Re: [Discuss-gnuradio] pll refout vs carriertracking

[Matt Ettus]

Bob --

I think we have a problem with carriertracking -- it was supposed to mix 
the input signal down, and output that, but it looks like it just 
outputs the reference, like refout.

Charles --
To detect AM, you can:

1 - take output of pll_refout_cc, take its complex conjugate and complex 
multiply that by the input signal.  The audio you want is in the real 
output.  The imaginary output should only have noise.  If the RMS value 
of both is about the same you don't have lock, or the signal is very noisy.

-OR-

2 - Fix pll_carriertracking_cc to do what I said in 1, above, since that 
is what it was supposed to do.

Matt

Robert McGwier wrote:

> You are correct.  pll_carriertracking_cc returns the recovered 
> carrier.  Sending to baseband is then done by a complex multiply 
> block, don't forget the conjugation.
>
>
> Bob
>
>
> Charles Swiger wrote:
>
> > All - Do I understand correctly that gr.pll_carriertracking_cc() is
> > supposed to downconvert to DC?  I don't see it doing that, and can't
> > see in the work functions where that magic would be accomplished.
> >
> > Just want to make sure I'm building the most efficient graph possible.
> > I tried both in an existing AM detector with a 7.5KHz IF and both work
> > just the same with an external mixer.
> >
> > ----------------------------------------------------------------
> > refout:
> >
> > int
> > gr_pll_refout_cc::work (int noutput_items,
> >                    gr_vector_const_void_star &input_items,
> >                    gr_vector_void_star &output_items)
> > {
> >   const gr_complex *iptr = (gr_complex *) input_items[0];
> >   gr_complex *optr = (gr_complex *) output_items[0];
> >
> >   float error;
> >   float t_imag, t_real;
> >   int   size = noutput_items;
> >
> >   while (size-- > 0) {
> >     error = phase_detector(*iptr++,d_phase);
> >
> >     d_freq = d_freq + d_beta * error;
> >     d_phase = mod_2pi(d_phase + d_freq + d_alpha * error);
> >
> >     if (d_freq > d_max_freq)
> >       d_freq = d_max_freq;
> >     else if (d_freq < d_min_freq)
> >       d_freq = d_min_freq;
> >     gr_sincosf(d_phase,&t_imag,&t_real);
> >     *optr++ = gr_complex(t_real,t_imag);
> >   }
> >   return noutput_items;
> > }
> >
> >
> > -----------------------------------------------------------------
> > carriertracking:
> >
> > int
> > gr_pll_carriertracking_cc::work (int noutput_items,
> >                                  gr_vector_const_void_star &input_items,
> >                                  gr_vector_void_star &output_items)
> > {
> >   const gr_complex *iptr = (gr_complex *) input_items[0];
> >   gr_complex *optr = (gr_complex *) output_items[0];
> >
> >   float error;
> >   float t_imag, t_real;
> >
> >   for (int i = 0; i < noutput_items; i++){
> >     error = phase_detector(iptr[i],d_phase);
> >
> >     d_freq = d_freq + d_beta * error;
> >     d_phase = mod_2pi(d_phase + d_freq + d_alpha * error);
> >
> >     if (d_freq > d_max_freq)
> >       d_freq = d_max_freq;
> >     else if (d_freq < d_min_freq)
> >       d_freq = d_min_freq;
> >     gr_sincosf(d_phase,&t_imag,&t_real);
> >     optr[i] = gr_complex(t_real,t_imag);
> >     d_locksig = d_locksig * (1.0 - d_alpha) + d_alpha*(iptr[i].real() *
> > t_real + iptr[i].imag() * t_imag);
> >
> >     if ((d_squelch_enable) && !lock_detector())
> >       optr[i] = 0;
> >   }
> >   return noutput_items;
> > }
> >
> >
> >
> >
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> >
> >