diff --git a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.cpp b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.cpp
index 8311035..bd5239e 100644
--- a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.cpp
@@ -13,6 +13,8 @@
 CompoundDriver::CompoundDriver()
 {
     connected = false;
+    isIdle = true;
+    triggerForwarding = false;
     SApoints = 0;
 
     drivers.push_back(new LibreVNAUSBDriver);
@@ -296,6 +298,11 @@ bool CompoundDriver::setVNA(const DeviceDriver::VNASettings &s, std::function<vo
         return setIdle(cb);
     }
 
+    setIdle([this](bool){
+        enableTriggerForwarding();
+        qDebug() << "Start trigger forwarding";
+    });
+
     // create port->stage mapping
     portStageMapping.clear();
     for(unsigned int i=0;i<s.excitedPorts.size();i++) {
@@ -334,6 +341,11 @@ bool CompoundDriver::setVNA(const DeviceDriver::VNASettings &s, std::function<vo
             }
         });
     }
+
+    lastNonIdleSettings.type = lastNonIdleSettings.Types::VNA;
+    lastNonIdleSettings.vna = s;
+    isIdle = false;
+
     return success;
 }
 
@@ -353,6 +365,11 @@ bool CompoundDriver::setSA(const DeviceDriver::SASettings &s, std::function<void
     }
     zerospan = s.freqStart == s.freqStop;
 
+    setIdle([this](bool){
+        enableTriggerForwarding();
+        qDebug() << "Start trigger forwarding";
+    });
+
     // Configure the devices
     results.clear();
     bool success = true;
@@ -385,6 +402,11 @@ bool CompoundDriver::setSA(const DeviceDriver::SASettings &s, std::function<void
             break;
         }
     }
+
+    lastNonIdleSettings.type = lastNonIdleSettings.Types::SA;
+    lastNonIdleSettings.sa = s;
+    isIdle = false;
+
     return success;
 }
 
@@ -415,14 +437,22 @@ bool CompoundDriver::setSG(const DeviceDriver::SGSettings &s)
         }
         success &= devices[i]->setSG(devSettings);
     }
+
+    lastNonIdleSettings.type = lastNonIdleSettings.Types::SG;
+    lastNonIdleSettings.sg = s;
+    isIdle = false;
+
     return success;
 }
 
 bool CompoundDriver::setIdle(std::function<void (bool)> cb)
 {
+    disableTriggerForwarding();
+    qDebug() << "Stop trigger forwarding";
     auto success = true;
     results.clear();
     for(auto dev : devices) {
+        dev->sendWithoutPayload(Protocol::PacketType::ClearTrigger);
         success &= dev->setIdle([=](bool success){
             if(cb) {
                 results[dev] = success;
@@ -430,6 +460,9 @@ bool CompoundDriver::setIdle(std::function<void (bool)> cb)
             }
         });
     }
+
+    isIdle = true;
+
     return success;
 }
 
@@ -464,9 +497,36 @@ QStringList CompoundDriver::availableExtRefOutSettings()
 bool CompoundDriver::setExtRef(QString option_in, QString option_out)
 {
     auto success = true;
-    for(auto dev : devices) {
-        success &= dev->setExtRef(option_in, option_out);
+
+    qDebug() << "Ref change start";
+    if(isIdle) {
+        // can immediately switch reference settings
+        for(auto dev : devices) {
+            success &= dev->setExtRef(option_in, option_out);
+        }
+    } else {
+        // can not switch during a sweep
+        // set to idle first
+        setIdle();
+        // change reference
+        for(auto dev : devices) {
+            success &= dev->setExtRef(option_in, option_out);
+        }
+        // restore last non idle state
+        switch(lastNonIdleSettings.type) {
+        case lastNonIdleSettings.Types::VNA:
+            setVNA(lastNonIdleSettings.vna);
+            break;
+        case lastNonIdleSettings.Types::SA:
+            setSA(lastNonIdleSettings.sa);
+            break;
+        case lastNonIdleSettings.Types::SG:
+            setSG(lastNonIdleSettings.sg);
+            break;
+        }
     }
+    qDebug() << "Ref change stop";
+
     return success;
 }
 
@@ -485,6 +545,27 @@ std::set<QString> CompoundDriver::getIndividualDeviceSerials()
     return ret;
 }
 
