diff --git a/Detector.cpp b/Detector.cpp
new file mode 100644
index 000000000..bf3f4b8cb
--- /dev/null
+++ b/Detector.cpp
@@ -0,0 +1,93 @@
+#include "Detector.hpp"
+
+#include <algorithm>
+
+#include <QDateTime>
+#include <QDebug>
+
+#include "commons.h"
+
+Detector::Detector (unsigned frameRate, unsigned periodLengthInSeconds, unsigned bytesPerSignal, QObject * parent)
+  : QIODevice (parent)
+  , m_frameRate (frameRate)
+  , m_period (periodLengthInSeconds)
+  , m_bytesPerSignal (bytesPerSignal)
+  , m_monitoring (false)
+  , m_starting (false)
+{
+  clear ();
+}
+
+bool Detector::reset ()
+{
+  clear ();
+  return QIODevice::reset ();
+}
+
+void Detector::clear ()
+{
+  // set index to roughly where we are in time (1s resolution)
+  jt9com_.kin = secondInPeriod () * m_frameRate;
+
+  // fill buffer with zeros
+  std::fill (jt9com_.d2, jt9com_.d2 + sizeof (jt9com_.d2) / sizeof (jt9com_.d2[0]), 0);
+}
+
+qint64 Detector::writeData (char const * data, qint64 maxSize)
+{
+  Q_ASSERT (!(maxSize % sizeof (jt9com_.d2[0]))); // no torn frames
+  Q_ASSERT (!(reinterpret_cast<size_t> (data) % __alignof__ (frame_t)));	  // data is aligned as frame_t would be
+
+  frame_t const * frames (reinterpret_cast<frame_t const *> (data));
+
+  qint64 framesAcceptable (sizeof (jt9com_.d2) / sizeof (jt9com_.d2[0]) - jt9com_.kin);
+  qint64 framesAccepted (std::min (maxSize / sizeof (jt9com_.d2[0]), framesAcceptable));
+  
+  if (framesAccepted < maxSize / sizeof (jt9com_.d2[0]))
+    {
+      qDebug () << "dropped " << maxSize / sizeof (jt9com_.d2[0]) - framesAccepted << " frames of data on the floor!\n";
+    }
+
+  std::copy (frames, frames + framesAccepted, &jt9com_.d2[jt9com_.kin]);
+
+  unsigned lastSignalIndex (jt9com_.kin * sizeof (jt9com_.d2[0]) / m_bytesPerSignal);
+  jt9com_.kin += framesAccepted;
+  unsigned currentSignalIndex (jt9com_.kin * sizeof (jt9com_.d2[0]) / m_bytesPerSignal);
+
+  if (currentSignalIndex != lastSignalIndex && m_monitoring)
+    {
+      Q_EMIT bytesWritten (currentSignalIndex * m_bytesPerSignal);
+    }
+
+  if (!secondInPeriod ())
+    {
+      if (!m_starting)
+	{
+	  // next samples will be in new period so wrap around to
+	  // start of buffer
+	  //
+	  // we don't bother calling reset () since we expect to fill
+	  // the whole buffer and don't need to waste cycles zeroing
+	  jt9com_.kin = 0;
+	  m_starting = true;
+	}
+    }
+  else if (m_starting)
+    {
+      m_starting = false;
+    }
+
+  return maxSize;		// we drop any data past the end of
+				// the buffer on the floor until the
+				// next period starts
+}
+
+unsigned Detector::secondInPeriod () const
+{
+  // we take the time of the data as the following assuming no latency
