Log option for frequency sweep

Software/PC_Application/VNA/vna.cpp

@@ -298,6 +298,12 @@ VNA::VNA(AppWindow *window)
     connect(bZoomOut, &QPushButton::clicked, this, &VNA::SpanZoomOut);
     frequencySweepActions.push_back(tb_sweep->addWidget(bZoomOut));
 
+    auto cbLogSweep = new  QCheckBox("Log");
+    cbLogSweep->setToolTip("Logarithmic sweep");
+    connect(cbLogSweep, &QCheckBox::toggled, this, &VNA::SetLogSweep);
+    connect(this, &VNA::logSweepChanged, cbLogSweep, &QCheckBox::setChecked);
+    frequencySweepActions.push_back(tb_sweep->addWidget(cbLogSweep));
+
     // power sweep widgets
     auto sbPowerLow = new QDoubleSpinBox();
     width = QFontMetrics(sbPowerLow->font()).width("-30.00dBm") + 20;
@@ -700,6 +706,7 @@ nlohmann::json VNA::toJSON()
     freq["start"] = settings.Freq.start;
     freq["stop"] = settings.Freq.stop;
     freq["power"] = settings.Freq.excitation_power;
+    freq["log"] = settings.Freq.logSweep;
     sweep["frequency"] = freq;
     nlohmann::json power;
     power["start"] = settings.Power.start;
@@ -750,6 +757,7 @@ void VNA::fromJSON(nlohmann::json j)
             SetStartFreq(freq.value("start", settings.Freq.start));
             SetStopFreq(freq.value("stop", settings.Freq.stop));
             SetSourceLevel(freq.value("power", settings.Freq.excitation_power));
+            SetLogSweep(freq.value("log", settings.Freq.logSweep));
         }
         if(sweep.contains("power")) {
             auto power = sweep["power"];
@@ -850,6 +858,7 @@ void VNA::SettingsChanged(std::function<void (Device::TransmissionResult)> cb)
         s.if_bandwidth = settings.bandwidth;
         s.cdbm_excitation_start = settings.Freq.excitation_power * 100;
         s.cdbm_excitation_stop = settings.Freq.excitation_power * 100;
+        s.logSweep = settings.Freq.logSweep;
     } else if(settings.sweepType == SweepType::Power) {
         s.fixedPowerSetting = 0;
         s.f_start = settings.Power.frequency;
@@ -858,6 +867,7 @@ void VNA::SettingsChanged(std::function<void (Device::TransmissionResult)> cb)
         s.if_bandwidth = settings.bandwidth;
         s.cdbm_excitation_start = settings.Power.start * 100;
         s.cdbm_excitation_stop = settings.Power.stop * 100;
+        s.logSweep = false;
     }
     if(window->getDevice() && Mode::getActiveMode() == this) {
         if(s.excitePort1 == 0 && s.excitePort2 == 0) {
@@ -979,6 +989,16 @@ void VNA::SpanZoomOut()
     ConstrainAndUpdateFrequencies();
 }
 
+void VNA::SetLogSweep(bool log)
+{
+    if(settings.Freq.logSweep != log) {
+        settings.Freq.logSweep = log;
+        emit logSweepChanged(log);
+        SettingsChanged();
+    }
+}
+
+
 void VNA::SetSourceLevel(double level)
 {
     if(level > Device::Info().limits_cdbm_max / 100.0) {
@@ -1500,3 +1520,4 @@ VNA::SweepType VNA::SweepTypeFromString(QString s)
     // not found
     return SweepType::Last;
 }
+

Software/PC_Application/VNA/vna.h

@@ -46,6 +46,7 @@ public:
             double start;
             double stop;
             double excitation_power;
+            bool logSweep;
         } Freq;
         struct {
             double start;
@@ -70,6 +71,8 @@ private slots:
     void SetFullSpan();
     void SpanZoomIn();
     void SpanZoomOut();
+
+    void SetLogSweep(bool log);
     // Acquisition control
     void SetSourceLevel(double level);
     // Power sweep settings
@@ -146,6 +149,7 @@ signals:
     void stopFreqChanged(double freq);
     void centerFreqChanged(double freq);
     void spanChanged(double span);
+    void logSweepChanged(bool log);
 
     void sourceLevelChanged(double level);
     void pointsChanged(unsigned int points);

Software/PC_Application/preferences.h

@@ -35,6 +35,7 @@ public:
             QString type;
             double f_start;
             double f_stop;
+            bool logSweep;
             double f_excitation;
 
             double dbm_start;
@@ -103,12 +104,13 @@ private:
         QString name;
         QVariant def;
     };
-    const std::array<SettingDescription, 40> descr = {{
+    const std::array<SettingDescription, 41> descr = {{
         {&Startup.ConnectToFirstDevice, "Startup.ConnectToFirstDevice", true},
         {&Startup.RememberSweepSettings, "Startup.RememberSweepSettings", false},
         {&Startup.DefaultSweep.type, "Startup.DefaultSweep.type", "Frequency"},
         {&Startup.DefaultSweep.f_start, "Startup.DefaultSweep.start", 1000000.0},
         {&Startup.DefaultSweep.f_stop, "Startup.DefaultSweep.stop", 6000000000.0},
+        {&Startup.DefaultSweep.logSweep, "Startup.DefaultSweep.logSweep", false},
         {&Startup.DefaultSweep.f_excitation, "Startup.DefaultSweep.excitation", -10.00},
         {&Startup.DefaultSweep.dbm_start, "Startup.DefaultSweep.dbm_start", -30.00},
         {&Startup.DefaultSweep.dbm_stop, "Startup.DefaultSweep.dbm_stop", -10.0},