+void CompoundDriver::triggerReceived(LibreVNADriver *device, bool set)
+{
+    triggerMutex.lock();
+    if(activeDevice.sync == LibreVNADriver::Synchronization::GUI && triggerForwarding) {
+        for(unsigned int i=0;i<devices.size();i++) {
+            if(devices[i] == device) {
+                // pass on to the next device
+                if(i < devices.size() - 1) {
+                    qDebug() << "Passing on trigger" << set << "from" << device->getSerial() << "to" << devices[i+1]->getSerial();
+                    devices[i+1]->sendWithoutPayload(set ? Protocol::PacketType::SetTrigger : Protocol::PacketType::ClearTrigger);
+                } else {
+                    qDebug() << "Passing on trigger" << set << "from" << device->getSerial() << "to" << devices[0]->getSerial();
+                    devices[0]->sendWithoutPayload(set ? Protocol::PacketType::SetTrigger : Protocol::PacketType::ClearTrigger);
+                }
+                break;
+            }
+        }
+    }
+    triggerMutex.unlock();
+}
+
 void CompoundDriver::parseCompoundJSON()
 {
     try {
@@ -529,36 +610,6 @@ void CompoundDriver::incomingPacket(LibreVNADriver *device, const Protocol::Pack
     case Protocol::PacketType::SpectrumAnalyzerResult:
         spectrumResultReceived(device, p.spectrumResult);
         break;
-    case Protocol::PacketType::SetTrigger:
-        if(activeDevice.sync == LibreVNADriver::Synchronization::GUI) {
-            for(unsigned int i=0;i<devices.size();i++) {
-                if(devices[i] == device) {
-                    // pass on to the next device
-                    if(i < devices.size() - 1) {
-                        devices[i+1]->sendWithoutPayload(Protocol::PacketType::SetTrigger);
-                    } else {
-                        devices[0]->sendWithoutPayload(Protocol::PacketType::SetTrigger);
-                    }
-                    break;
-                }
-            }
-        }
-        break;
-    case Protocol::PacketType::ClearTrigger:
-        if(activeDevice.sync == LibreVNADriver::Synchronization::GUI) {
-            for(unsigned int i=0;i<devices.size();i++) {
-                if(devices[i] == device) {
-                    // pass on to the next device
-                    if(i < devices.size() - 1) {
-                        devices[i+1]->sendWithoutPayload(Protocol::PacketType::ClearTrigger);
-                    } else {
-                        devices[0]->sendWithoutPayload(Protocol::PacketType::ClearTrigger);
-                    }
-                    break;
-                }
-            }
-        }
-        break;
     default:
         // nothing to do for other packet types
         break;
@@ -652,6 +703,26 @@ void CompoundDriver::spectrumResultReceived(LibreVNADriver *dev, Protocol::Spect
     }
 }
 
+void CompoundDriver::enableTriggerForwarding()
+{
+    triggerMutex.lock();
+    for(auto d : devices) {
+        connect(d, &LibreVNADriver::receivedTrigger, this, &CompoundDriver::triggerReceived, Qt::UniqueConnection);
+    }
+    triggerForwarding = true;
+    triggerMutex.unlock();
+}
+
+void CompoundDriver::disableTriggerForwarding()
+{
+    triggerMutex.lock();
+    triggerForwarding = false;
+    for(auto d : devices) {
+        QObject::disconnect(d, &LibreVNADriver::receivedTrigger, this, &CompoundDriver::triggerReceived);
+    }
+    triggerMutex.unlock();
+}
+
 void CompoundDriver::datapointReceivecd(LibreVNADriver *dev, Protocol::VNADatapoint<32> *data)
 {
     if(!compoundVNABuffer.count(data->pointNum)) {
diff --git a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.h b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.h
index f21498f..2520d0f 100644
--- a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.h
+++ b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/Compound/compounddriver.h
@@ -4,6 +4,8 @@
 #include "../../devicedriver.h"
 #include "compounddevice.h"
 
+#include <QMutex>
+
 class CompoundDriver : public DeviceDriver
 {
 public:
@@ -169,6 +171,8 @@ public:
 
     static std::set<QString> getIndividualDeviceSerials();
 
