more channels, without launching new sats
the 8psk module, is a 8PSK modulator, because the QPSK demodulator in normal boxes, have no idea wtf them 8 levels do
that fancy 8PSK demod on the module, takes the 8 levels, and converts it back to 3 bits for each symbol
which the QPSK would never be able to do
that's why all the ppl that ask if it couldn't be done in software makes me laugh
the QPSK demod chip can't even turn the damn 8PSK RF waveform/signal into 1's and 0's, i dunno what they expect the box to do with no data
past 8 levels, we don't use phase shift keying anymore, but things like quadrature amplitude modulation e.g. 16QAM
but then again, we'd need higher powered sats, or bigger dishes everywhere
but one extra bit out of each symbol (4 instead of 3), so only 33% increase tops, and massive equipment swaps required
Mpeg2 is encoding, like mpeg4 is (xvid, divx, H.264, x264, etc)
Nagravision is encryption
QPSK/8PSK is modulation
All 3 are 100% different, nothing to do with each other
The signal they send is Mpeg2
but they don't send 1's and 0's
that wouldn't work
they need to transform that in a suitable analog waveform first
so that signal, "normally" they take 2 bits from it, and transform that into one of 4 voltages (levels)
that's quadrature (as in 4) phase shift keying (QPSK)
2 bits, = 4 states
so for every symbol a transponder sends (usually 20 million symbols per second)
that sends 2 bits
so 40MBit per sec
but, what if you want more to fit on there?
that's where you move to other modulation types
8PSK is another one of them
now you take 3 bits, and transform that into 8 levels (2^3 is 8)
now you have 20M samples * 3 bits/sample, or 60MBit!
BUT, normally, to be able to use that, you need a stronger signal
or bigger dishes
as with 8 levels, you only have half as much voltage between the different states
so it has to have less noise/higher quality
that's where the turbo part comes in
which lets them use it, on the exact same equipment (no higher powered sat, no bigger dishes), with more error correction
so they don't get quite 50% extra out of it, perhaps more like 35%
but it's still 35% extra bandwidth, on the same sats and dishes
35% extra BW, out of a bird with 32 TPs, is like having an extra 11 transponders' worth of bandwidth all of a sudden
so more channels, without launching new sats
the 8psk module, is a 8PSK modulator, because the QPSK demodulator in normal boxes, have no idea wtf them 8 levels do
that fancy 8PSK demod on the module, takes the 8 levels, and converts it back to 3 bits for each symbol
which the QPSK would never be able to do
that's why all the ppl that ask if it couldn't be done in software makes me laugh
the QPSK demod chip can't even turn the damn 8PSK RF waveform/signal into 1's and 0's, i dunno what they expect the box to do with no data
past 8 levels, we don't use phase shift keying anymore, but things like quadrature amplitude modulation e.g. 16QAM
but then again, we'd need higher powered sats, or bigger dishes everywhere
but one extra bit out of each symbol (4 instead of 3), so only 33% increase tops, and massive equipment swaps required