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102 lines
3.0 KiB
Java
102 lines
3.0 KiB
Java
/*******************************************************************************
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* SDR Trunk
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* Copyright (C) 2014 Dennis Sheirer
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>
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******************************************************************************/
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package dsp.nbfm;
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import sample.Listener;
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import sample.complex.ComplexSample;
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import sample.real.RealSampleListener;
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public class FMDiscriminator implements Listener<ComplexSample>
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{
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private RealSampleListener mListener;
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private ComplexSample mPreviousSample = new ComplexSample( 0.0f, 0.0f );
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private double mGain;
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/**
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* Implements a polar discriminator with ArcTangent angle estimator to
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* demodulate complex sampled frequency modulated signals.
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*
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* @param gain - gain to be applied to the demodulated output - can be
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* dynamically applied to continuously adjust audio output
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*/
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public FMDiscriminator( double gain )
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{
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mGain = gain;
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}
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public void dispose()
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{
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mListener = null;
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mPreviousSample = null;
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}
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public synchronized void setGain( double gain )
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{
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mGain = gain;
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}
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@Override
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public void receive( ComplexSample currentSample )
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{
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/**
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* Multiply the current sample against the complex conjugate of the
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* previous sample to derive the phase delta between the two samples
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*
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* Negating the previous sample quadrature produces the conjugate
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*/
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double i = ( currentSample.inphase() * mPreviousSample.inphase() ) -
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( currentSample.quadrature() * -mPreviousSample.quadrature() );
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double q = ( currentSample.quadrature() * mPreviousSample.inphase() ) +
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( currentSample.inphase() * -mPreviousSample.quadrature() );
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double angle;
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//Check for divide by zero
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if( i == 0 )
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{
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angle = 0.0;
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}
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else
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{
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/**
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* Use the arcus tangent of imaginary (q) divided by real (i) to
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* get the phase angle (+/-) which was directly manipulated by the
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* original message waveform during the modulation. This value now
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* serves as the instantaneous amplitude of the demodulated signal
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*/
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double denominator = 1.0d / i;
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angle = Math.atan( (double)q * denominator );
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}
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if( mListener != null )
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{
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mListener.receive( (float)( angle * mGain ) );
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}
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/**
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* Store the current sample to use during the next iteration
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*/
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mPreviousSample = currentSample;
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}
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public void setListener( RealSampleListener listener )
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{
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mListener = listener;
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}
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}
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