On 8/30/07, Ismail Mohamed <[EMAIL PROTECTED]> wrote: > Hi again, > > Recently there has been talk about the I and Q components of the > signal. I understand the analytic signal concept, also the > implementation as shown on: > > http://gnuradio.org/trac/wiki/UsrpRfxDiagrams > > where it says, > > "Right idea, except that there is effectively a single complex > multipler. I.e., I2+jQ2 = (I1+jQ1) * exp(jwt)." > > So the analytic signal is generated on the motherboard and mixed up to a > higher carrier on the daughterboard, i.e. to a new 'w' but same I and Q. > > My question is that, with the LFTX and LFRX, if I tune the daughterboard > to DC, this would make w=0. So there would be no carrier. How are the > I and Q components separated? Or is it simply that each alternate > sample is I and Q, and in essence we are sending a purely real signal, > but saying each second sample represents the imaginary?
>From my limited DSP understanding, at baseband, I and Q are simply phase relationships and amplitude information around and within the unit circle. With that being said, I don't think I and Q can be combined into a single real signal while preserving information simply because DC has no phase component. On the other hand, if the LF cards have both I and Q inputs/outputs, then you should be able to see essentially two signals come out and maintain their proper information. If it's only real - you'll probably have to mix up to some IF to maintain all information. I believe the real question here is if you can do complex sampling on a real signal centered strictly around DC - which I don't think you can. Anyone wish to comment? I am most likely wrong, but I'd definitely like to know the real answer to this as well. Brian _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
