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// amdemod.cpp: implementation of the CAmDemod class.
//
// This class takes I/Q baseband data and performs
// AM demodulation
// History:
// 2010-09-22 Initial creation MSW
// 2011-03-27 Initial release
// 2011-08-07 Modified FIR filter initialization call
// 2013-07-28 Added single/double precision math macros
//////////////////////////////////////////////////////////////////////
//==========================================================================================
// + + + This Software is released under the "Simplified BSD License" + + +
//Copyright 2010 Moe Wheatley. All rights reserved.
//
//Redistribution and use in source and binary forms, with or without modification, are
//permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list
// of conditions and the following disclaimer in the documentation and/or other materials
// provided with the distribution.
//
//THIS SOFTWARE IS PROVIDED BY Moe Wheatley ``AS IS'' AND ANY EXPRESS OR IMPLIED
//WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
//FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Moe Wheatley OR
//CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
//CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
//SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
//ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
//NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
//ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//The views and conclusions contained in the software and documentation are those of the
//authors and should not be interpreted as representing official policies, either expressed
//or implied, of Moe Wheatley.
//==========================================================================================
#include "amdemod.h"
#include "gui/testbench.h"
#include "dsp/datatypes.h"
#include "dsp/filtercoef.h"
#include <QDebug>
#define DC_ALPHA 0.99 //ALPHA for DC removal filter ~20Hz Fcut with 15625Hz Sample Rate
/////////////////////////////////////////////////////////////////////////////////
// Construct AM demod object
/////////////////////////////////////////////////////////////////////////////////
CAmDemod::CAmDemod(TYPEREAL samplerate) : m_SampleRate(samplerate)
{
m_z1 = 0.0;
m_Fir.InitLPFilter(0, 1.0, 50.0, 10000, 10000*1.8, m_SampleRate);//initialize LP FIR filter
}
void CAmDemod::SetBandwidth(TYPEREAL Bandwidth)
{
//create a LP filter with passband the same as the main filter bandwidth for post audio filtering
m_Fir.InitLPFilter(0, 1.0, 50.0, Bandwidth, Bandwidth*1.8, m_SampleRate);//initialize LP FIR filter
}
/////////////////////////////////////////////////////////////////////////////////
// Process envelope AM demod MONO version
/////////////////////////////////////////////////////////////////////////////////
int CAmDemod::ProcessData(int InLength, TYPECPX* pInData, TYPEREAL* pOutData)
{
for(int i=0; i<InLength; i++)
{
//calculate instantaneous power magnitude of pInData which is I*I + Q*Q
TYPECPX in = pInData[i];
TYPEREAL mag = MSQRT(in.re*in.re+in.im*in.im);
//High pass filter(DC removal) with IIR filter
// H(z) = (1 - z^-1)/(1 - ALPHA*z^-1)
TYPEREAL z0 = mag + (m_z1 * DC_ALPHA);
pOutData[i] = (z0 - m_z1);
m_z1 = z0;
}
//post filter AM audio to limit high frequency noise
m_Fir.ProcessFilter(InLength, pOutData, pOutData);
return InLength;
}
/////////////////////////////////////////////////////////////////////////////////
// Process envelope AM demod STEREO version
/////////////////////////////////////////////////////////////////////////////////
int CAmDemod::ProcessData(int InLength, TYPECPX* pInData, TYPECPX* pOutData)
{
for(int i=0; i<InLength; i++)
{
//calculate instantaneous power magnitude of pInData which is I*I + Q*Q
TYPECPX in = pInData[i];
TYPEREAL mag = MSQRT(in.re*in.re+in.im*in.im);
//High pass filter(DC removal) with IIR filter
// H(z) = (1 - z^-1)/(1 - ALPHA*z^-1)
TYPEREAL z0 = mag + (m_z1 * DC_ALPHA);
pOutData[i].re = (z0 - m_z1);
pOutData[i].im = (z0 - m_z1); //make both output channels the same
m_z1 = z0;
}
//post filter AM audio to limit high frequency noise
m_Fir.ProcessFilter(InLength, pOutData, pOutData);
return InLength;
}
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