Software/VNA_embedded/Application/Communication/Protocol.hpp

@@ -4,7 +4,7 @@
 
 namespace Protocol {
 
-static constexpr uint16_t Version = 7;
+static constexpr uint16_t Version = 8;
 
 #pragma pack(push, 1)
 
@@ -28,6 +28,7 @@ using SweepSettings = struct _sweepSettings {
 	uint8_t excitePort2:1;
 	uint8_t suppressPeaks:1;
 	uint8_t fixedPowerSetting:1; // if set the attenuator and source PLL power will not be changed across the sweep
+	uint8_t logSweep:1;
     int16_t cdbm_excitation_stop; // in 1/100 dbm
 };
 

Software/VNA_embedded/Application/VNA.cpp

@@ -13,6 +13,7 @@
 #include "task.h"
 #include "Util.hpp"
 #include "usb.h"
+#include <cmath>
 
 #define LOG_LEVEL	LOG_LEVEL_INFO
 #define LOG_MODULE	"VNA"
@@ -20,6 +21,7 @@
 
 static Protocol::SweepSettings settings;
 static uint16_t pointCnt;
+static float span_log10;
 static bool excitingPort1;
 static Protocol::Datapoint data;
 static bool active = false;
@@ -51,6 +53,14 @@ static constexpr uint32_t reservedUSBbuffer = maxPointsBetweenHalts * (sizeof(Pr
 
 using namespace HWHAL;
 
+static uint64_t getPointFrequency(uint16_t pointNum) {
+	if(!settings.logSweep) {
+		return settings.f_start + (settings.f_stop - settings.f_start) * pointNum / (settings.points - 1);
+	} else {
+		return settings.f_start * powf(10.0, pointNum * span_log10 / (settings.points - 1));
+	}
+}
+
 bool VNA::Setup(Protocol::SweepSettings s) {
 	VNA::Stop();
 	vTaskDelay(5);
@@ -62,11 +72,14 @@ bool VNA::Setup(Protocol::SweepSettings s) {
 		return false;
 	}
 	settings = s;
+	span_log10 = log10((double) settings.f_stop / settings.f_start);
 	// Abort possible active sweep first
 	FPGA::SetMode(FPGA::Mode::FPGA);
-	uint16_t points = settings.points <= FPGA::MaxPoints ? settings.points : FPGA::MaxPoints;
+	if(settings.points > FPGA::MaxPoints) {
+		settings.points = FPGA::MaxPoints;
+	}
 	// Configure sweep
-	FPGA::SetNumberOfPoints(points);
+	FPGA::SetNumberOfPoints(settings.points);
 	uint32_t samplesPerPoint = (HW::ADCSamplerate / s.if_bandwidth);
 	// round up to next multiple of 16 (16 samples are spread across 5 IF2 periods)
 	if(samplesPerPoint%16) {
@@ -120,10 +133,10 @@ bool VNA::Setup(Protocol::SweepSettings s) {
 	uint16_t pointsWithoutHalt = 0;
 
 	// Transfer PLL configuration to FPGA
-	for (uint16_t i = 0; i < points; i++) {
+	for (uint16_t i = 0; i < settings.points; i++) {
 		bool harmonic_mixing = false;
-		uint64_t freq = s.f_start + (s.f_stop - s.f_start) * i / (points - 1);
+		uint64_t freq = getPointFrequency(i);
-		int16_t power = s.cdbm_excitation_start + (s.cdbm_excitation_stop - s.cdbm_excitation_start) * i / (points - 1);
+		int16_t power = s.cdbm_excitation_start + (s.cdbm_excitation_stop - s.cdbm_excitation_start) * i / (settings.points - 1);
 		freq = Cal::FrequencyCorrectionToDevice(freq);
 
 		if(freq > 6000000000ULL) {
@@ -286,7 +299,7 @@ bool VNA::MeasurementDone(const FPGA::SamplingResult &result) {
 	auto port1 = port1_raw / ref;
 	auto port2 = port2_raw / ref;
 	data.pointNum = pointCnt;
-	data.frequency = settings.f_start + (settings.f_stop - settings.f_start) * pointCnt / (settings.points - 1);
+	data.frequency = getPointFrequency(pointCnt);
 	data.cdbm = settings.cdbm_excitation_start + (settings.cdbm_excitation_stop - settings.cdbm_excitation_start) * pointCnt / (settings.points - 1);
 	if(excitingPort1) {
 		data.real_S11 = port1.real();
@@ -352,9 +365,7 @@ void VNA::SweepHalted() {
 		// PLL reset causes the 2.LO to turn off briefly and then ramp on back, needs delay before next point
 		Delay::us(1300);
 	}
-	uint64_t frequency = settings.f_start
+	uint64_t frequency = getPointFrequency(pointCnt);
-			+ (settings.f_stop - settings.f_start) * pointCnt
-					/ (settings.points - 1);
 	int16_t power = settings.cdbm_excitation_start
 			+ (settings.cdbm_excitation_stop - settings.cdbm_excitation_start)
 					* pointCnt / (settings.points - 1);