diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index b1448800..db1e2db0 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -7,8 +7,9 @@ repos:
     -   id: end-of-file-fixer
     -   id: check-yaml
     -   id: check-added-large-files
--   repo: https://github.com/psf/black
-    rev: 23.7.0
+    -   id: check-toml
+-   repo: https://github.com/psf/black-pre-commit-mirror
+    rev: 23.9.1
     hooks:
     -   id: black
         args: ["--line-length", "120"] # Adjust the max line length value as needed.
diff --git a/examples/antenna_like_GSSI_1500_fs.in b/examples/antenna_like_GSSI_1500_fs.in
index ff6cdbb9..e880dbdd 100644
--- a/examples/antenna_like_GSSI_1500_fs.in
+++ b/examples/antenna_like_GSSI_1500_fs.in
@@ -8,4 +8,4 @@ from toolboxes.GPRAntennaModels.GSSI import antenna_like_GSSI_1500
 gssi_objects = antenna_like_GSSI_1500(0.125, 0.094, 0.100, resolution=0.001)
 for obj in gssi_objects:
     print(obj.__str__())
-#end_python:
\ No newline at end of file
+#end_python:
diff --git a/gprMax/cmds_multiuse.py b/gprMax/cmds_multiuse.py
index 7b56dcb6..20cebdc1 100644
--- a/gprMax/cmds_multiuse.py
+++ b/gprMax/cmds_multiuse.py
@@ -171,8 +171,8 @@ class ExcitationFile(UserObjectMulti):
             # Interpolate waveform values
             w.userfunc = interpolate.interp1d(waveformtime, singlewaveformvalues, **kwargs)
 
-            logger.info(self.grid_name(grid) +
-                f"User waveform {w.ID} created using {timestr} and, if "
+            logger.info(
+                self.grid_name(grid) + f"User waveform {w.ID} created using {timestr} and, if "
                 f"required, interpolation parameters (kind: {kwargs['kind']}, "
                 f"fill value: {kwargs['fill_value']})."
             )
@@ -837,9 +837,7 @@ class Rx(UserObjectMulti):
 
     def _do_rotate(self, grid):
         """Performs rotation."""
-        new_pt = (self.kwargs["p1"][0] + grid.dx, 
-                  self.kwargs["p1"][1] + grid.dy, 
-                  self.kwargs["p1"][2] + grid.dz)
+        new_pt = (self.kwargs["p1"][0] + grid.dx, self.kwargs["p1"][1] + grid.dy, self.kwargs["p1"][2] + grid.dz)
         pts = np.array([self.kwargs["p1"], new_pt])
         rot_pts = rotate_2point_object(pts, self.axis, self.angle, self.origin)
         self.kwargs["p1"] = tuple(rot_pts[0, :])
diff --git a/gprMax/fields_outputs.py b/gprMax/fields_outputs.py
index 15053a90..24b0b6fa 100644
--- a/gprMax/fields_outputs.py
+++ b/gprMax/fields_outputs.py
@@ -69,7 +69,8 @@ def write_hdf5_outputfile(outputfile, G):
 
     # Write meta data and data for any subgrids
     sg_rxs = [True for sg in G.subgrids if sg.rxs]
-    if sg_rxs:
+    sg_tls = [True for sg in G.subgrids if sg.transmissionlines]
+    if sg_rxs or sg_tls:
         for sg in G.subgrids:
             grp = f.create_group(f"/subgrids/{sg.name}")
             write_hd5_data(grp, sg, is_subgrid=True)
diff --git a/gprMax/model_build_run.py b/gprMax/model_build_run.py
index 2dfd1426..4ca40867 100644
--- a/gprMax/model_build_run.py
+++ b/gprMax/model_build_run.py
@@ -276,7 +276,8 @@ class ModelBuildRun:
 
         # Write output data to file if they are any receivers in any grids
         sg_rxs = [True for sg in self.G.subgrids if sg.rxs]
-        if self.G.rxs or sg_rxs:
+        sg_tls = [True for sg in self.G.subgrids if sg.transmissionlines]
+        if self.G.rxs or sg_rxs or self.G.transmissionlines or sg_tls:
             write_hdf5_outputfile(config.get_model_config().output_file_path_ext, self.G)
 
         # Write any snapshots to file for each grid
diff --git a/gprMax/pml.py b/gprMax/pml.py
index 6c6654e8..38032728 100644
--- a/gprMax/pml.py
+++ b/gprMax/pml.py
@@ -231,14 +231,13 @@ class PML:
         self.initialise_field_arrays()
 
     def check_kappamin(self):
-        """Checks that the sum of all kappamin values, i.e. when a multi-pole 
-            PML is used, is not less than one.
+        """Checks that the sum of all kappamin values, i.e. when a multi-pole
+        PML is used, is not less than one.
         """
 
         kappamin = sum(cfs.kappa.min for cfs in self.CFS)
         if kappamin < 1:
-            logger.exception(f"Sum of kappamin value(s) for PML is {kappamin} "
-                             "and must be greater than one.")
+            logger.exception(f"Sum of kappamin value(s) for PML is {kappamin} " "and must be greater than one.")
             raise ValueError
 
     def initialise_field_arrays(self):