db_width.m

gnuradio软件无线电源程序.现在的手机多基于软件无线电

#
# Copyright 2001 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.
# 
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING.  If not, write to
# the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
# Boston, MA 02111-1307, USA.

## find the N-dB width of the given filter
## E.g., to find the 3-dB width, use width = db_width (taps, -3.0)
## the result is normalized to nyquist == 1

function width = db_width (taps, db)
  [H,w] = freqz (taps, 1, 4096);
  Habs = abs(H);
  max_H = max(Habs);
  min_H = min(Habs);
  threshold = max_H * 10^(db/20);
  if (min_H > threshold)
    error ("The %g dB point is never reached", db);
  endif
  above = Habs >= threshold;
  width = sum(above) / length (above);
endfunction