On Tue, May 20, 2008 at 8:52 PM, Charles Swiger <[EMAIL PROTECTED]> wrote: > After converting atsc_fpll to handle complex input (to eliminate one > upconverter) it almost works, only the video out has problems. > > The problem starts when this: > > float I = input.real() * a_sin; > float Q = input.real() * a_cos; > > is changed to this: > > gr_complex IQ = input * gr_complex(a_cos,-a_sin); > > which would be necessary to handle negative frequencies I think. > Everything else checks out ok, I even tried using gr_sincos.h in place > of gr_nco.h like in gr_pll_carriertracking_cc and it behaves exectly the > same. > > > Working: > > gr_complex input = agc.scale(in[k]); > gr_sincosf(d_phase,&a_sin,&a_cos); > > float I = input.real() * a_sin; > float Q = input.real() * a_cos; > > out[k] = I; > gr_complex filtered_IQ = afc.filter(gr_complex(I,Q)); > float x = phase_detector(filtered_IQ,0); > static const float alpha = 0.001; > static const float beta = alpha * alpha / 4; > d_freq = d_freq + beta * x; > d_phase = mod_2pi(d_phase + d_freq + alpha * x); > > > mpeg_packet_error_rate.py: 485526 errors out of 2165316 packets. 1679790 > good packets. Error rate = 0.224 > > Almost working: > > gr_complex input = agc.scale(in[k]); > gr_sincosf(d_phase,&a_sin,&a_cos); > > gr_complex IQ = input * gr_complex(a_cos,-a_sin); > > out[k] = IQ.real(); > gr_complex filtered_IQ = afc.filter(gr_complex(I,Q)); > float x = phase_detector(filtered_IQ,0); > static const float alpha = 0.001; > static const float beta = alpha * alpha / 4; > d_freq = d_freq + beta * x; > d_phase = mod_2pi(d_phase + d_freq + alpha * x); > > mpeg_packet_error_rate.py: 258539 errors out of 2165280 packets. 1906741 > good packets. Error rate = 0.119 > > Looks like a 36 missing packets, even tho the error rate is less, as the > video is certainly worse in mplayer. > > --Chuck
I don't know much about 8-VSB, but I was under the impression that it's a single sideband modulation scheme that benefits from being real only to avoid all the complex math associated with other modulation schemes. Do you know if this is true? I suppose I am just a little ignorant on the subject and looking to be enlightened. Thanks in advance. Brian _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
