Re: [Discuss-gnuradio] Question on gr.wavfile_source

[Martin Braun]

On Tue, Jun 23, 2009 at 04:49:10PM -0700, Brook Lin wrote:
> I'm trying to transmit a wave file using gr.wavfile_source(). To test my
> transmission path, I first transmit a sine wave, and I can receive it and
> sink it to sound card fine. I can hear the sound at the receiver side.
> However, if I change the source using gr.wavfile_source(), I can hear
> nothing at the receiver side but noise. Here is the my tx_path below.
> 
> =======================================================
>         dac_rate = 128e6 
>         usrp_interp = 500
>         self.u = usrp.sink_c (0, usrp_interp)
>         self.u.set_interp_rate(usrp_interp)
>         usrp_rate = dac_rate / usrp_interp           # 256 kS/s
> 
>         #src = gr.sig_source_f (32e3, gr.GR_SIN_WAVE, 440, 1)  #--I can hear
> it at the receiver side
>         src = gr.wavfile_source('test.wav', False) #--nothing can be heard
> at the receiver side
> 
>         interp_taps = optfir.low_pass (8,           # gain
>                                             usrp_rate,   # sampling rate
>                                             8e3,        # passband cutoff
> 8e3
>                                             12e3,       # stopband cutoff
> 12e3
>                                             1.0,         # passband ripple
>                                             60)          # stopband
> attenuation
>         print 'len(interp_taps)',len(interp_taps)
>         self.interpolator = gr.interp_fir_filter_fff (8, interp_taps)
>         gain = gr.multiply_const_ff(200)

I can't spot an exact problem, but two things do come to mind:
1) Your gain is awfully low, you're hardly using the dynamic range of
the ADC. Try something like 20000.
2) Use an analog modulation, such as AM (w/ carrier) or FM.

MB

-- 
Dipl.-Ing. Martin Braun           Phone: +49-(0)721-608 3790
Institut fuer Nachrichtentechnik  Fax:   +49-(0)721-608 6071
Universitaet Karlsruhe (TH)       http://www.int.uni-karlsruhe.de/

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