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TDR.py
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# NanoVNASaver
#
# A python program to view and export Touchstone data from a NanoVNA
# Copyright (C) 2019, 2020 Rune B. Broberg
# Copyright (C) 2020, 2021 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
import numpy as np
# pylint: disable=import-error, no-name-in-module
from scipy.signal import convolve
from scipy.constants import speed_of_light
from PyQt6 import QtWidgets, QtCore, QtGui
from NanoVNASaver.Windows.Defaults import make_scrollable
logger = logging.getLogger(__name__)
CABLE_PARAMETERS = (
("Jelly filled (0.64)", 0.64),
("Polyethylene (0.66)", 0.66),
("PTFE (Teflon) (0.70)", 0.70),
("Pulp Insulation (0.72)", 0.72),
("Foam or Cellular PE (0.78)", 0.78),
("Semi-solid PE (SSPE) (0.84)", 0.84),
("Air (Helical spacers) (0.94)", 0.94),
# Lots of cable types added by Larry Goga, AE5CZ
("RG-6/U PE 75\N{OHM SIGN} (Belden 8215) (0.66)", 0.66),
("RG-6/U Foam 75\N{OHM SIGN} (Belden 9290) (0.81)", 0.81),
("RG-8/U PE 50\N{OHM SIGN} (Belden 8237) (0.66)", 0.66),
("RG-8/U Foam (Belden 8214) (0.78)", 0.78),
("RG-8/U (Belden 9913) (0.84)", 0.84),
# Next one added by EKZ, KC3KZ, from measurement of actual cable
("RG-8/U (Shireen RFC®400 Low Loss) (0.86)", 0.86),
("RG-8X (Belden 9258) (0.82)", 0.82),
# Next three added by EKZ, KC3KZ, from measurement of actual cable
('RG-8X (Wireman "Super 8" CQ106) (0.81)', 0.81),
('RG-8X (Wireman "MINI-8 Lo-Loss" CQ118) (0.82)', 0.82),
('RG-58 (Wireman "CQ 58 Lo-Loss Flex" CQ129FF) (0.79)', 0.79),
("RG-11/U 75\N{OHM SIGN} Foam HDPE (Belden 9292) (0.84)", 0.84),
("RG-58/U 52\N{OHM SIGN} PE (Belden 9201) (0.66)", 0.66),
("RG-58A/U 54\N{OHM SIGN} Foam (Belden 8219) (0.73)", 0.73),
("RG-59A/U PE 75\N{OHM SIGN} (Belden 8241) (0.66)", 0.66),
("RG-59A/U Foam 75\N{OHM SIGN} (Belden 8241F) (0.78)", 0.78),
("RG-174 PE (Belden 8216)(0.66)", 0.66),
("RG-174 Foam (Belden 7805R) (0.735)", 0.735),
("RG-213/U PE (Belden 8267) (0.66)", 0.66),
("RG316 (0.695)", 0.695),
("RG402 (0.695)", 0.695),
("LMR-240 (0.84)", 0.84),
("LMR-240UF (0.80)", 0.80),
("LMR-400 (0.85)", 0.85),
("LMR400UF (0.83)", 0.83),
("Davis Bury-FLEX (0.82)", 0.82),
)
class TDRWindow(QtWidgets.QWidget):
updated = QtCore.pyqtSignal()
def __init__(self, app: QtWidgets.QWidget):
super().__init__()
self.app = app
self.td = []
self.distance_axis = []
self.step_response_Z = []
self.setWindowTitle("TDR")
self.setWindowIcon(self.app.icon)
QtGui.QShortcut(QtCore.Qt.Key.Key_Escape, self, self.hide)
layout = QtWidgets.QFormLayout()
make_scrollable(self, layout)
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.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)
self.tdr_velocity_input = QtWidgets.QLineEdit()
self.tdr_velocity_input.setDisabled(True)
self.tdr_velocity_input.setText("0.66")
self.tdr_velocity_input.textChanged.connect(self.app.dataUpdated)
layout.addRow("Velocity factor", self.tdr_velocity_input)
self.tdr_result_label = QtWidgets.QLabel()
layout.addRow("Estimated cable length:", self.tdr_result_label)
layout.addRow(self.app.tdr_chart)
def updateTDR(self):
# TODO: Let the user select whether to use high or low resolution TDR?
FFT_POINTS = 2**14
if len(self.app.data.s11) < 2:
return
if self.tdr_velocity_dropdown.currentData() == -1:
self.tdr_velocity_input.setDisabled(False)
else:
self.tdr_velocity_input.setDisabled(True)
self.tdr_velocity_input.setText(
str(self.tdr_velocity_dropdown.currentData())
)
try:
v = float(self.tdr_velocity_input.text())
except ValueError:
return
step_size = self.app.data.s11[1].freq - self.app.data.s11[0].freq
if step_size == 0:
self.tdr_result_label.setText("")
logger.info("Cannot compute cable length at 0 span")
return
s11 = [complex(d.re, d.im) for d in self.app.data.s11]
window = np.blackman(len(self.app.data.s11))
windowed_s11 = window * s11
td = np.abs(np.fft.ifft(windowed_s11, FFT_POINTS))
step = np.ones(FFT_POINTS)
step_response = convolve(td, step)
self.step_response_Z = 50 * (1 + step_response) / (1 - step_response)
time_axis = np.linspace(0, 1 / step_size, FFT_POINTS)
self.distance_axis = time_axis * v * speed_of_light
# peak = np.max(td)
# We should check that this is an actual *peak*, and not just
# a vague maximum
index_peak = np.argmax(td)
cable_len = round(self.distance_axis[index_peak] / 2, 3)
feet = math.floor(cable_len / 0.3048)
inches = round(((cable_len / 0.3048) - feet) * 12, 1)
self.tdr_result_label.setText(f"{cable_len}m ({feet}ft {inches}in)")
self.app.tdr_result_label.setText(f"{cable_len}m")
self.td = list(td)
self.updated.emit()