diff --git a/NanoVNASaver/Chart.py b/NanoVNASaver/Chart.py
index f7e6752..2976217 100644
--- a/NanoVNASaver/Chart.py
+++ b/NanoVNASaver/Chart.py
@@ -764,11 +764,15 @@ class FrequencyChart(Chart):
         for i in range(len(data)):
             x = self.getXPosition(data[i])
             y = y_function(data[i])
+            if y is None:
+                continue
             if self.isPlotable(x, y):
                 qp.drawPoint(int(x), int(y))
             if self.drawLines and i > 0:
                 prevx = self.getXPosition(data[i - 1])
                 prevy = y_function(data[i - 1])
+                if prevy is None:
+                    continue
                 qp.setPen(line_pen)
                 if self.isPlotable(x, y) and self.isPlotable(prevx, prevy):
                     qp.drawLine(x, y, prevx, prevy)
@@ -795,7 +799,8 @@ class FrequencyChart(Chart):
                     self.drawMarker(x, y, qp, m.color, self.markers.index(m)+1)
 
     def isPlotable(self, x, y):
-        return self.leftMargin <= x <= self.leftMargin + self.chartWidth and \
+        return y is not None and x is not None and \
+               self.leftMargin <= x <= self.leftMargin + self.chartWidth and \
                self.topMargin <= y <= self.topMargin + self.chartHeight
 
     def getPlotable(self, x, y, distantx, distanty):
@@ -1569,6 +1574,8 @@ class LogMagChart(FrequencyChart):
             maxValue = -100
             for d in self.data:
                 logmag = self.logMag(d)
+                if math.isinf(logmag):
+                    continue
                 if logmag > maxValue:
                     maxValue = logmag
                 if logmag < minValue:
@@ -1577,6 +1584,8 @@ class LogMagChart(FrequencyChart):
                 if d.freq < self.fstart or d.freq > self.fstop:
                     continue
                 logmag = self.logMag(d)
+                if math.isinf(logmag):
+                    continue
                 if logmag > maxValue:
                     maxValue = logmag
                 if logmag < minValue:
@@ -1673,6 +1682,8 @@ class LogMagChart(FrequencyChart):
 
     def getYPosition(self, d: Datapoint) -> int:
         logMag = self.logMag(d)
+        if math.isinf(logMag):
+            return None
         return self.topMargin + round((self.maxValue - logMag) / self.span * self.chartHeight)
 
     def valueAtPosition(self, y) -> List[float]:
@@ -1946,29 +1957,37 @@ class CombinedLogMagChart(FrequencyChart):
             maxValue = 0
             for d in self.data11:
                 logmag = self.logMag(d)
+                if math.isinf(logmag):
+                    continue
                 if logmag > maxValue:
                     maxValue = logmag
                 if logmag < minValue:
                     minValue = logmag
             for d in self.data21:
                 logmag = self.logMag(d)
+                if math.isinf(logmag):
+                    continue
                 if logmag > maxValue:
                     maxValue = logmag
                 if logmag < minValue:
                     minValue = logmag
 
-            for d in self.reference11:  # Also check min/max for the reference sweep
+            for d in self.reference11:
                 if d.freq < self.fstart or d.freq > self.fstop:
                     continue
                 logmag = self.logMag(d)
+                if math.isinf(logmag):
+                    continue
                 if logmag > maxValue:
                     maxValue = logmag
                 if logmag < minValue:
                     minValue = logmag
-            for d in self.reference21:  # Also check min/max for the reference sweep
+            for d in self.reference21:
                 if d.freq < self.fstart or d.freq > self.fstop:
                     continue
                 logmag = self.logMag(d)
+                if math.isinf(logmag):
+                    continue
                 if logmag > maxValue:
                     maxValue = logmag
                 if logmag < minValue:
@@ -2096,6 +2115,8 @@ class CombinedLogMagChart(FrequencyChart):
 
     def getYPosition(self, d: Datapoint) -> int:
         logMag = self.logMag(d)
+        if math.isinf(logMag):
+            return None
         return self.topMargin + round((self.maxValue - logMag) / self.span * self.chartHeight)
 
     def valueAtPosition(self, y) -> List[float]:
diff --git a/NanoVNASaver/RFTools.py b/NanoVNASaver/RFTools.py
index b530dbd..cf22b07 100644
--- a/NanoVNASaver/RFTools.py
+++ b/NanoVNASaver/RFTools.py
@@ -45,7 +45,7 @@ def serial_to_parallel(z: complex) -> complex:
     if z.imag == 0:
         return complex(z_sq_sum / z.real, math.copysign(math.inf, z_sq_sum))
     if z.real == 0:
-        return complex(math.copysign(math.inf,z_sq_sum), z_sq_sum / z.real)
+        return complex(math.copysign(math.inf, z_sq_sum), z_sq_sum / z.real)
     return complex(z_sq_sum / z.real, z_sq_sum / z.imag)
 
 
@@ -112,7 +112,8 @@ class Datapoint(NamedTuple):
         mag = abs(self.z)
         if mag > 0:
             return 20 * math.log10(mag)
-        return 0
+        return -math.inf
+
 
     @property
     def vswr(self) -> float:
@@ -169,4 +170,4 @@ class RFTools:
 
     @staticmethod
     def parseFrequency(freq: str) -> int:
-        return parseFrequency(freq)
\ No newline at end of file
+        return parseFrequency(freq)