HF sucks. It is full of very large signals that will typically hurt
this kind of system (12 bit front
end). You have to scale to handle the largest signal and the weaker
ones go off the bottom, even
after processing gain through the DDC. If you build filters and
preamplifiers, you can hook up
single banded front ends directly to the Basic RX inputs. These filters
and preamps do not have
to be super but do need to do some selection, filtering and
amplification for your work. Then
you can directly digitize and DDC the RF. I do not view this as a thing
you would want to try
with the USRP "directly" hooked to the antenna.