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Change order of sub-band matching in the Downchannelizer. Fixes possible aliasing issues. Fixes #1846

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f4exb 2023-10-15 11:50:31 +02:00
parent 8c98a48092
commit 8ca7dbbd4e
1 changed files with 12 additions and 12 deletions
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24
sdrbase/dsp/downchannelizer.cpp
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@ -233,12 +233,20 @@ Real DownChannelizer::createFilterChain(Real sigStart, Real sigEnd, Real chanSta
Real sigBw = sigEnd - sigStart; Real sigBw = sigEnd - sigStart;
Real rot = sigBw / 4; Real rot = sigBw / 4;
//qDebug("DownChannelizer::createFilterChain: Signal [%.1f, %.1f] (BW %.1f), Channel [%.1f, %.1f], Rot %.1f", sigStart, sigEnd, sigBw, chanStart, chanEnd, rot); qDebug("DownChannelizer::createFilterChain: Signal [%.1f, %.1f] (BW %.1f), Channel [%.1f, %.1f], Rot %.1f", sigStart, sigEnd, sigBw, chanStart, chanEnd, rot);
// check if it fits into the center
if(signalContainsChannel(sigStart + rot, sigEnd - rot, chanStart, chanEnd))
{
qDebug("DownChannelizer::createFilterChain: -> take center half (decimate by 2)");
m_filterStages.push_back(new FilterStage(FilterStage::ModeCenter));
return createFilterChain(sigStart + rot, sigEnd - rot, chanStart, chanEnd);
}
// check if it fits into the left half // check if it fits into the left half
if(signalContainsChannel(sigStart, sigStart + sigBw / 2.0, chanStart, chanEnd)) if(signalContainsChannel(sigStart, sigStart + sigBw / 2.0, chanStart, chanEnd))
{ {
//qDebug("DownChannelizer::createFilterChain: -> take left half (rotate by +1/4 and decimate by 2)"); qDebug("DownChannelizer::createFilterChain: -> take left half (rotate by +1/4 and decimate by 2)");
m_filterStages.push_back(new FilterStage(FilterStage::ModeLowerHalf)); m_filterStages.push_back(new FilterStage(FilterStage::ModeLowerHalf));
return createFilterChain(sigStart, sigStart + sigBw / 2.0, chanStart, chanEnd); return createFilterChain(sigStart, sigStart + sigBw / 2.0, chanStart, chanEnd);
} }
@ -246,21 +254,13 @@ Real DownChannelizer::createFilterChain(Real sigStart, Real sigEnd, Real chanSta
// check if it fits into the right half // check if it fits into the right half
if(signalContainsChannel(sigEnd - sigBw / 2.0f, sigEnd, chanStart, chanEnd)) if(signalContainsChannel(sigEnd - sigBw / 2.0f, sigEnd, chanStart, chanEnd))
{ {
//qDebug("DownChannelizer::createFilterChain: -> take right half (rotate by -1/4 and decimate by 2)"); qDebug("DownChannelizer::createFilterChain: -> take right half (rotate by -1/4 and decimate by 2)");
m_filterStages.push_back(new FilterStage(FilterStage::ModeUpperHalf)); m_filterStages.push_back(new FilterStage(FilterStage::ModeUpperHalf));
return createFilterChain(sigEnd - sigBw / 2.0f, sigEnd, chanStart, chanEnd); return createFilterChain(sigEnd - sigBw / 2.0f, sigEnd, chanStart, chanEnd);
} }
// check if it fits into the center
if(signalContainsChannel(sigStart + rot, sigEnd - rot, chanStart, chanEnd))
{
//qDebug("DownChannelizer::createFilterChain: -> take center half (decimate by 2)");
m_filterStages.push_back(new FilterStage(FilterStage::ModeCenter));
return createFilterChain(sigStart + rot, sigEnd - rot, chanStart, chanEnd);
}
Real ofs = ((chanEnd - chanStart) / 2.0 + chanStart) - ((sigEnd - sigStart) / 2.0 + sigStart); Real ofs = ((chanEnd - chanStart) / 2.0 + chanStart) - ((sigEnd - sigStart) / 2.0 + sigStart);
//qDebug("DownChannelizer::createFilterChain: -> complete (final BW %.1f, frequency offset %.1f)", sigBw, ofs); qDebug("DownChannelizer::createFilterChain: -> complete (final BW %.1f, frequency offset %.1f)", sigBw, ofs);
return ofs; return ofs;
} }