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Alternate NFM demod.

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This commit is contained in:
John Greb 2014-12-22 23:12:05 +00:00
parent 4135c8f5ad
commit 917cca4543
2 changed files with 25 additions and 17 deletions
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38
plugins/channel/nfm/nfmdemod.cpp
View File

@ -29,10 +29,11 @@ NFMDemod::NFMDemod(AudioFifo* audioFifo, SampleSink* sampleSink) :
{ {
m_rfBandwidth = 12500; m_rfBandwidth = 12500;
m_volume = 2.0; m_volume = 2.0;
m_squelchLevel = pow(10.0, -40.0 / 20.0); m_squelchLevel = pow(10.0, -40.0 / 10.0);
m_sampleRate = 500000; m_sampleRate = 500000;
m_frequency = 0; m_frequency = 0;
m_squelchLevel *= m_squelchLevel; m_scale = 0;
m_framedrop = 0;
m_nco.setFreq(m_frequency, m_sampleRate); m_nco.setFreq(m_frequency, m_sampleRate);
m_interpolator.create(16, m_sampleRate, 12500); m_interpolator.create(16, m_sampleRate, 12500);
@ -56,30 +57,34 @@ void NFMDemod::configure(MessageQueue* messageQueue, Real rfBandwidth, Real afBa
cmd->submit(messageQueue, this); cmd->submit(messageQueue, this);
} }
int framedrop = 0;
void NFMDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iterator end, bool positiveOnly) void NFMDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iterator end, bool positiveOnly)
{ {
Complex ci; Complex ci;
qint16 sample; qint16 sample;
Real a, b, s, demod;
double meansqr = 1.0;
for(SampleVector::const_iterator it = begin; it < end; ++it) { for(SampleVector::const_iterator it = begin; it < end; ++it) {
Complex c(it->real() / 32768.0, it->imag() / 32768.0); Complex c(it->real() / 32768.0, it->imag() / 32768.0);
c *= m_nco.nextIQ(); c *= m_nco.nextIQ();
if(m_interpolator.interpolate(&m_sampleDistanceRemain, c, &ci)) { if(m_interpolator.interpolate(&m_sampleDistanceRemain, c, &ci)) {
if (++framedrop & 1) { s = ci.real() * ci.real() + ci.imag() * ci.imag();
m_movingAverage.feed(ci.real() * ci.real() + ci.imag() * ci.imag()); meansqr += s;
if(m_movingAverage.average() >= m_squelchLevel) m_movingAverage.feed(s);
m_squelchState = m_sampleRate / 50; if(m_movingAverage.average() >= m_squelchLevel)
} m_squelchState = m_sampleRate / 50;
Complex d = ci * conj(m_lastSample);
m_lastSample = ci; a = m_scale * m_this.real() * (m_last.imag() - ci.imag());
Real demod = atan2(d.imag(), d.real()) / M_PI; b = m_scale * m_this.imag() * (m_last.real() - ci.real());
demod = m_volume * m_lowpass.filter(demod); m_last = m_this;
sample = demod * 32767; m_this = Complex(ci.real(), ci.imag());
demod = m_volume * m_lowpass.filter(b - a);
sample = demod * 30000;
// Display audio spectrum to 12kHz // Display audio spectrum to 12kHz
if (!(framedrop & 1)) if (!(m_framedrop & 1))
m_sampleBuffer.push_back(Sample(sample, sample)); m_sampleBuffer.push_back(Sample(sample, sample));
if(m_squelchState > 0) if(m_squelchState > 0)
@ -108,6 +113,8 @@ void NFMDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iter
if(m_sampleSink != NULL) if(m_sampleSink != NULL)
m_sampleSink->feed(m_sampleBuffer.begin(), m_sampleBuffer.end(), true); m_sampleSink->feed(m_sampleBuffer.begin(), m_sampleBuffer.end(), true);
m_sampleBuffer.clear(); m_sampleBuffer.clear();
m_scale = 0.8 * m_scale + 0.2 * ( end - begin) * m_sampleRate / 48000 / meansqr;
} }
void NFMDemod::start() void NFMDemod::start()
@ -136,8 +143,7 @@ bool NFMDemod::handleMessage(Message* cmd)
m_rfBandwidth = cfg->getRFBandwidth(); m_rfBandwidth = cfg->getRFBandwidth();
m_interpolator.create(16, m_sampleRate, m_rfBandwidth / 2.1); m_interpolator.create(16, m_sampleRate, m_rfBandwidth / 2.1);
m_lowpass.create(21, 48000, cfg->getAFBandwidth()); m_lowpass.create(21, 48000, cfg->getAFBandwidth());
m_squelchLevel = pow(10.0, cfg->getSquelch() / 20.0); m_squelchLevel = pow(10.0, cfg->getSquelch() / 10.0);
m_squelchLevel *= m_squelchLevel;
m_volume = cfg->getVolume(); m_volume = cfg->getVolume();
cmd->completed(); cmd->completed();
return true; return true;

4
plugins/channel/nfm/nfmdemod.h
View File

@ -89,8 +89,10 @@ private:
Lowpass<Real> m_lowpass; Lowpass<Real> m_lowpass;
int m_squelchState; int m_squelchState;
int m_framedrop;
Complex m_lastSample; double m_scale;
Complex m_last, m_this;
MovingAverage m_movingAverage; MovingAverage m_movingAverage;
AudioVector m_audioBuffer; AudioVector m_audioBuffer;