Why exactly is the signal not down converted directly to the 1st Nyquist zone?

On behalf of Del Jones:
For the design example shown in the webcast, in order to get the band of interest into the 1rs Nyquist zone, we would need to have a sample rate of 4Gsps, which is beyond the capability of the AD9208.  As for down conversion, that occurs after sampling.  In order to retain all of the information in the signal being sampled, we have to sample something in the 2st Nyquist zone, which, in this case, is the aliased images of the band of interest.  Down conversion is performed to get this image down to DC, to ease the filter design, not to assist in the sampling.