Jeff Brower wrote:
I think the OP is confused at what "signal processing" is happening on the RF
daughterboard. Although some recent posts have said "none", there actually is
some
-- filters to separate the I and Q signals which were summed at the point of
original
transmission to make a single airwave.
I disagree with this; it depends on which daughterboards you're talking
about. The BasicRX and LFRX daughterboards are I/Q agnostic - the "I"
path and the "Q" path are identical. They do contain hardware* to
convert single ended signals to differential signals for USRP, and
handle biasing. But they don't care which signal is I and which signal
is Q. In fact, the two signals could be completely unrelated (as far as
the daughterboard cares). It's only the USRP that needs to know if the
signals are I and Q or unrelated signals.
* LFRX uses the AD8132, and the BasicRX uses the ADT1 transformer.
The daughterboards with tuners obviously do push I and Q down to the
USRP, and I presume do something different to each. I don't have any
such daughterboards, so I can't say specifically what each does.
This is why the two ADCs are actually sampling separate, different signals, even
though their sampling rate clocks are synchronized.
Generally, yes, the ADCs are sampling separate, downconverted to IF
signals (I and Q).
-Roshan
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