On Sat, Nov 30, 2013 at 2:50 AM, Kevin Reid <kpr...@switchb.org> wrote: > > This seems like a bug, but I want to check first that I'm not having > unreasonable expectations. I'm using GNU Radio 3.7.2. > > If the amplitude of the input to quadrature_demod_cf is less than about > 10^(-2.23), then the output samples are zero instead of the demodulated > signal. > > Since such an exponent is well within the range for (complex) single-float > samples, this seems like a problem with the arithmetic used by > quadrature_demod. > > I noticed it because my analog FM receiver would produce complete silence > instead of static, despite not having any squelch enabled; unfortunately, it > also produces silence on weak signals that would otherwise be intelligible. I > have a notion that this did not occur in older GNU Radio versions (e.g. 3.6) > but I'm not in a good position to test exactly where the problem might have > been introduced. > > I've attached a GRC flowgraph for experimenting with the behavior, and a > screenshot of what the demodulated output looks like just at the threshold of > failure (the signal is 200 samples per cycle). > >
I tried your grc file and the scope sink shows a perfect sinewave here. So maybe it is a voilk issue or the gr::fast_atan2f on your parchitecture. Mine was using avx_64_mmx_orc Alex _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
