Hi Marcus
Thanks for the explanation.It really helped me
Thanks and regards
Sandhya
On Thu, Oct 10, 2013 at 3:21 PM, Marcus Müller <mar...@hostalia.de> wrote:
> Hi Sandhya,
>
> the official documentation for the frequency xlating fir filter (
> http://gnuradio.org/doc/**doxygen/classgr_1_1filter_1_**
> 1freq__xlating__fir__filter__**ccc.html<http://gnuradio.org/doc/doxygen/classgr_1_1filter_1_1freq__xlating__fir__filter__ccc.html>)
> says:
>
> FIR filter combined with frequency translation with gr_complex input,
> gr_complex output and gr_complex taps.
>
> This class efficiently combines a frequency translation (typically "down
> conversion") with a FIR filter (typically low-pass) and decimation. It is
> ideally suited for a "channel selection filter" and can be efficiently used
> to select and decimate a narrow band signal out of wide bandwidth input.
>
> Uses a single input array to produce a single output array. Additional
> inputs and/or outputs are ignored.
>
> And that's exactly what it does: It takes coefficients of a FIR filter,
> and applies them to the signal, simultaneously shifting its frequency. As
> far as I remember, it does that by dynamically updating the taps by
> multiplying them with a complex sinusoid of the negative desired shift
> frequency. These taps are then applied to the signal, before that get's
> shifted by the shift frequency. There is a discussion going on on the sign
> of the exponent, so look for Achilleas recent posts with the title "Bug in
> freq_xlating_fir_filter_XXX".
> However, best explanation is probably the source code, if you're not
> content with the documentation. Enhancing documentation is always welcome!
> See gr-filter/lib/freq_xlating_**fir_filter_XXX_impl.cc.t and
> gr-filter/lib/freq_xlating_**fir_filter_XXX_impl.h.t; nothing overly
> complex.
>
> Regarding to WBFM receive: You're right, documentation is sparse here.
> Strangely, the class itself (analog.wfm_rcv_pll) does not even show up in
> the current sphinx documentation. So there's only the sources left to
> consult:
> gr-analog/python/analog/wfm_**rcv_pll.py. Luckily, there's a lot of
> comments in the code, so maybe that will help you understand what's going
> on internally (so what really making that thing decode stereo radio ;) ).
>
> Hope I was a bit helpful today,
> Marcus
>
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