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Upper Sideband Demodulator.

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This commit is contained in:
Hexameron 2014-06-29 22:01:56 +01:00
parent f51044931b
commit f3e5881be2
3 changed files with 28 additions and 20 deletions
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39
plugins/channel/usb/usbdemod.cpp
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@ -32,19 +32,19 @@ USBDemod::USBDemod(AudioFifo* audioFifo, SampleSink* sampleSink) :
m_volume = 2.0;
m_sampleRate = 96000;
m_frequency = 0;
m_nco.setFreq(m_frequency, m_sampleRate);
m_interpolator.create(16, m_sampleRate, 5000);
m_sampleDistanceRemain = (Real)m_sampleRate / 48000.0;
m_lowpass.create(21, 48000, 5000);
m_audioBuffer.resize(512);
m_audioBufferFill = 0;
m_undersampleCount = 0;
USBFilter = new fftfilt(0.01, m_Bandwidth / 48000.0, usbFftLen);
// if (!USBFilter) segfault;
}
USBDemod::~USBDemod()
{
if (USBFilter) delete USBFilter;
}
void USBDemod::configure(MessageQueue* messageQueue, Real Bandwidth, Real volume)
@ -55,18 +55,23 @@ void USBDemod::configure(MessageQueue* messageQueue, Real Bandwidth, Real volume
void USBDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iterator end, bool positiveOnly)
{
Complex ci;
Real a, b;
Complex c;
int n_out;
cmplx *sideband;
bool consumed;
for(SampleVector::const_iterator it = begin; it < end; ++it) {
Complex c(it->real() / 32768.0, it->imag() / 32768.0);
c *= m_nco.nextIQ();
a = it->real();
b = it->imag();
it++; // TODO: Assumes 96kHz; Expect breakage.
a += it->real();
b += it->imag();
c = Complex(a / 32678.0, b / 32768.0);
consumed = false;
// could squelch audio if RTL_SDR samplerate is not being fully decimated.
if(m_interpolator.interpolate(&m_sampleDistanceRemain, c, &consumed, &ci)) {
Real demod = ci.imag() + ci.real();
demod = 32768.0 * m_lowpass.filter(demod * 0.7);
n_out = USBFilter->run(c, &sideband);
for (int i = 0; i < n_out; i++) {
Real demod = (sideband[i].real() + sideband[i].imag()) * 0.7 * 32768.0;
// Downsample by 4x for audio display
if (!(m_undersampleCount++ & 3))
@ -80,7 +85,7 @@ void USBDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iter
uint res = m_audioFifo->write((const quint8*)&m_audioBuffer[0], m_audioBufferFill, 1);
m_audioBufferFill = 0;
}
m_sampleDistanceRemain += (Real)m_sampleRate / 48000.0;
m_sampleDistanceRemain += 2; // 96k in / 48k out
}
}
if(m_audioFifo->write((const quint8*)&m_audioBuffer[0], m_audioBufferFill, 0) != m_audioBufferFill)
@ -104,18 +109,14 @@ bool USBDemod::handleMessage(Message* cmd)
{
if(DSPSignalNotification::match(cmd)) {
DSPSignalNotification* signal = (DSPSignalNotification*)cmd;
qDebug("%d samples/sec, %lld Hz offset", signal->getSampleRate(), signal->getFrequencyOffset());
m_sampleRate = signal->getSampleRate();
m_nco.setFreq(-signal->getFrequencyOffset(), m_sampleRate);
m_interpolator.create(16, m_sampleRate, m_Bandwidth);
m_sampleDistanceRemain = m_sampleRate / 48000.0;
m_sampleDistanceRemain = 0.0;
cmd->completed();
return true;
} else if(MsgConfigureUSBDemod::match(cmd)) {
MsgConfigureUSBDemod* cfg = (MsgConfigureUSBDemod*)cmd;
m_Bandwidth = cfg->getBandwidth();
m_interpolator.create(16, m_sampleRate, m_Bandwidth);
m_lowpass.create(21, 48000, cfg->getBandwidth());
USBFilter->create_filter(0.01, m_Bandwidth / 48000.0);
m_volume = cfg->getVolume();
m_volume *= m_volume * 0.1;
cmd->completed();

4
plugins/channel/usb/usbdemod.h
View File

@ -23,9 +23,12 @@
#include "dsp/nco.h"
#include "dsp/interpolator.h"
#include "dsp/lowpass.h"
#include "dsp/fftfilt.h"
#include "audio/audiofifo.h"
#include "util/message.h"
#define usbFftLen 1024
class AudioFifo;
class USBDemod : public SampleSink {
@ -84,6 +87,7 @@ private:
AudioVector m_audioBuffer;
uint m_audioBufferFill;
AudioFifo* m_audioFifo;
fftfilt* USBFilter;
SampleSink* m_sampleSink;
SampleVector m_sampleBuffer;

5
sdrbase/dsp/fftfilt.cxx
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@ -155,8 +155,11 @@ int fftfilt::run(const cmplx & in, cmplx **out)
memcpy(freqdata, timedata, flen * sizeof(cmplx));
fft->ComplexFFT(freqdata);
for (int i = 0; i < flen; i++)
// Discard negative frequencies for ssb
for (int i = 0; i < flen2; i++) {
freqdata[i] *= filter[i];
freqdata[flen2 + i] = 0;
}
fft->InverseComplexFFT(freqdata);