The way I understand it, is that to avoid aliasing on an ADC, you have to be in the first Nyquist zone (so half the sampling speed). What doesn't make sense to me is how the Hackrf is able to bypass this, and achieve 20MHz of bandwidth, even though the 1st Nyquist zone would be only 11MHz.
I notice from the schematics that the MAX5864 ADC is two channels, with the baseband I signal going into one channel, and the baseband Q signal going into another. Do the two channels get added together, to form an overall bandwidth of 20MHz?
Also, while I'm at it, what exactly is the purpose of using in an sdr? Is it to make modulation/demodulation easier?