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RE: DSP Possibilities ?



I think your bits/hz calculations are with FEC. Uncoded QPSK would produce 
2 bits/Hz, 8PSK without coding is 3 bits/Hz and 16QAM is 4 bits/Hz. This 
would reduce the transmitted symbol rate to the data rate divided by the 
number of bits/Hz. Of course, I can't imagine using these schemes on 
amateur satellites (or any other satellites for that fact) without some 
FEC.

 I could be wrong, but I don't think changing the modulation effects the 
sample rate for the modulator, but it does increase the work load from a 
number crunching view. On the other hand, the demodulator's sampling rate 
should be lower due to the decreased symbol rate.  I would imagine that the 
number crunching inside the demod would also increase. The net sum result 
is that if you take some of the burden off the sample rate, you use up the 
processing power somewhere else, and it's most likely NOT a linear 
tradeoff...

Howie
AB2S

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