[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Discuss-gnuradio] quadrature_demod losing weak signals
From: |
Alexandru Csete |
Subject: |
Re: [Discuss-gnuradio] quadrature_demod losing weak signals |
Date: |
Sat, 30 Nov 2013 11:09:07 +0100 |
On Sat, Nov 30, 2013 at 2:50 AM, Kevin Reid <address@hidden> 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