+private slots:
+    void triggerReceived(LibreVNADriver *device, bool set);
 private:
     void parseCompoundJSON();
     void createCompoundJSON();
@@ -177,6 +181,8 @@ private:
     void updatedStatus(LibreVNADriver *device, const Protocol::DeviceStatus &status);
     void datapointReceivecd(LibreVNADriver *dev, Protocol::VNADatapoint<32> *data);
     void spectrumResultReceived(LibreVNADriver *dev, Protocol::SpectrumAnalyzerResult res);
+    void enableTriggerForwarding();
+    void disableTriggerForwarding();
 
     Info info;
     std::map<LibreVNADriver*, Info> deviceInfos;
@@ -196,8 +202,17 @@ private:
     // Configuration of the device we are connected to
     CompoundDevice activeDevice;
     bool connected;
+    bool triggerForwarding;
+    QMutex triggerMutex;
     std::vector<LibreVNADriver*> devices;
     bool zerospan;
+    bool isIdle;
+    struct {
+        VNASettings vna;
+        SASettings sa;
+        SGSettings sg;
+        enum class Types{VNA, SA, SG} type;
+    } lastNonIdleSettings;
     unsigned int VNApoints;
     unsigned int SApoints;
 
diff --git a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnadriver.h b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnadriver.h
index 36340c9..03f5476 100644
--- a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnadriver.h
+++ b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnadriver.h
@@ -191,6 +191,8 @@ signals:
     void receivedAnswer(const LibreVNADriver::TransmissionResult &result);
     void receivedPacket(const Protocol::PacketInfo& packet);
 
+    void receivedTrigger(LibreVNADriver *driver, bool set);
+
 protected slots:
     void handleReceivedPacket(const Protocol::PacketInfo& packet);
 protected:
diff --git a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnatcpdriver.cpp b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnatcpdriver.cpp
index a7e88a5..cde3ae6 100644
--- a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnatcpdriver.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnatcpdriver.cpp
@@ -242,6 +242,12 @@ void LibreVNATCPDriver::ReceivedData()
         case Protocol::PacketType::Nack:
             emit receivedAnswer(TransmissionResult::Nack);
             break;
+        case Protocol::PacketType::SetTrigger:
+            emit receivedTrigger(this, true);
+            break;
+        case Protocol::PacketType::ClearTrigger:
+            emit receivedTrigger(this, false);
+            break;
        default:
             // pass on to LibreVNADriver class
             emit receivedPacket(packet);
diff --git a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnausbdriver.cpp b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnausbdriver.cpp
index a0e4e66..c9d03df 100644
--- a/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnausbdriver.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Device/LibreVNA/librevnausbdriver.cpp
@@ -179,6 +179,12 @@ void LibreVNAUSBDriver::ReceivedData()
             }
         }
         dataBuffer->removeBytes(handled_len);
+        if(packet.type == Protocol::PacketType::SetTrigger) {
+            qDebug() << "Incoming set trigger from " << serial;
+        }
+        if(packet.type == Protocol::PacketType::ClearTrigger) {
+            qDebug() << "Incoming clear trigger from " << serial;
+        }
         switch(packet.type) {
         case Protocol::PacketType::Ack:
             emit receivedAnswer(TransmissionResult::Ack);
@@ -186,6 +192,12 @@ void LibreVNAUSBDriver::ReceivedData()
         case Protocol::PacketType::Nack:
             emit receivedAnswer(TransmissionResult::Nack);
             break;
+        case Protocol::PacketType::SetTrigger:
+            emit receivedTrigger(this, true);
+            break;
+        case Protocol::PacketType::ClearTrigger:
+            emit receivedTrigger(this, false);
+            break;
         case Protocol::PacketType::None:
             break;
         default:
diff --git a/Software/PC_Application/LibreVNA-GUI/appwindow.cpp b/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
index 1e4399d..57e6afa 100644
--- a/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
@@ -507,10 +507,13 @@ void AppWindow::CreateToolbars()
     tb_reference->addWidget(new QLabel("Ref out:"));
     toolbars.reference.outFreq = new QComboBox();
     tb_reference->addWidget(toolbars.reference.outFreq);
-    connect(toolbars.reference.type, qOverload<int>(&QComboBox::currentIndexChanged), this, &AppWindow::UpdateReference);
-    connect(toolbars.reference.outFreq, qOverload<int>(&QComboBox::currentIndexChanged), this, &AppWindow::UpdateReference);
+    connect(toolbars.reference.type, qOverload<int>(&QComboBox::currentIndexChanged), this, &AppWindow::ReferenceChanged);
+    connect(toolbars.reference.outFreq, qOverload<int>(&QComboBox::currentIndexChanged), this, &AppWindow::ReferenceChanged);
     addToolBar(tb_reference);
     tb_reference->setObjectName("Reference Toolbar");
+
+    referenceTimer.setSingleShot(true);
+    connect(&referenceTimer, &QTimer::timeout, this, &AppWindow::UpdateReference);
 }
 
