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[Discuss-gnuradio] Re: Is there a reason why this wouldn't shift the sig

From: Jonathan Coveney
Subject: [Discuss-gnuradio] Re: Is there a reason why this wouldn't shift the signal that is demodulated?
Date: Sat, 8 Aug 2009 17:17:13 -0400

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

        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 <address@hidden>
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.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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