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NFM demod: adjust phase discriminator settings. Put in in a separate header

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This commit is contained in:
Edouard Griffiths 2015-12-16 21:12:12 +01:00
parent 5ca9004167
commit 28bde131ba
4 changed files with 57 additions and 33 deletions
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1
CMakeLists.txt
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@ -167,6 +167,7 @@ set(sdrbase_HEADERS
include/dsp/misc.h
include/dsp/movingaverage.h
include/dsp/nco.h
include/dsp/phasediscri.hpp
include/dsp/phaselock.h
sdrbase/dsp/pidcontroller.h
include/dsp/samplefifo.h

50
include/dsp/phasediscri.hpp Normal file
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@ -0,0 +1,50 @@
///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2015 F4EXB //
// written by Edouard Griffiths //
// //
// 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 as version 3 of the License, or //
// //
// 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 V3 for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program. If not, see <http://www.gnu.org/licenses/>. //
///////////////////////////////////////////////////////////////////////////////////
#ifndef INCLUDE_DSP_PHASEDISCRI_H_
#define INCLUDE_DSP_PHASEDISCRI_H_
/**
* Standard discriminator using atan2. On modern processors this is as efficient as the non atan2 one.
* This is better for high fidelity.
*/
Real phaseDiscriminator(const Complex& sample)
{
Complex d(std::conj(m_m1Sample) * sample);
m_m1Sample = sample;
return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
}
/**
* Alternative without atan at the expense of a slight distorsion on very wideband signals
* http://www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
* in addition it needs scaling by instantaneous magnitude squared and volume (0..10) adjustment factor
*/
Real phaseDiscriminator2(const Complex& sample)
{
Real ip = sample.real() - m_m2Sample.real();
Real qp = sample.imag() - m_m2Sample.imag();
Real h1 = m_m1Sample.real() * qp;
Real h2 = m_m1Sample.imag() * ip;
m_m2Sample = m_m1Sample;
m_m1Sample = sample;
return ((h1 - h2) / M_PI) * m_fmScaling;
}
#endif /* INCLUDE_DSP_PHASEDISCRI_H_ */

8
plugins/channel/nfm/nfmdemod.cpp
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@ -38,8 +38,8 @@ NFMDemod::NFMDemod() :
m_audioMute(false),
m_afSquelch(2, afSqTones),
m_audioFifo(4, 48000),
m_fmExcursion(4800),
m_fmScaling(384000/4800),
m_fmExcursion(2400),
m_fmScaling(384000/2400),
m_settingsMutex(QMutex::Recursive)
{
setObjectName("NFMDemod");
@ -141,7 +141,7 @@ void NFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
m_AGC.feed(ci);
Real demod = phaseDiscriminator2(ci, 0.5);
Real demod = phaseDiscriminator2(ci);
m_m2Sample = m_m1Sample;
m_m1Sample = ci;
@ -341,7 +341,7 @@ void NFMDemod::apply()
m_settingsMutex.lock();
m_lowpass.create(301, m_config.m_audioSampleRate, 250.0);
m_bandpass.create(301, m_config.m_audioSampleRate, 300.0, m_config.m_afBandwidth);
m_fmExcursion = m_config.m_afBandwidth;
m_fmExcursion = m_config.m_afBandwidth / 2.0f;
m_fmScaling = m_config.m_inputSampleRate / m_fmExcursion;
m_settingsMutex.unlock();
}

29
plugins/channel/nfm/nfmdemod.h
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@ -188,34 +188,7 @@ private:
NFMDemodGUI *m_nfmDemodGUI;
QMutex m_settingsMutex;
/**
* Standard discriminator using atan2. On modern processors this is as efficient as the non atan2 one.
* This is better for high fidelity.
*/
Real phaseDiscriminator(const Complex& sample)
{
Complex d(std::conj(m_m1Sample) * sample);
m_m1Sample = sample;
return (std::atan2(d.imag(), d.real()) / M_PI_2) * m_fmScaling;
}
/**
* Alternative without atan at the expense of a slight distorsion on very wideband signals
* http://www.embedded.com/design/configurable-systems/4212086/DSP-Tricks--Frequency-demodulation-algorithms-
* in addition it needs scaling by instantaneous magnitude squared and volume (0..10) adjustment factor
*/
Real phaseDiscriminator2(const Complex& sample, Real msq)
{
Real ip = sample.real() - m_m2Sample.real();
Real qp = sample.imag() - m_m2Sample.imag();
Real h1 = m_m1Sample.real() * qp;
Real h2 = m_m1Sample.imag() * ip;
m_m2Sample = m_m1Sample;
m_m1Sample = sample;
return ((h1 - h2) / (msq * M_PI)) * m_fmScaling;
}
#include "dsp/phasediscri.hpp"
void apply();
};