 void AppWindow::SetupSCPI()
@@ -952,7 +955,7 @@ void AppWindow::ResetReference()
     toolbars.reference.outFreq->setCurrentIndex(0);
     toolbars.reference.type->blockSignals(false);
     toolbars.reference.outFreq->blockSignals(false);
-    UpdateReference();
+    ReferenceChanged();
 }
 
 //void AppWindow::StartManualControl()
@@ -1008,7 +1011,16 @@ void AppWindow::UpdateReferenceToolbar()
     }
     toolbars.reference.type->blockSignals(false);
     toolbars.reference.outFreq->blockSignals(false);
-    UpdateReference();
+    ReferenceChanged();
+}
+
+void AppWindow::ReferenceChanged()
+{
+    if(!device) {
+        // can't update without a device connected
+        return;
+    }
+    referenceTimer.start(100);
 }
 
 void AppWindow::UpdateReference()
diff --git a/Software/PC_Application/LibreVNA-GUI/appwindow.h b/Software/PC_Application/LibreVNA-GUI/appwindow.h
index 4a0469b..2d36579 100644
--- a/Software/PC_Application/LibreVNA-GUI/appwindow.h
+++ b/Software/PC_Application/LibreVNA-GUI/appwindow.h
@@ -82,6 +82,7 @@ private slots:
 //    void StartManualControl();
     void ResetReference();
     void UpdateReferenceToolbar();
+    void ReferenceChanged();
     void UpdateReference();
     void DeviceStatusUpdated();
     void DeviceFlagsUpdated();
@@ -144,6 +145,9 @@ private:
     QString deviceSerial;
     QActionGroup *deviceActionGroup;
 
+    // Reference change timer
+    QTimer referenceTimer;
+
     // Status bar widgets
     QLabel lConnectionStatus;
     QLabel lDeviceInfo;
diff --git a/Software/VNA_embedded/.settings/stm32cubeide.project.prefs b/Software/VNA_embedded/.settings/stm32cubeide.project.prefs
index 65c8f86..049399e 100644
--- a/Software/VNA_embedded/.settings/stm32cubeide.project.prefs
+++ b/Software/VNA_embedded/.settings/stm32cubeide.project.prefs
@@ -1,5 +1,5 @@
-2F62501ED4689FB349E356AB974DBE57=EF826FD321FB312AEADE4DB74B81458C
+2F62501ED4689FB349E356AB974DBE57=6F84FD31C089E822CF61FFCABCD0B7D1
 66BE74F758C12D739921AEA421D593D3=2
-8DF89ED150041C4CBC7CB9A9CAA90856=EF826FD321FB312AEADE4DB74B81458C
+8DF89ED150041C4CBC7CB9A9CAA90856=6F84FD31C089E822CF61FFCABCD0B7D1
 DC22A860405A8BF2F2C095E5B6529F12=BF78DB58F29884459C61AFB6BB93F7B6
 eclipse.preferences.version=1
diff --git a/Software/VNA_embedded/Application/VNA.cpp b/Software/VNA_embedded/Application/VNA.cpp
index c270852..01a05cc 100644
--- a/Software/VNA_embedded/Application/VNA.cpp
+++ b/Software/VNA_embedded/Application/VNA.cpp
@@ -146,6 +146,7 @@ bool VNA::Setup(Protocol::SweepSettings s) {
 	vTaskDelay(5);
 	data.clear();
 	HW::SetMode(HW::Mode::VNA);
+	Trigger::SetInput(false);
 
 	sourceRefIndex = 0;
 	LO1RefIndex = 0;