Thanks for the thorough explanation US. Do you mean 24/7 sampling at 3+ GHz could be taking place in the sat? I understand the reasoning but doubt the practicalities.
No. At an earth station the incoming RF effectively filtered and downconverted to extract a section of the RF they care about. This downconvered segment is called an IF, and will be a much much smaller chunk of bandwidth.
So the sampling is done on earth, and it is done over a subset of the spectrum.