+  // delivering it to us (not true but close enough for us)
+  qint64 now (QDateTime::currentMSecsSinceEpoch ());
+
+  unsigned secondInToday ((now % 86400000LL) / 1000);
+  return secondInToday % m_period;
+}
diff --git a/Detector.hpp b/Detector.hpp
new file mode 100644
index 000000000..7ddb08121
--- /dev/null
+++ b/Detector.hpp
@@ -0,0 +1,67 @@
+#ifndef DETECTOR_HPP__
+#define DETECTOR_HPP__
+
+#include <inttypes.h>
+
+#include <QIODevice>
+
+//
+// output device that distributes data in predefined chunks via a signal
+//
+// the underlying device for this abstraction is just the buffer that
+// stores samples throughout a receiving period
+//
+class Detector : public QIODevice
+{
+  Q_OBJECT;
+
+  Q_PROPERTY (bool monitoring READ isMonitoring WRITE setMonitoring);
+
+private:
+  Q_DISABLE_COPY (Detector);
+
+public:
+  //
+  // if the data buffer were not global storage and fixed size then we
+  // might want maximum size passed as constructor arguments
+  //
+  Detector (unsigned frameRate, unsigned periodLengthInSeconds, unsigned bytesPerSignal, QObject * parent = 0);
+
+  bool open ()
+  {
+    // we only support data consumption and want it as fast as possible
+    return QIODevice::open (QIODevice::WriteOnly | QIODevice::Unbuffered);
+  }
+
+  bool isSequential () const
+  {
+    return true;
+  }
+
+  bool isMonitoring () const {return m_monitoring;}
+  void setMonitoring (bool newState) {m_monitoring = newState;}
+
+  bool reset ();
+
+protected:
+  qint64 readData (char * /* data */, qint64 /* maxSize */)
+  {
+    return -1;			// we don't produce data
+  }
+
+  qint64 writeData (char const * data, qint64 maxSize);
+
+private:
+  typedef int16_t frame_t;
+
+  void clear ();		// discard buffer contents
+  unsigned secondInPeriod () const;
+
+  unsigned m_frameRate;
+  unsigned m_period;
+  unsigned m_bytesPerSignal;
+  bool m_monitoring;
+  bool m_starting;
+};
+
+#endif
diff --git a/Modulator.cpp b/Modulator.cpp
new file mode 100644
index 000000000..c1178b6f8
--- /dev/null
+++ b/Modulator.cpp
@@ -0,0 +1,195 @@
+#include "Modulator.hpp"
+
+#include <cstdlib>
+#include <cmath>
+#include <algorithm>
+#include <limits>
+
+#include <QDateTime>
+
+extern float gran();		// Noise generator (for tests only)
+
+double const Modulator::m_twoPi = 2.0 * 3.141592653589793238462;
+
+//    float wpm=20.0;
+//    unsigned m_nspd=1.2*48000.0/wpm;
+//    m_nspd=3072;                           //18.75 WPM
+unsigned const Modulator::m_nspd = 2048 + 512; // 22.5 WPM
+
+Modulator::Modulator (unsigned frameRate, unsigned periodLengthInSeconds, QObject * parent)
+  : QIODevice (parent)
+  , m_frameRate (frameRate)
+  , m_period (periodLengthInSeconds)
+  , m_state (Idle)
+  , m_phi (0.)
