Fix frequency calculation at logscale sweeps (#701) (#705)

AUTHORS.rst

@@ -41,3 +41,4 @@ Contributors
 * sysjoint-tek <[email protected]>
 * Thomas de Lellis <[email protected]>
 * zstadler <[email protected]>
+* Peter Hackenberg <[email protected]>

src/NanoVNASaver/Settings/Sweep.py

@@ -18,7 +18,7 @@
 #  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 import logging
 from enum import Enum
-from math import log
+from math import exp, log
 from threading import Lock
 from typing import Iterator, NamedTuple
 
@@ -145,12 +145,12 @@ def check(self):
             raise ValueError(f"Illegal sweep settings: {self}")
 
     def _exp_factor(self, index: int) -> float:
-        return 1 - log(self.segments + 1 - index) / log(self.segments + 1)
+        return exp(log((self.start + self.span)/self.start) / self.segments * index)
 
     def get_index_range(self, index: int) -> tuple[int, int]:
         if self.properties.logarithmic:
-            start = round(self.start + self.span * self._exp_factor(index))
-            end = round(self.start + self.span * self._exp_factor(index + 1))
+            start = round(self.start * self._exp_factor(index))
+            end = round(self.start * self._exp_factor(index + 1))
         else:
             start = self.start + index * self.points * self.stepsize
             end = start + (self.points - 1) * self.stepsize
@@ -160,7 +160,7 @@ def get_index_range(self, index: int) -> tuple[int, int]:
     def get_frequencies(self) -> Iterator[int]:
         for i in range(self.segments):
             start, stop = self.get_index_range(i)
-            step = (stop - start) / self.points
+            step = (stop - start) / (self.points - 1)
             freq = start
             for _ in range(self.points):
                 yield round(freq)

tests/test_sweep.py

@@ -44,12 +44,12 @@ def test_sweep(self):
         self.assertEqual(sweep.get_index_range(1), (12429117, 21170817))
         data = list(sweep.get_frequencies())
         self.assertEqual(data[0], 3600000)
-        self.assertEqual(data[-1], 29913383)
+        self.assertEqual(data[-1], 29999934) # should be close to 30000000
         sweep = Sweep(segments=3, properties=Properties(logarithmic=True))
-        self.assertEqual(sweep.get_index_range(1), (9078495, 16800000))
+        self.assertEqual(sweep.get_index_range(1), (7298642, 14797272))
         data = list(sweep.get_frequencies())
         self.assertEqual(data[0], 3600000)
-        self.assertEqual(data[-1], 29869307)
+        self.assertEqual(data[-1], 30000000)
 
         sweep2 = sweep.copy()
         self.assertEqual(sweep, sweep2)