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Inf/Sup frequency shift scheme change to set bandwidth closer to device center frequency

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This commit is contained in:
f4exb
2018-05-10 22:17:39 +02:00
parent 6a5a35285e
commit 4bb749ce65
11 changed files with 306 additions and 269 deletions
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sdrbase/dsp/devicesamplesource.cpp
+43 -17
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@@ -54,23 +54,8 @@ qint64 DeviceSampleSource::calculateDeviceCenterFrequency(
deviceCenterFrequency = deviceCenterFrequency < 0 ? 0 : deviceCenterFrequency;
qint64 f_img = deviceCenterFrequency;
if ((log2Decim == 0) || (fcPos == FC_POS_CENTER))
{
f_img = deviceCenterFrequency;
}
else
{
if (fcPos == FC_POS_INFRA)
{
deviceCenterFrequency += (devSampleRate / 4);
f_img = deviceCenterFrequency + devSampleRate/2;
}
else if (fcPos == FC_POS_SUPRA)
{
deviceCenterFrequency -= (devSampleRate / 4);
f_img = deviceCenterFrequency - devSampleRate/2;
}
}
deviceCenterFrequency -= calculateFrequencyShift(log2Decim, fcPos, devSampleRate);
f_img -= 2*calculateFrequencyShift(log2Decim, fcPos, devSampleRate);
qDebug() << "DeviceSampleSource::calculateDeviceCenterFrequency:"
<< " desired center freq: " << centerFrequency << " Hz"
@@ -82,3 +67,44 @@ qint64 DeviceSampleSource::calculateDeviceCenterFrequency(
return deviceCenterFrequency;
}
/**
* log2Decim = 0: no shift
*
* n = log2Decim <= 2: fc = +/- 1/2^(n-1)
* center
* | ^ |
* | inf | sup |
* ^ ^
*
* n = log2Decim > 2: fc = +/- 1/2^n
* center
* | ^ |
* | |inf| | |sup| |
* ^ ^
*/
qint32 DeviceSampleSource::calculateFrequencyShift(
int log2Decim,
fcPos_t fcPos,
quint32 devSampleRate)
{
if (log2Decim == 0) { // no shift at all
return 0;
} else if (log2Decim < 3) {
if (fcPos == FC_POS_INFRA) { // shift in the square next to center frequency
return -(devSampleRate / (1<<(log2Decim+1)));
} else if (fcPos == FC_POS_SUPRA) {
return devSampleRate / (1<<(log2Decim+1));
} else {
return 0;
}
} else {
if (fcPos == FC_POS_INFRA) { // shift centered in the square next to center frequency
return -(devSampleRate / (1<<(log2Decim)));
} else if (fcPos == FC_POS_SUPRA) {
return devSampleRate / (1<<(log2Decim));
} else {
return 0;
}
}
}