diff --git a/sdrbase/CMakeLists.txt b/sdrbase/CMakeLists.txt
index 5bacdd135..da49b3469 100644
--- a/sdrbase/CMakeLists.txt
+++ b/sdrbase/CMakeLists.txt
@@ -28,6 +28,7 @@ set(sdrbase_SOURCES
dsp/dspengine.cpp
dsp/dspdevicesourceengine.cpp
dsp/dspdevicesinkengine.cpp
+ dsp/fftcorr.cpp
dsp/fftengine.cpp
dsp/fftfilt.cxx
dsp/fftwindow.cpp
@@ -118,6 +119,7 @@ set(sdrbase_HEADERS
dsp/dspdevicesourceengine.h
dsp/dspdevicesinkengine.h
dsp/dsptypes.h
+ dsp/fftcorr.h
dsp/fftengine.h
dsp/fftfilt.h
dsp/fftwengine.h
diff --git a/sdrbase/dsp/fftcorr.cpp b/sdrbase/dsp/fftcorr.cpp
new file mode 100644
index 000000000..22fa00ba4
--- /dev/null
+++ b/sdrbase/dsp/fftcorr.cpp
@@ -0,0 +1,112 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2018 F4EXB //
+// written by Edouard Griffiths //
+// //
+// FFT based cross correlation //
+// //
+// See: http://liquidsdr.org/blog/pll-howto/ //
+// Fixed filter registers saturation //
+// Added order for PSK locking. This brilliant idea actually comes from this //
+// post: https://www.dsprelated.com/showthread/comp.dsp/36356-1.php //
+// //
+// 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 . //
+///////////////////////////////////////////////////////////////////////////////////
+
+#include
+#include "fftcorr.h"
+
+void fftcorr::init_fft()
+{
+ flen2 = flen >> 1;
+ fftA = new g_fft(flen);
+ fftB = new g_fft(flen);
+
+ dataA = new cmplx[flen];
+ dataB = new cmplx[flen];
+ dataBj = new cmplx[flen];
+ dataP = new cmplx[flen];
+ output = new cmplx[flen2];
+ ovlbuf = new cmplx[flen2];
+
+ std::fill(dataA, dataA+flen, 0);
+ std::fill(dataB, dataB+flen, 0);
+ std::fill(output, output+flen2, 0);
+ std::fill(ovlbuf, ovlbuf+flen2, 0);
+
+ inptrA = 0;
+ inptrB = 0;
+}
+
+fftcorr::fftcorr(int len) : flen(len), flen2(len>>1)
+{
+ init_fft();
+}
+
+fftcorr::~fftcorr()
+{
+ delete fftA;
+ delete fftB;
+ delete[] dataA;
+ delete[] dataB;
+ delete[] dataBj;
+ delete[] dataP;
+ delete[] output;
+ delete[] ovlbuf;
+}
+
+int fftcorr::run(const cmplx& inA, const cmplx* inB, cmplx **out)
+{
+ dataA[inptrA++] = inA;
+
+ if (inB) {
+ dataB[inptrB++] = *inB;
+ }
+
+ if (inptrA < flen2) {
+ return 0;
+ }
+
+ fftA->ComplexFFT(dataA);
+
+ if (inB) {
+ fftB->ComplexFFT(dataB);
+ }
+
+ if (inB) {
+ std::transform(dataB, dataB+flen, dataBj, [](const cmplx& c) -> cmplx { return std::conj(c); });
+ } else {
+ std::transform(dataA, dataA+flen, dataBj, [](const cmplx& c) -> cmplx { return std::conj(c); });
+ }
+
+ std::transform(dataA, dataA+flen, dataBj, dataP, [](const cmplx& a, const cmplx& b) -> cmplx { return a*b; });
+
+ fftA->InverseComplexFFT(dataP);
+
+ for (int i = 0; i < flen2; i++)
+ {
+ output[i] = ovlbuf[i] + dataP[i];
+ ovlbuf[i] = dataP[flen2 + i];
+ }
+
+ std::fill(dataA, dataA+flen, 0);
+ inptrA = 0;
+
+ if (inB)
+ {
+ std::fill(dataB, dataB+flen, 0);
+ inptrB = 0;
+ }
+
+ *out = output;
+ return flen2;
+}
diff --git a/sdrbase/dsp/fftcorr.h b/sdrbase/dsp/fftcorr.h
new file mode 100644
index 000000000..cd7777340
--- /dev/null
+++ b/sdrbase/dsp/fftcorr.h
@@ -0,0 +1,57 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2018 F4EXB //
+// written by Edouard Griffiths //
+// //
+// FFT based cross correlation //
+// //
+// See: http://liquidsdr.org/blog/pll-howto/ //
+// Fixed filter registers saturation //
+// Added order for PSK locking. This brilliant idea actually comes from this //
+// post: https://www.dsprelated.com/showthread/comp.dsp/36356-1.php //
+// //
+// 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 . //
+///////////////////////////////////////////////////////////////////////////////////
+
+#ifndef SDRBASE_DSP_FFTCORR_H_
+#define SDRBASE_DSP_FFTCORR_H_
+
+#include
+#include "gfft.h"
+#include "export.h"
+
+class SDRBASE_API fftcorr {
+public:
+ typedef std::complex cmplx;
+ fftcorr(int len);
+ ~fftcorr();
+
+ int run(const cmplx& inA, const cmplx* inB, cmplx **out); //!< if inB = 0 then run auto-correlation
+
+private:
+ void init_fft();
+ int flen; //!< FFT length
+ int flen2; //!< half FFT length
+ g_fft *fftA;
+ g_fft *fftB;
+ cmplx *dataA; // from A input
+ cmplx *dataB; // from B input
+ cmplx *dataBj; // conjugate of B
+ cmplx *dataP; // product of A with conjugate of B
+ cmplx *ovlbuf;
+ cmplx *output;
+ int inptrA;
+ int inptrB;
+};
+
+
+#endif /* SDRBASE_DSP_FFTCORR_H_ */