Ian- > Ok, that makes sense. Looking back at this site > (http://www.nd.edu/~jnl/sdr/docs/tutorials/4.html#tth_sEc2.1) I see > that the DDC is combining the I and Q inputs to do complex > multiplication. I originally thought it was multiplying the I and Q > components separately, so that no input to Q would mean zero output > for Q also.
The schematic for the BasicRX daughterboard (lfrx.pdf) shows the board is *not* bringing out I and Q data separately. There are two possible antenna inputs, brought to Vin-A and Vin-B. I and Q data is generated in the USRP board logic by complex multiply less than 30 MHz. I haven't verified in the logic yet, but the results should be either one set of I-Q data (for one antenna) or two sets (if both RF inputs are used). -Jeff > -Ian Larsen > > On 7/18/07, Johnathan Corgan <[EMAIL PROTECTED]> wrote: > > Ian Larsen wrote: > > > > > I assume this also true for the BasicRX daughterboard? (Doesn't do > > > downconversion, but does do analog multiplication to get I and Q?) > > > > Almost. The boards don't do anything with the signal, but have separate > > I and Q inputs that go to the ADCs as is. > > > > On the FPGA, however, there are digital mixers that you can use to > > convert a center frequency down to baseband, so you get a complex I and > > Q signal out of that, even if you only supply a signal to the I input. > > That is what is actually happening when you "tune" a BasicRX or LFRX board. > > > > -- > > Johnathan Corgan > > Corgan Enterprises LLC > > http://corganenterprises.com _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