+  , m_ic (0)
+  , m_isym0 (std::numeric_limits<unsigned>::max ()) // ensure we set up first symbol tone
+{
+}
+
+bool Modulator::open (std::vector<int> const * symbols, std::vector<int> const * cw, double framesPerSymbol, unsigned frequency, double dBSNR)
+{
+  m_symbols.reset (symbols);	// take over ownership (cannot throw)
+  m_cw.reset (cw);		// take over ownership (cannot throw)
+  m_addNoise = dBSNR < 0.;
+  m_nsps = framesPerSymbol;
+  m_frequency = frequency;
+  m_amp = std::numeric_limits<frame_t>::max ();
+  m_state = Idle;
+
+  // noise generator parameters
+  if (m_addNoise)
+    {
+      m_snr = std::pow (10.0, 0.05 * (dBSNR - 6.0));
+      m_fac = 3000.0;
+      if (m_snr > 1.0)
+	{
+	  m_fac = 3000.0 / m_snr;
+	}
+    }
+  
+  return QIODevice::open (QIODevice::ReadOnly);
+}
+
+qint64 Modulator::readData (char * data, qint64 maxSize)
+{
+  frame_t * frames (reinterpret_cast<frame_t *> (data));
+  unsigned numFrames (maxSize / sizeof (frame_t));
+
+  switch (m_state)
+    {
+    case Idle:
+      {
+	// Time according to this computer
+	qint64 ms = QDateTime::currentMSecsSinceEpoch() % 86400000;
+	unsigned mstr = ms % (1000 * m_period);
+	if (mstr < 1000)	// send silence up to first second
+	  {
+	    std::fill (frames, frames + numFrames, 0);		 // silence
+	    return numFrames * sizeof (frame_t);
+	  }
+	m_ic = (mstr - 1000) * 48;
+
+	std::srand (mstr);		// Initialize random seed
+
+	m_state = Active;
+      }
+      // fall through
+
+    case Active:
+      {
+	unsigned isym (m_tuning ? 0 : m_ic / (4.0 * m_nsps)); // Actual fsample=48000
+
+	if (isym >= m_symbols->size () && (*m_cw)[0] > 0)
+	  {
+	    // Output the CW ID
+	    m_dphi = m_twoPi * m_frequency / m_frameRate;
+
+	    unsigned const ic0 = m_symbols->size () * 4 * m_nsps;
+	    unsigned j (0);
+	    for (unsigned i = 0; i < numFrames; ++i)
+	      {
+		m_phi += m_dphi;
+		if (m_phi > m_twoPi)
+		  {
+		    m_phi -= m_twoPi;
+		  }
+		frame_t frame = std::numeric_limits<frame_t>::max () * std::sin (m_phi);
+		j = (m_ic - ic0) / m_nspd + 1;
+		if (!(*m_cw)[j])
+		  {
+		    frame = 0;
+		  }
+
+		frame = postProcessFrame (frame);
+
+		*frames++ = frame; //left
+		++m_ic;
+	      }
+	    if (j > static_cast<unsigned> ((*m_cw)[0]))
+	      {
+		m_state = Done;
+	      }
+	    return numFrames * sizeof (frame_t);
+	  }
+
+	double const baud (12000.0 / m_nsps);
+
+	// fade out parameters (no fade out for tuning)
+	unsigned const i0 = m_tuning ? 999 * m_nsps : (m_symbols->size () - 0.017) * 4.0 * m_nsps;
+	unsigned const i1 = m_tuning ? 999 * m_nsps : m_symbols->size () * 4.0 * m_nsps;
+
+	for (unsigned i = 0; i < numFrames; ++i)
+	  {
+	    isym = m_tuning ? 0 : m_ic / (4.0 * m_nsps); //Actual fsample=48000
+	    if (isym != m_isym0)
+	      {
+		double toneFrequency = m_frequency + (*m_symbols)[isym] * baud;
+		m_dphi = m_twoPi * toneFrequency / m_frameRate;
+		m_isym0 = isym;
+	      }
+	    m_phi += m_dphi;
+	    if (m_phi > m_twoPi)
+	      {
+		m_phi -= m_twoPi;
+	      }
+	    if (m_ic > i0)
+	      {
+		m_amp = 0.98 * m_amp;
+	      }
+	    if (m_ic > i1)
+	      {
+		m_amp = 0.0;
+	      }
+	    frame_t frame (m_amp * std::sin (m_phi));
+	    frame = postProcessFrame (frame);
+	    *frames++ = frame;	//left
+	    ++m_ic;
+	  }
+
+	if (m_amp == 0.0) // TODO G4WJS: compare double with zero might not be wise
+	  {
