diff --git a/gprMax/cmds_multiuse.py b/gprMax/cmds_multiuse.py
index b151cb9a..385f6f92 100644
--- a/gprMax/cmds_multiuse.py
+++ b/gprMax/cmds_multiuse.py
@@ -871,7 +871,7 @@ class Rx(UserObjectMulti):
 
         try:
             r.ID = self.kwargs["id"]
-            outputs = [self.kwargs["outputs"]]
+            outputs = list(self.kwargs["outputs"])
         except KeyError:
             # If no ID or outputs are specified, use default
             r.ID = f"{r.__class__.__name__}({str(r.xcoord)},{str(r.ycoord)},{str(r.zcoord)})"
diff --git a/setup.py b/setup.py
index 743af3c6..409a97bd 100644
--- a/setup.py
+++ b/setup.py
@@ -253,7 +253,7 @@ else:
     )
 
     # Parse long_description from README.rst file.
-    with open("README.rst", "r") as fd:
+    with open("README.rst", "r", encoding="utf-8") as fd:
         long_description = fd.read()
 
     setup(
diff --git a/toolboxes/AntennaPatterns/initial_save.py b/toolboxes/AntennaPatterns/initial_save.py
index 1c849ab4..7a7fe4cb 100644
--- a/toolboxes/AntennaPatterns/initial_save.py
+++ b/toolboxes/AntennaPatterns/initial_save.py
@@ -13,10 +13,15 @@ import h5py
 import matplotlib.pyplot as plt
 import numpy as np
 
-import gprMax.config as config
+from scipy.constants import c
+from scipy.constants import epsilon_0 as e0
+from scipy.constants import mu_0 as m0
+
 
 logger = logging.getLogger(__name__)
 
+# Impedance of free space (Ohms)
+z0 = np.sqrt(m0 / e0) 
 
 # Parse command line arguments
 parser = argparse.ArgumentParser(
@@ -59,9 +64,9 @@ traceno = np.s_[:]  # All traces
 # Critical angle and velocity
 if epsr:
     mr = 1
-    z1 = np.sqrt(mr / epsr) * config.sim_config.em_consts["z0"]
-    v1 = config.sim_config.em_consts["c"] / np.sqrt(epsr)
-    thetac = np.round(np.arcsin(v1 / config.sim_config.em_consts["c"]) * (180 / np.pi))
+    z1 = np.sqrt(mr / epsr) * z0
+    v1 = c / np.sqrt(epsr)
+    thetac = np.round(np.arcsin(v1 / c * (180 / np.pi))
     wavelength = v1 / f
 
 # Print some useful information
@@ -189,8 +194,8 @@ for radius in range(0, len(radii)):
             Ethetasum[index] = np.sum(Etheta[:, index] ** 2) / z1
             Hthetasum[index] = np.sum(Htheta[:, index] ** 2) / z1
         else:
-            Ethetasum[index] = np.sum(Etheta[:, index] ** 2) / config.sim_config.em_consts["z0"]
-            Hthetasum[index] = np.sum(Htheta[:, index] ** 2) / config.sim_config.em_consts["z0"]
+            Ethetasum[index] = np.sum(Etheta[:, index] ** 2) / z0
+            Hthetasum[index] = np.sum(Htheta[:, index] ** 2) / z0
 
         index += 1
 
diff --git a/toolboxes/AntennaPatterns/plot_fields.py b/toolboxes/AntennaPatterns/plot_fields.py
index d6f85e4b..b43160ed 100644
--- a/toolboxes/AntennaPatterns/plot_fields.py
+++ b/toolboxes/AntennaPatterns/plot_fields.py
@@ -12,11 +12,17 @@ import os
 import matplotlib.pyplot as plt
 import numpy as np
 
-import gprMax.config as config
+from scipy.constants import c
+from scipy.constants import epsilon_0 as e0
+from scipy.constants import mu_0 as m0
+
 
 logger = logging.getLogger(__name__)
 
 
+# Impedance of free space (Ohms)
+z0 = np.sqrt(m0 / e0)
+
 # Parse command line arguments
 parser = argparse.ArgumentParser(
     description="Plot field patterns from a simulation with receivers positioned in circles around an antenna. This module should be used after the field pattern data has been processed and stored using the initial_save.py module.",
@@ -56,9 +62,9 @@ step = 12
 # Critical angle and velocity
 if epsr:
     mr = 1
-    z1 = np.sqrt(mr / epsr) * config.sim_config.em_consts["z0"]
-    v1 = config.sim_config.em_consts["c"] / np.sqrt(epsr)
-    thetac = np.round(np.rad2deg(np.arcsin(v1 / config.sim_config.em_consts["c"])))
+    z1 = np.sqrt(mr / epsr) * z0
+    v1 = c / np.sqrt(epsr)
+    thetac = np.round(np.rad2deg(np.arcsin(v1 / c)))
     wavelength = v1 / f
 
 # Print some useful information