Re: [Discuss-gnuradio] gr_firdes_bandpass()

[Eric Blossom]

On Wed, May 13, 2009 at 03:40:31PM -0400, Marcus D. Leech wrote:
> I don't understand why this is failing:
> 
> Traceback (most recent call last):
>   File "./top_block.py", line 184, in <module>
>     tb = top_block(options)
>   File "./top_block.py", line 97, in __init__
>     1, bw, -7.0, 7.0, 150, firdes.WIN_HAMMING, 6.76))
>   File
> "/usr/local/lib/python2.5/site-packages/gnuradio/gr/gnuradio_swig_py_general.py",
> line 2729, in band_pass
>     return _gnuradio_swig_py_general.firdes_band_pass(*args, **kwargs)
> IndexError: gr_firdes check failed: 0 < fa <= sampling_freq / 2
> 
> 
> When I specify negative frequencies, it does this.
> 
> I thought that with a complex filter, I could specify negative frequency?
> 
> This particular filter is a decimating filter that is decminating from
> 500KHz sample rate down to 32KHz sample rate,
>   with cutoff between -7KHz and +7KHz.   But I'm triggering this error,
> and I don't understand why.  This is from
>   a GRC flow-graph.
> 

Just use a low pass (0 .. 7k). No need for the bandpass.
firdes_band_pass (and the lowpass for that matter) design real filters
coeffs that you can use with gr.fir_filter_ccf.

Eric