+	    if ((*m_cw)[0] == 0)
+	      {
+		// no CW ID to send
+		m_state = Done;
+		return numFrames * sizeof (frame_t);
+	      }
+
+	    m_phi = 0.0;
+	  }
+
+	// done for this chunk - continue on next call
+	return numFrames * sizeof (frame_t);
+      }
+
+    case Done:
+      break;
+    }
+
+  Q_ASSERT (m_state == Done);
+  return 0;
+}
+
+Modulator::frame_t Modulator::postProcessFrame (frame_t frame) const
+{
+  if (m_muted)			// silent frame
+    {
+      return 0;
+    }
+
+  if (m_addNoise)
+    {
+      int i4 = m_fac * (gran () + frame * m_snr / 32768.0);
+      if (i4 > std::numeric_limits<frame_t>::max ())
+	{
+	  i4 = std::numeric_limits<frame_t>::max ();
+	}
+      if (i4 < std::numeric_limits<frame_t>::min ())
+	{
+	  i4 = std::numeric_limits<frame_t>::min ();
+	}
+      frame = i4;
+    }
+  return frame;
+}
diff --git a/Modulator.hpp b/Modulator.hpp
new file mode 100644
index 000000000..24b7a17bb
--- /dev/null
+++ b/Modulator.hpp
@@ -0,0 +1,81 @@
+#ifndef MODULATOR_HPP__
+#define MODULATOR_HPP__
+
+#include <vector>
+
+#include <QIODevice>
+#include <QScopedPointer>
+
+//
+// Input device that generates PCM audio frames that encode a message
+// and an optional CW ID.
+//
+// Output can be muted while underway, preserving waveform timing when
+// transmission is resumed.
+//
+class Modulator : public QIODevice
+{
+  Q_OBJECT;
+
+  Q_PROPERTY (unsigned frequency READ frequency WRITE setFrequency);
+  Q_PROPERTY (bool tuning READ isTuning WRITE tune);
+  Q_PROPERTY (bool muted READ isMuted WRITE mute);
+
+private:
+  Q_DISABLE_COPY (Modulator);
+
+public:
+  Modulator (unsigned frameRate, unsigned periodLengthInSeconds, QObject * parent = 0);
+
+  bool isTuning () const {return m_tuning;}
+  Q_SLOT void tune (bool newState = true) {m_tuning = newState;}
+
+  bool isMuted () const {return m_muted;}
+  Q_SLOT void mute (bool newState = true) {m_muted = newState;}
+
+  unsigned frequency () const {return m_frequency;}
+  Q_SLOT void setFrequency (unsigned newFrequency) {m_frequency = newFrequency;}
+
+  bool open (std::vector<int> const * symbols, std::vector<int> const * cw, double framesPerSymbol, unsigned frequency, double dBSNR = 99.);
+
+  bool isSequential () const
+  {
+    return true;
+  }
+
+protected:
+  qint64 readData (char * data, qint64 maxSize);
+  qint64 writeData (char const * /* data */, qint64 /* maxSize */)
+  {
+    return -1;			// we don't consume data
+  }
+
+private:
+  typedef short frame_t;
+
+  frame_t postProcessFrame (frame_t frame) const;
+
+  QScopedPointer<std::vector<int> const> m_symbols;
+  QScopedPointer<std::vector<int> const> m_cw;
+
+  static double const m_twoPi;
+  static unsigned const m_nspd;	// CW ID WPM factor
+
+  int m_frameRate;
+  int m_period;
+  double m_nsps;
+  double m_frequency;
+  double m_snr;
+  enum {Idle, Active, Done} m_state;
+  bool m_tuning;
+  bool m_muted;
+  bool m_addNoise;
+  double m_phi;
+  double m_dphi;
+  double m_amp;
+  unsigned m_ic;
+  double m_fac;
+  unsigned m_isym0;
+};
+
+#endif
diff --git a/mainwindow.cpp b/mainwindow.cpp
index f9c8335c9..5322b7aa6 100644
--- a/mainwindow.cpp
+++ b/mainwindow.cpp
@@ -1,4 +1,4 @@
-//--------------------------------------------------------------- MainWindow
+//---------------------------------------------------------------- MainWindow
 #include "mainwindow.h"
 #include "ui_mainwindow.h"