Re: [Discuss-gnuradio] New to gnuradio - Complex sampling question - urgent

[Eric Blossom]

On Sat, Jun 13, 2009 at 02:31:59AM +0200, Sebastiaan Heunis wrote:
> Jason
> 
> From what I've picked up, you need two external sampled signals to get
> an I-Q signal.  With the TV tuner daughterboard, you automatically get
> two signals.  You just need to set the mux accordingly.  When you use
> a BasicRX, you need to feed the same signal to both inputs and use a
> mux value of 0x32103210.

If you use the standard interfaces, you don't have to do anything. You
always get a valid complex baseband signal.

The daughterboard code knows which boards have a single real output
and which have quadrature inputs.  In the single real case (e.g.,
TVRX), the library configures the mux such that it feeds the single
input into the I side of the DDC and connects a constant zero into the
Q side.  The output of the DDC is always complex.  In the case of
daughterboards with quadrature output, one input is connected to the 
I input of the DDC and the other is connected to the Q input.

See http://gnuradio.org/trac/wiki/UsrpRfxDiagrams

Eric