Add the posibility of use an attenuator inline

with the S21 (CH1) input
original from
https://github.com/mihtjel/nanovna-saver/pull/145

NanoVNASaver/NanoVNASaver.py

@@ -44,6 +44,7 @@ from .SweepWorker import SweepWorker
 from .Settings import BandsModel
 from .Touchstone import Touchstone
 from .about import version as ver
+from NanoVNASaver.RFTools import corrAttData
 
 logger = logging.getLogger(__name__)
 
@@ -57,6 +58,7 @@ class NanoVNASaver(QtWidgets.QWidget):
 
     def __init__(self):
         super().__init__()
+        self.s21att = 0.0
         if getattr(sys, 'frozen', False):
             logger.debug("Running from pyinstaller bundle")
             self.icon = QtGui.QIcon(f"{sys._MEIPASS}/icon_48x48.png")  # pylint: disable=no-member
@@ -684,7 +686,11 @@ class NanoVNASaver(QtWidgets.QWidget):
     def saveData(self, data, data12, source=None):
         if self.dataLock.acquire(blocking=True):
             self.data = data
-            self.data21 = data12
+            if self.s21att > 0:
+                corData12 = corrAttData(data12, self.s21att)
+                self.data21 = corData12
+            else:
+                self.data21 = data12
         else:
             logger.error("Failed acquiring data lock while saving.")
         self.dataLock.release()

NanoVNASaver/RFTools.py

@@ -95,6 +95,7 @@ def parseFrequency(freq: str) -> int:
         return -1
 
 
+
 class Datapoint(NamedTuple):
     freq: int
     re: float
@@ -173,3 +174,21 @@ class RFTools:
     @staticmethod
     def parseFrequency(freq: str) -> int:
         return parseFrequency(freq)
+
+def corrAttData(data: Datapoint, att: float):                                   
+    """Correct the ratio for a given attenuation on s21 input"""
+
+    if att <= 0:
+        return data
+    else:
+        att = 10**(att/20)
+
+    ndata = []
+    for i in range(len(data)):
+        freq, re, im = data[i]
+        orig = complex(re, im)
+        corrected = orig * att
+        ndata.append(Datapoint(freq, corrected.real, corrected.imag))
+
+    return ndata
+

NanoVNASaver/Windows/SweepSettings.py

@@ -73,14 +73,22 @@ class SweepSettingsWindow(QtWidgets.QWidget):
                 "Averaging allows discarding outlying samples to get better averages."))
         settings_layout.addRow(
             QtWidgets.QLabel("Common values are 3/0, 5/2, 9/4 and 25/6."))
+        
+        self.s21att = QtWidgets.QLineEdit("0")
 
+        settings_layout.addRow(QtWidgets.QLabel(""))
+        settings_layout.addRow(QtWidgets.QLabel("Some times when you measure amplifiers you need to use an attenuator"))
+        settings_layout.addRow(QtWidgets.QLabel("in line with  the S21 input (CH1) here you can specify it."))
+
+        settings_layout.addRow("Attenuator in port CH1 (s21) in dB", self.s21att)
+        settings_layout.addRow(QtWidgets.QLabel("Common values with un-un are 16.9 (49:1 2450) 9.54 (9:1 450)"))
         self.continuous_sweep_radiobutton.toggled.connect(
             lambda: self.app.worker.setContinuousSweep(
                 self.continuous_sweep_radiobutton.isChecked()))
         self.averaged_sweep_radiobutton.toggled.connect(self.updateAveraging)
         self.averages.textEdited.connect(self.updateAveraging)
         self.truncates.textEdited.connect(self.updateAveraging)
-
+        self.s21att.textEdited.connect(self.setS21Attenuator)
         layout.addWidget(settings_box)
 
         band_sweep_box = QtWidgets.QGroupBox("Sweep band")
@@ -145,6 +153,22 @@ class SweepSettingsWindow(QtWidgets.QWidget):
             f"Sweep span: {RFTools.formatShortFrequency(start)}"
             f" to {RFTools.formatShortFrequency(stop)}")
 
+    def setS21Attenuator(self):
+        
+        try:
+            s21att = float(self.s21att.text())
+        except:
+            s21att = 0
+
+        if (s21att < 0):
+            logger.warning("Values for attenuator are absolute and with no minus sign, resetting.")
+            self.s21att.setText("0")
+        else:
+            logger.info("Setting an attenuator of %.2f dB inline with the CH1/S21 input", s21att)
+            self.app.s21att = s21att
+
+
+
     def setBandSweep(self):
         index_start = self.band_list.model().index(self.band_list.currentIndex(), 1)
         index_stop = self.band_list.model().index(self.band_list.currentIndex(), 2)