Re: [Discuss-gnuradio] IndexError: gr_firdes check failed: 0 < fa <= sampling_freq / 2

[Tom Rondeau]

On Tue, Mar 12, 2013 at 5:20 PM,  <address@hidden> wrote:
> Hello everyone! I am getting another weird error here. i received my USB e4k 
> tuner and it was working. On OP25 i was using the scopes trying to figure how 
> to get the four lines of dots and with RTL_FM i was getting audio, although 
> the quality was bad. So i shut it down and i went out try on high ground but 
> the signal was still weak. So i shut it down again, put myself within line of 
> sight of the tower, and started it up and now OP25 dies like this:
>
> Traceback (most recent call last):
> File "/home/matt/gr-baz/gr-baz-master/samples/op25_grc.py", line 595, in 
> <module>
> tb = op25_grc()
> File "/home/matt/gr-baz/gr-baz-master/samples/op25_grc.py", line 339, in 
> __init__
> self.gr_freq_xlating_fir_filter_xxx_0 = gr.freq_xlating_fir_filter_ccc(decim, 
> (firdes.low_pass(1, samp_rate, xlate_bandwidth/2, 1000)), 
> xlate_offset+xlate_offset_fine-fine_click_freq-auto_tune_offset_freq, 
> samp_rate)
> File 
> "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gnuradio_core_general.py",
>  line 6871, in low_pass
> return _gnuradio_core_general.firdes_low_pass(*args, **kwargs)
> IndexError: gr_firdes check failed: 0 < fa <= sampling_freq / 2
>
> I have no idea how OP25 (same for RTL_FM) goes from working to failing with 
> this error. Anyone have any ideas about this error?
>
> Cheers,
> Matt

That error message is pretty explicit in what it's telling you. Either
xlate_bandwidth/2 is less than 0 or greater than samp_rate/2. It
should be easy enough to print out the value you are passing it to see
what you are actually passing the filter constructor algorithm.

Tom