Eric- > > > The LFRX has two separate antenna inputs, supplied to Vin-A and > > > Vin-B. These are not I-Q data. USRP board FPGA logic would apply > > > one mixer or two (30 MHz or less). > > > > [...] > > > > > The RFX2400 mixes with a 2.4 GHz osc and creates one set of I-Q 65 > > > MHz range signals, +/-I on Vin-A and +/-Q on Vin-B. To get baseband > > > signals, the logic has to apply two mixers. > > > > The FPGA DDC logic uses a single but *complex* mixer to do frequency > > conversion of the signal from the ADCs. That is, it treats the data > > from Vin-A and Vin-B as a complex number in I and Q format, and > > multiplies this complex number by a complex sinusoid of a configurable > > frequency. This is very different from having two mixers. > > In fact the routing from the ADCs to the inputs of the DDCs is > controlled by the input mux in the FPGA. You can route any ADC > into any DDC input, or you can stick a constant zero into the Q input > (details below). > > The _default_ wiring depends on the software that controls the given > daughterboard. By default the Basic Rx and LF RX daughterboard code > treats the two inputs as two separate real inputs (not I & Q), one > into DDC 0, one into DDC 1. You can easily override this by calling > u.set_mux(...) The RFX-* daughterboards treat the signals as I & Q, > since that's the only configuration that makes sense given the > quadrature output of the RFX-* boards.
Thanks, that's very helpful. I thought there would have to be a way to form real-valued data for the low-end daughtercards, but hadn't found it yet. -Jeff > See http://gnuradio.org/trac/wiki/UsrpRfxDiagrams > > /*! > * \brief Set input mux configuration. > * > * This determines which ADC (or constant zero) is connected to > * each DDC input. There are 4 DDCs. Each has two inputs. > * > * <pre> > * Mux value: > * > * 3 2 1 > * 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 > * +-------+-------+-------+-------+-------+-------+-------+-------+ > * | Q3 | I3 | Q2 | I2 | Q1 | I1 | Q0 | I0 | > * +-------+-------+-------+-------+-------+-------+-------+-------+ > * > * Each 4-bit I field is either 0,1,2,3 > * Each 4-bit Q field is either 0,1,2,3 or 0xf (input is const zero) > * All Q's must be 0xf or none of them may be 0xf > * </pre> > */ > bool set_mux (int mux); > > Eric [ decloaking after vacation ;) ] _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
