schrieb Bernardo Gonçalves am 2011-01-25 10:15: > Hello everyone, > > As Euripedes Rocha told few days ago in the email "Who actually *does* > use GNU Radio?", we're starting to use it here, but we do not currently > have daughterboards to use with USRP2. > > Due to this, specially in my case, I'm building some simple diagrams > using GRC, and one of them is a FM stereo transmitter/receiver in the > same flow graph. > > Basically, the problem is that it works just as mono, not stereo... > > Here is a screenshot of the flow graph: > http://dl.dropbox.com/u/8898915/fmstereotxrx.png > > The grc's file is here: > http://dl.dropbox.com/u/8898915/FMstereotxrx.grc
First, I like this very much. It's a nice example of how easy it is to implement a system like FM mod/demod in GRC. Did you consider donating this to GNU Radio as a GRC example? I did something similar, just needs the proper docs. Second, I looked at your flowgraph. You shift the difference part from center frequency 38kHz to 0 with the Xlating FIR filter, and then use a complex-to-float block. This will not result in the positive frequencies. You'd rather have to filter out the negative frequencies with a Hilbert transformer, that is a special FIR filter keeping only positive frequencies, before converting to float again. A different way would be to do it analogue to analog (;-)): first bandpass filtering for 38kHz+-15Khz, mixing down with 38kHz to 0 and filtering out the mirror image > 38kHz. The first one should be working much better in a digital complex-valued system. A sample file for testing the graph would be very helpful, with distinguishable left-right channels. Patrick -- Engineers motto: cheap, good, fast: choose any two Patrick Strasser <patrick dot strasser at student dot tugraz dot at> Student of Telemati_cs_, Techn. University Graz, Austria _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
