noiseblanker.c

/* noiseblanker.c

This file is part of a program that implements a Software-Defined Radio.

Copyright (C) 2004, 2005, 2006 by Frank Brickle, AB2KT and Bob McGwier, N4HY

This program 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 of the License, or
(at your option) any later version.

This program 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 this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

The authors can be reached by email at

ab2kt@arrl.net
or
rwmcgwier@comcast.net

or by paper mail at

The DTTS Microwave Society
6 Kathleen Place
Bridgewater, NJ 08807
*/

#include <common.h>

NB
new_noiseblanker(CXB sigbuf, REAL threshold)
{
    NB nb = (NB)safealloc(1, sizeof(nbstate), "new nbstate");
    nb->sigbuf = sigbuf;
    nb->threshold = threshold;
    nb->average_mag = 1.0;
    nb->hangtime = 0;
    nb->sigindex = 0;
    nb->delayindex = 2;
    memset(nb->delay, 0, 8 * sizeof(COMPLEX));
    return (nb);
}

void
del_nb(NB nb)
{
    if(nb)
    {
        safefree((char *)nb);
    }
}

void
noiseblanker(NB nb)
{
    int i;
    for (i = 0; i < CXBsize(nb->sigbuf); i++)
    {
        REAL cmag = Cmag(CXBdata(nb->sigbuf, i));
        nb->delay[nb->sigindex] = CXBdata(nb->sigbuf, i);
        nb->average_mag = (REAL)(0.999 * (nb->average_mag) + 0.001 * cmag);
        if((nb->hangtime == 0) && (cmag > (nb->threshold * nb->average_mag))) nb->hangtime = 7;
        if(nb->hangtime > 0)
        {
            CXBdata(nb->sigbuf, i) = Cmplx(0.0, 0.0);
            nb->hangtime--;
        } else CXBdata(nb->sigbuf, i) = nb->delay[nb->delayindex];
        nb->sigindex = (nb->sigindex + 7) & 7;
        nb->delayindex = (nb->delayindex + 7) & 7;
    }
}

void
SDROMnoiseblanker(NB nb)
{
    int i;
    for (i = 0; i < CXBsize(nb->sigbuf); i++)
    {
        REAL cmag = Cmag(CXBdata(nb->sigbuf, i));
        nb->average_sig = Cadd(Cscl(nb->average_sig, 0.75),
                               Cscl(CXBdata(nb->sigbuf, i), 0.25));
        nb->average_mag = (REAL)(0.999 * (nb->average_mag) + 0.001 * cmag);
        if(cmag > (nb->threshold * nb->average_mag)) CXBdata(nb->sigbuf, i) = nb->average_sig;
    }
}