Matt Ettus wrote: >>>I would try this with the regular (non-PLL) FM demod. I think the >>>rolloff of the PLL tracking loop is what is giving you the lower gain. >>> >> >>Yes, that seems to be the problem. >>For now I switched to using the non-PLL FM-demod. >> >>Do you know if/how I can make a PLL which does not have this high roll-of. >>I played with the pll-parameters but that doesn't seem to help. >>It is critically damped, so that is probably the best we can get with this >>pll. >>Would I need another type of pll with a higher order loop-filter or something >>like that. >> > > > > I think it's just a question of bandwidth. Have you confirmed that the > PLL has at least 60 kHz of bandwidth? Bandwidth should be 200 kHz.
But when I look at the FFT of the output I see about 10 dB/octave roll-of for the pll_demod. The quadrature_demod has a straight freq response (as expected) See testcode below: I wrote a small loopback test fm_mod ->fm-demod http://www.olifantasia.com/pub/projects/gnuradio/mdvh/testcode/wfm_loopback_test.py The main code is: #mod max_dev=75e3 mod_gain = 2 * math.pi * max_dev / self.sample_rate self.fm_mod = gr.frequency_modulator_fc (mod_gain) #demod pll bandwidth = 200e3 alpha = 0.25*bandwidth * math.pi / self.sample_rate beta = alpha * alpha / 4.0 max_freq = 2.0*math.pi*100e3/self.sample_rate self.fm_demod_pll = gr.pll_freqdet_cf (alpha,beta,max_freq,-max_freq) #demod quadrature fm_demod_gain = 1.0/mod_gain self.fm_demod_quadrature = gr.quadrature_demod_cf (fm_demod_gain) When I look at the FFT of the output I see about 10 dB/octave roll-of for the pll_demod. http://www.olifantasia.com/pub/projects/gnuradio/mdvh/testcode/wfm_loopback_screenshot.gif Should this be right? The quadrature_demod has a straight freq response (as expected) Martin > > Matt > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
