SSB demod: reworked AGC to handle the threshold gate properly

plugins/channelrx/demodssb/readme.md

@@ -2,7 +2,7 @@
 
 <h2>Introduction</h2>
 
-This plugin can be used to listen to a single sideband or double sidebands modulated signal. 
+This plugin can be used to listen to a single sideband or double sidebands modulated signal.
 
 <h2>Interface</h2>
 
@@ -24,7 +24,7 @@ Average total power in dB relative to a +/- 1.0 amplitude signal received in the
 
   - Monaural: the scalar signal is routed to both left and right audio channels
   - Binaural: the complex signal is fed with the real part on the left audio channel and the imaginary part to the right audio channel
-  
+
 <h3>4: Invert left and right channels</h3>
 
 Inverts left and right audio channels. Useful in binaural mode only.
@@ -91,7 +91,7 @@ This is how the Span (8) and bandpass (9, 10) filter controls look like in the 3
 Values are expressed in kHz and step is 100 Hz.
 
   - In SSB mode this is the upper (USB: positive frequencies) or lower (LSB: negative frequencies) cutoff of the in channel single side band bandpass filter. The value triggers LSB mode when negative and USB when positive
-  - In DSB mode this is half the bandwidth of the double side band in channel bandpass filter therefore the value is prefixed with the &#177; sign. 
+  - In DSB mode this is half the bandwidth of the double side band in channel bandpass filter therefore the value is prefixed with the &#177; sign.
 
 <h3>10: "Low cut": In channel bandpass filter cutoff frequency closest to zero</h3>
 
@@ -140,7 +140,7 @@ The signal power is calculated as the moving average over the AGC time constant
 
 Active only in AGC mode with squelch enabled.
 
-To avoid unwanted squelch opening on short transient bursts only signals with power above threshold during this period in milliseconds will open the squelch.It can be varied from 0 to 20 ms in 1 ms steps.
+To avoid unwanted squelch opening on short transient bursts only signals with power above threshold during this period in milliseconds will open the squelch.It can be varied from 0 to 20 ms in 1 ms steps then from 30 to 500 ms in 10 ms steps.
 
 When the power threshold is close to the noise floor a few milliseconds help in preventing noise power wiggle to open the squelch.
 

plugins/channelrx/demodssb/ssbdemodgui.cpp

@@ -202,9 +202,10 @@ void SSBDemodGUI::on_agcPowerThreshold_valueChanged(int value)
 
 void SSBDemodGUI::on_agcThresholdGate_valueChanged(int value)
 {
-    QString s = QString::number(value, 'f', 0);
+    int agcThresholdGate = value < 20 ? value : ((value - 20) * 10) + 20;
+    QString s = QString::number(agcThresholdGate, 'f', 0);
     ui->agcThresholdGateText->setText(s);
-    m_settings.m_agcThresholdGate = value;
+    m_settings.m_agcThresholdGate = agcThresholdGate;
     applySettings();
 }
 
@@ -565,10 +566,7 @@ void SSBDemodGUI::displaySettings()
 
     ui->agcPowerThreshold->setValue(m_settings.m_agcPowerThreshold);
     displayAGCPowerThreshold(ui->agcPowerThreshold->value());
-
-    ui->agcThresholdGate->setValue(m_settings.m_agcThresholdGate);
-    s = QString::number(ui->agcThresholdGate->value(), 'f', 0);
-    ui->agcThresholdGateText->setText(s);
+    displayAGCThresholdGate(m_settings.m_agcThresholdGate);
 
     blockApplySettings(false);
 }
@@ -586,6 +584,19 @@ void SSBDemodGUI::displayAGCPowerThreshold(int value)
     }
 }
 
+void SSBDemodGUI::displayAGCThresholdGate(int value)
+{
+    QString s = QString::number(value, 'f', 0);
+    ui->agcThresholdGateText->setText(s);
+    int dialValue = value;
+
+    if (value > 20) {
+        dialValue = ((value - 20) / 10) + 20;
+    }
+
+    ui->agcThresholdGate->setValue(dialValue);
+}
+
 void SSBDemodGUI::leaveEvent(QEvent*)
 {
 	m_channelMarker.setHighlighted(false);

plugins/channelrx/demodssb/ssbdemodgui.h

@@ -73,8 +73,8 @@ private:
 	void applyBandwidths(int spanLog2, bool force = false);
     int spanLog2Limit(int spanLog2);
 	void displaySettings();
-
 	void displayAGCPowerThreshold(int value);
+    void displayAGCThresholdGate(int value);
 
 	void leaveEvent(QEvent*);
 	void enterEvent(QEvent*);

plugins/channelrx/demodssb/ssbdemodgui.ui

@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>412</width>
+    <width>414</width>
     <height>190</height>
    </rect>
   </property>
@@ -18,7 +18,7 @@
   </property>
   <property name="minimumSize">
    <size>
-    <width>412</width>
+    <width>414</width>
     <height>0</height>
    </size>
   </property>
@@ -36,13 +36,13 @@
     <rect>
      <x>0</x>
      <y>0</y>
-     <width>410</width>
+     <width>415</width>
      <height>171</height>
     </rect>
    </property>
    <property name="minimumSize">
     <size>
-     <width>410</width>
+     <width>415</width>
      <height>0</height>
     </size>
    </property>
@@ -836,7 +836,7 @@
          <string>Power threshold gate (ms)</string>
         </property>
         <property name="maximum">
-         <number>20</number>
+         <number>68</number>
         </property>
         <property name="pageStep">
          <number>1</number>
@@ -850,7 +850,7 @@
        <widget class="QLabel" name="agcThresholdGateText">
         <property name="minimumSize">
          <size>
-          <width>16</width>
+          <width>22</width>
           <height>0</height>
          </size>
         </property>
@@ -858,7 +858,7 @@
          <string>Power threshold gate (ms)</string>
         </property>
         <property name="text">
-         <string>00</string>
+         <string>000</string>
         </property>
         <property name="alignment">
          <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>

plugins/channelrx/demodssb/ssbplugin.cpp

@@ -9,7 +9,7 @@
 
 const PluginDescriptor SSBPlugin::m_pluginDescriptor = {
 	QString("SSB Demodulator"),
-	QString("4.8.2"),
+	QString("4.10.0"),
 	QString("(c) Edouard Griffiths, F4EXB"),
 	QString("https://github.com/f4exb/sdrangel"),
 	true,