I know you say not to use a throttle, but for some reason it absolutely does not work without one. Any idea why that would be? It sounds very distorted and sped up, and then I get a bunch of xO errors. With throttling it works perfectly.
2009/8/9 Eric Blossom <[email protected]> > On Sat, Aug 08, 2009 at 05:02:55PM -0400, Jonathan Coveney wrote: > > 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) > > Consider using gr.sig_source_c. It generates a complex sinusoid. > > > > 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. > > gr.freq_xlating_fir_filter_ccf is the easiest way to extract one or > more frequency bands from a wider band input. usrp_wfm_rcv_sca.py > uses it to extract the SCA channel. > > If all you want to do is shift a frequency use gr.sig_source_c and a > gr.multiply_cc > > In virtual all cases you do _not_ want to be using throttle... > > Eric >
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