# NanoVNASaver
#
# A python program to view and export Touchstone data from a NanoVNA
# Copyright (C) 2019, 2020 Rune B. Broberg
# Copyright (C) 2020 NanoVNA-Saver Authors
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
import logging
import math
from PyQt5 import QtWidgets
from NanoVNASaver.Analysis import Analysis
from NanoVNASaver.Formatting import format_frequency
logger = logging.getLogger(__name__)
class LowPassAnalysis(Analysis):
def __init__(self, app):
super().__init__(app)
self._widget = QtWidgets.QWidget()
layout = QtWidgets.QFormLayout()
self._widget.setLayout(layout)
layout.addRow(QtWidgets.QLabel("Low pass filter analysis"))
layout.addRow(
QtWidgets.QLabel(
f"Please place {self.app.markers[0].name}"
f" in the filter passband."))
self.result_label = QtWidgets.QLabel()
self.cutoff_label = QtWidgets.QLabel()
self.six_db_label = QtWidgets.QLabel()
self.sixty_db_label = QtWidgets.QLabel()
self.db_per_octave_label = QtWidgets.QLabel()
self.db_per_decade_label = QtWidgets.QLabel()
layout.addRow("Result:", self.result_label)
layout.addRow("Cutoff frequency:", self.cutoff_label)
layout.addRow("-6 dB point:", self.six_db_label)
layout.addRow("-60 dB point:", self.sixty_db_label)
layout.addRow("Roll-off:", self.db_per_octave_label)
layout.addRow("Roll-off:", self.db_per_decade_label)
def reset(self):
self.result_label.clear()
self.cutoff_label.clear()
self.six_db_label.clear()
self.sixty_db_label.clear()
self.db_per_octave_label.clear()
self.db_per_decade_label.clear()
def runAnalysis(self):
self.reset()
pass_band_location = self.app.markers[0].location
logger.debug("Pass band location: %d", pass_band_location)
if len(self.app.data21) == 0:
logger.debug("No data to analyse")
self.result_label.setText("No data to analyse.")
return
if pass_band_location < 0:
logger.debug("No location for %s",
self.app.markers[0].name)
self.result_label.setText(
f"Please place {self.app.markers[0].name} in the passband.")
return
pass_band_db = self.app.data21[pass_band_location].gain
logger.debug("Initial passband gain: %d", pass_band_db)
initial_cutoff_location = -1
for i in range(pass_band_location, len(self.app.data21)):
db = self.app.data21[i].gain
if (pass_band_db - db) > 3:
# We found a cutoff location
initial_cutoff_location = i
break
if initial_cutoff_location < 0:
self.result_label.setText("Cutoff location not found.")
return
initial_cutoff_frequency = self.app.data21[initial_cutoff_location].freq
logger.debug("Found initial cutoff frequency at %d", initial_cutoff_frequency)
peak_location = -1
peak_db = self.app.data21[initial_cutoff_location].gain
for i in range(0, initial_cutoff_location):
db = self.app.data21[i].gain
if db > peak_db:
peak_db = db
peak_location = i
logger.debug("Found peak of %f at %d", peak_db, self.app.data[peak_location].freq)
self.app.markers[0].setFrequency(str(self.app.data21[peak_location].freq))
self.app.markers[0].frequencyInput.setText(str(self.app.data21[peak_location].freq))
cutoff_location = -1
pass_band_db = peak_db
for i in range(peak_location, len(self.app.data21)):
db = self.app.data21[i].gain
if (pass_band_db - db) > 3:
# We found the cutoff location
cutoff_location = i
break
cutoff_frequency = self.app.data21[cutoff_location].freq
cutoff_gain = self.app.data21[cutoff_location].gain - pass_band_db
if cutoff_gain < -4:
logger.debug(
"Cutoff frequency found at %f dB"
" - insufficient data points for true -3 dB point.",
cutoff_gain)
logger.debug("Found true cutoff frequency at %d", cutoff_frequency)
self.cutoff_label.setText(
f"{format_frequency(cutoff_frequency)}"
f" ({round(cutoff_gain, 1)} dB)")
self.app.markers[1].setFrequency(str(cutoff_frequency))
self.app.markers[1].frequencyInput.setText(str(cutoff_frequency))
six_db_location = -1
for i in range(cutoff_location, len(self.app.data21)):
db = self.app.data21[i].gain
if (pass_band_db - db) > 6:
# We found 6dB location
six_db_location = i
break
if six_db_location < 0:
self.result_label.setText("6 dB location not found.")
return
six_db_cutoff_frequency = self.app.data21[six_db_location].freq
self.six_db_label.setText(
format_frequency(six_db_cutoff_frequency))
ten_db_location = -1
for i in range(cutoff_location, len(self.app.data21)):
db = self.app.data21[i].gain
if (pass_band_db - db) > 10:
# We found 6dB location
ten_db_location = i
break
twenty_db_location = -1
for i in range(cutoff_location, len(self.app.data21)):
db = self.app.data21[i].gain
if (pass_band_db - db) > 20:
# We found 6dB location
twenty_db_location = i
break
sixty_db_location = -1
for i in range(six_db_location, len(self.app.data21)):
db = self.app.data21[i].gain
if (pass_band_db - db) > 60:
# We found 60dB location! Wow.
sixty_db_location = i
break
if sixty_db_location > 0:
sixty_db_cutoff_frequency = self.app.data21[sixty_db_location].freq
self.sixty_db_label.setText(
format_frequency(sixty_db_cutoff_frequency))
elif ten_db_location != -1 and twenty_db_location != -1:
ten = self.app.data21[ten_db_location].freq
twenty = self.app.data21[twenty_db_location].freq
sixty_db_frequency = ten * \
10 ** (5 * (math.log10(twenty) - math.log10(ten)))
self.sixty_db_label.setText(
f"{format_frequency(sixty_db_frequency)} (derived)")
else:
self.sixty_db_label.setText("Not calculated")
if (ten_db_location > 0 and
twenty_db_location > 0 and
ten_db_location != twenty_db_location):
octave_attenuation, decade_attenuation = self.calculateRolloff(
ten_db_location, twenty_db_location)
self.db_per_octave_label.setText(
str(round(octave_attenuation, 3)) + " dB / octave")
self.db_per_decade_label.setText(
str(round(decade_attenuation, 3)) + " dB / decade")
else:
self.db_per_octave_label.setText("Not calculated")
self.db_per_decade_label.setText("Not calculated")
self.result_label.setText(
"Analysis complete (" + str(len(self.app.data)) + " points)")
