Listing 2. Quadrature Demodulator Implementation

/*
 * Copyright 2004 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio is free software; you can redistribute
 * it and/or modify it under the terms of the GNU
 * General Public License as published by the Free
 * Software Foundation; either version 2, or (at
 * your option) any later version.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <gr_quadrature_demod_cf.h>
#include <gr_io_signature.h>

gr_quadrature_demod_cf::gr_quadrature_demod_cf (
                                         float gain)
  : gr_sync_block (
       "quadrature_demod_cf",
      gr_make_io_signature(1,1,sizeof (gr_complex)),
      gr_make_io_signature(1,1,sizeof (float))),
    d_gain (gain)
{
  set_history (2);    // provide 1 sample look ahead
}

gr_quadrature_demod_cf_sptr
gr_make_quadrature_demod_cf (float gain)
{
  return gr_quadrature_demod_cf_sptr (
      new gr_quadrature_demod_cf (gain));
}

int
gr_quadrature_demod_cf::sync_work (
    int noutput_items,
    gr_vector_const_void_star &input_items,
    gr_vector_void_star &output_items)
{
  gr_complex *in = (gr_complex *) input_items[0];
  float *out = (float *) output_items[0];
  in++;         // ensure that in[-1] is valid

  for (int i = 0; i < noutput_items; i++){
    gr_complex product = in[i] * conj (in[i-1]);
    out[i] = d_gain * arg (product);
  }

  return noutput_items;
}