I also tried implementing the same idea thusly
fir_chan_coeffs = gr.firdes.low_pass (1.0, # gain
usrp_rate, # sampling rate
80e3, # low pass
cutoff freq
5.5e3, # width of
trans. band
gr.firdes.WIN_HANN) # filter type
fir_filter = gr.freq_xlating_fir_filter_ccf (1,
#decimation rate
fir_chan_coeffs, #taps
-.8e3,
#frequency translation
usrp_rate)
self.connect (self.u, gr.throttle(gr.sizeof_gr_complex, usrp_rate),
fir_filter, self.guts, self.volume_control, audio_sink)
to no avail
2009/8/8 Jonathan Coveney <[email protected]>
> My goal is to be able to read a frequency other than the frequency that was
> tuned to draw samples using usrp_rcv_cfile (ie I used 93.3M, and want to be
> able to demodulate 92.5M...I'd try to use lessons learned from wfm_rcv2 but
> that uses set_rx_freq in the pipelines, which obviously I don't have access
> to)
>
> Taking a cue from this
> http://www.nabble.com/Frequency-Hopping-td20538730.html
> I tried to shift by -.8Mhz
>
> mix_freq = -.8e6
> Cosine = gr.sig_source_f(usrp_rate,gr.GR_COS_WAVE,mix_freq,1,0)
> Sin = gr.sig_source_f(usrp_rate,gr.GR_SIN_WAVE,mix_freq,1,0)
>
> self.expjw = gr.float_to_complex()
> self.connect(Cosine,(self.expjw,0))
> self.connect(Sin,(self.expjw,1))
>
> self.mixer = gr.multiply_cc()
>
> self.connect (self.u, (self.mixer, 0))
> self.connect (self.expjw, (self.mixer, 1))
>
> self.connect (self.mixer, gr.throttle(gr.sizeof_gr_complex,
> usrp_rate), chan_filt, self.guts, self.volume_control, audio_sink)
>
> I also tried using freq_xlating_fir_filter_ccf (which googling looked like
> it was overkill) to no effect. In both cases I just hear a noisy version of
> 93.3M, I can't get it to focus on something that wasn't the center of the
> frequency that my samples were taken.
>
> Any ideas?
>
>
>
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