Re: [Discuss-gnuradio] Spectrum_sense of a smaller banwidth

[Tom Rondeau]

On Tue, Mar 10, 2009 at 6:33 AM, Adi85 <address@hidden> wrote:
>
> Still getting an error!
> thank you in advance
>
> class topBlock(gr.top_block):
>>    def __init__(self):
>>        gr.top_block.__init__(self)
>>
>>        fftsize = 256
>>        udecim = 256
>>
>>        mywin = window.blackmanharris(fftsize)
>>        fft = gr.fft_vcc(fftsize, True, mywin)
>>
>>        signal = usrp.source_c(0,udecim)    # signal from Basic RX,
>> decimation=256
>>        v_sink = gr.vector_sink_c()
>>
>>        self.connect(signal, fft, v_sink)
>>
>>        # Do stuff with v_sink.data()
>>        print v_sink.data()
>>
>  if __name__ == "__main__":
>>    print "Initilizing.."
>>    tb = topBlock()
>>    print "Flowgraph start.."
>>    tb.start()
>>    print "Exiting.."
>
>
> but i get the same error:
>
> ValueError: itemsize mismatch: usrp1_source_c(2):0 using 8,
> fft_vcc_fftw(1):0 using 2048
>
>
> the value 2048 depends of the fft size 2048=8*256
>
> thank you very much!


It's a slight misunderstanding of the word "vector." The FFT outputs a
vector of size (sizeof(datatype)*fftsize). The vector sink is really
just a sink that stuffs a stream of items into a vector object. What
it really wants to see is a stream in, not a vector in.

Simply put, add a gr.vector_to_stream between the fft block and vector
sink block.

Tom