Update TDR.py

Allow user to select |Z|, VSWR, or S11
NanoVNA-Saver · Oct 18, 2024 · f43a869 · f43a869
1 parent 2ec8981
commit f43a869
Showing 1 changed file with 32 additions and 9 deletions.
diff --git a/src/NanoVNASaver/Windows/TDR.py b/src/NanoVNASaver/Windows/TDR.py
@@ -89,16 +89,28 @@ def __init__(self, app: QtWidgets.QWidget):
         layout = QtWidgets.QFormLayout()
         make_scrollable(self, layout)
 
+        dropdown_layout = QtWidgets.QHBoxLayout()
+
         self.tdr_velocity_dropdown = QtWidgets.QComboBox()
         for cable_name, velocity in CABLE_PARAMETERS:
             self.tdr_velocity_dropdown.addItem(cable_name, velocity)
-        self.tdr_velocity_dropdown.insertSeparator(
-            self.tdr_velocity_dropdown.count()
-        )
+        self.tdr_velocity_dropdown.insertSeparator(self.tdr_velocity_dropdown.count())
         self.tdr_velocity_dropdown.addItem("Custom", -1)
         self.tdr_velocity_dropdown.setCurrentIndex(1)  # Default to PE (0.66)
         self.tdr_velocity_dropdown.currentIndexChanged.connect(self.updateTDR)
-        layout.addRow(self.tdr_velocity_dropdown)
+
+        dropdown_layout.addWidget(self.tdr_velocity_dropdown)
+
+        self.format_dropdown = QtWidgets.QComboBox()
+        self.format_dropdown.addItem("|Z|")
+        self.format_dropdown.addItem("S11")
+        self.format_dropdown.addItem("VSWR")
+
+        self.format_dropdown.currentIndexChanged.connect(self.updateFormat)
+
+        dropdown_layout.addWidget(self.format_dropdown)
+
+        layout.addRow(dropdown_layout)
 
         self.tdr_velocity_input = QtWidgets.QLineEdit()
         self.tdr_velocity_input.setDisabled(True)
@@ -111,6 +123,10 @@ def __init__(self, app: QtWidgets.QWidget):
 
         layout.addRow(self.app.tdr_chart)
 
+    def updateFormat(self):
+        self.app.tdr_chart.resetDisplayLimits()
+        self.updateTDR()
+
     def updateTDR(self):
         # TODO: Let the user select whether to use high or low resolution TDR?
         FFT_POINTS = 2**14
@@ -138,24 +154,31 @@ def updateTDR(self):
             return
 
         s11 = [complex(d.re, d.im) for d in self.app.data.s11]
+
         s11 = np.array(s11)
         s11 = np.concatenate([s11, np.conj(s11[-1:0:-1])]) # Include negative frequencies
         s11 = np.fft.fftshift(s11)
 
         window = np.blackman(len(s11))
-        windowed_s11 = window * s11 # Now windowing eliminates higher frequencies while leaving low frequencies untouched
+        windowed_s11 = window * s11 #Now windowing eliminates higher frequencies while leaving low frequencies untouched
 
         pad_points = (FFT_POINTS - len(windowed_s11)) // 2
         windowed_s11 = np.pad(windowed_s11, [pad_points + 1, pad_points]) # Pad array to length FFT_POINTS
         windowed_s11 = np.fft.ifftshift(windowed_s11)
 
         td = np.fft.ifft(windowed_s11)
-
         step = np.ones(FFT_POINTS)
         step_response = convolve(td, step)
-
-        self.step_response_Z = np.abs(50 * (1 + step_response) / (1 - step_response)) #Can plot impedance in terms of real and imaginary too
-
+        # calculate step response based on the format that the user selected
+        TDR_format = self.format_dropdown.currentText();
+        step_Z = 50 * (1 + step_response) / (1 - step_response)
+        step_refl_coefficient = np.abs((step_Z - 50)/(step_Z + 50))
+        if TDR_format == "|Z|":
+            self.step_response_Z = np.abs(step_Z)
+        elif TDR_format == "S11":
+            self.step_response_Z = 20 * np.log10(step_refl_coefficient)
+        elif TDR_format == "VSWR":
+            self.step_response_Z = np.abs((1 + step_refl_coefficient)/(1 - step_refl_coefficient))
         time_axis = np.linspace(0, 1 / step_size, FFT_POINTS)
         self.distance_axis = time_axis * v * speed_of_light
         # peak = np.max(td)