diff --git a/src/ria_toolkit_oss/annotations/annotation_transforms.py b/src/ria_toolkit_oss/annotations/annotation_transforms.py
index 822a75a..bb165b6 100644
--- a/src/ria_toolkit_oss/annotations/annotation_transforms.py
+++ b/src/ria_toolkit_oss/annotations/annotation_transforms.py
@@ -45,7 +45,14 @@ def is_annotation_contained(inner: Annotation, outer: Annotation) -> bool:
     outer_sample_stop = outer.sample_start + outer.sample_count
 
     if inner.sample_start > outer.sample_start and inner_sample_stop < outer_sample_stop:
-        if inner.freq_lower_edge > outer.freq_lower_edge and inner.freq_upper_edge < outer.freq_upper_edge:
+        if (
+            inner.freq_lower_edge is not None
+            and inner.freq_upper_edge is not None
+            and outer.freq_lower_edge is not None
+            and outer.freq_upper_edge is not None
+            and inner.freq_lower_edge > outer.freq_lower_edge
+            and inner.freq_upper_edge < outer.freq_upper_edge
+        ):
             return True
 
     return False
diff --git a/src/ria_toolkit_oss/data/annotation.py b/src/ria_toolkit_oss/data/annotation.py
index d565e17..fe55f97 100644
--- a/src/ria_toolkit_oss/data/annotation.py
+++ b/src/ria_toolkit_oss/data/annotation.py
@@ -17,10 +17,10 @@ class Annotation:
     :type sample_start: int
     :param sample_count: The index of the ending sample of the annotation, inclusive.
     :type sample_count: int
-    :param freq_lower_edge: The lower frequency of the annotation.
-    :type freq_lower_edge: float
-    :param freq_upper_edge: The upper frequency of the annotation.
-    :type freq_upper_edge: float
+    :param freq_lower_edge: The lower frequency of the annotation. Optional; None if not specified in source.
+    :type freq_lower_edge: float, optional
+    :param freq_upper_edge: The upper frequency of the annotation. Optional; None if not specified in source.
+    :type freq_upper_edge: float, optional
     :param label: The label that will be displayed with the bounding box in compatible viewers including IQEngine.
      Defaults to an emtpy string.
     :type label: str, optional
@@ -34,8 +34,8 @@ class Annotation:
         self,
         sample_start: int,
         sample_count: int,
-        freq_lower_edge: float,
-        freq_upper_edge: float,
+        freq_lower_edge: Optional[float] = None,
+        freq_upper_edge: Optional[float] = None,
         label: Optional[str] = "",
         comment: Optional[str] = "",
         detail: Optional[dict] = None,
@@ -43,8 +43,8 @@ class Annotation:
         """Initialize a new Annotation instance."""
         self.sample_start = int(sample_start)
         self.sample_count = int(sample_count)
-        self.freq_lower_edge = float(freq_lower_edge)
-        self.freq_upper_edge = float(freq_upper_edge)
+        self.freq_lower_edge = float(freq_lower_edge) if freq_lower_edge is not None else None
+        self.freq_upper_edge = float(freq_upper_edge) if freq_upper_edge is not None else None
         self.label = str(label)
         self.comment = str(comment)
 
@@ -62,6 +62,8 @@ class Annotation:
         :returns: True if valid, False if not.
         """
 
+        if self.freq_lower_edge is None or self.freq_upper_edge is None:
+            return self.sample_count > 0
         return self.sample_count > 0 and self.freq_lower_edge < self.freq_upper_edge
 
     def overlap(self, other):
@@ -73,6 +75,14 @@ class Annotation:
 
         :returns: The area of the overlap in samples*frequency, or 0 if they do not overlap."""
 
+        if (
+            self.freq_lower_edge is None
+            or self.freq_upper_edge is None
+            or other.freq_lower_edge is None
+            or other.freq_upper_edge is None
+        ):
+            return 0
+
         sample_overlap_start = max(self.sample_start, other.sample_start)
         sample_overlap_end = min(self.sample_start + self.sample_count, other.sample_start + other.sample_count)
 
@@ -91,6 +101,8 @@ class Annotation:
 
         :returns: sample length multiplied by bandwidth."""
 
+        if self.freq_lower_edge is None or self.freq_upper_edge is None:
+            return 0
         return self.sample_count * (self.freq_upper_edge - self.freq_lower_edge)
 
     def __eq__(self, other: Annotation) -> bool:
@@ -103,13 +115,16 @@ class Annotation:
 
         annotation_dict = {SigMFFile.START_INDEX_KEY: self.sample_start, SigMFFile.LENGTH_INDEX_KEY: self.sample_count}
 
-        annotation_dict["metadata"] = {
+        metadata = {
             SigMFFile.LABEL_KEY: self.label,
             SigMFFile.COMMENT_KEY: self.comment,
-            SigMFFile.FHI_KEY: self.freq_upper_edge,
-            SigMFFile.FLO_KEY: self.freq_lower_edge,
             "ria:detail": self.detail,
         }
+        if self.freq_upper_edge is not None:
+            metadata[SigMFFile.FHI_KEY] = self.freq_upper_edge
+        if self.freq_lower_edge is not None:
+            metadata[SigMFFile.FLO_KEY] = self.freq_lower_edge
+        annotation_dict["metadata"] = metadata
 
         if _is_jsonable(annotation_dict):
             return annotation_dict
diff --git a/src/ria_toolkit_oss/view/view_signal.py b/src/ria_toolkit_oss/view/view_signal.py
index 628bb0e..875df85 100644
--- a/src/ria_toolkit_oss/view/view_signal.py
+++ b/src/ria_toolkit_oss/view/view_signal.py
@@ -81,6 +81,8 @@ def view_annotations(
             return 0
 
     for annotation in sorted(annotations, key=_threshold_sort_key, reverse=True):
+        if annotation.freq_lower_edge is None or annotation.freq_upper_edge is None:
+            continue
         t_start = annotation.sample_start / sample_rate
         t_width = annotation.sample_count / sample_rate
         f_start = annotation.freq_lower_edge
diff --git a/src/ria_toolkit_oss_cli/ria_toolkit_oss/annotate.py b/src/ria_toolkit_oss_cli/ria_toolkit_oss/annotate.py
index 6477d40..b4c8a95 100644
--- a/src/ria_toolkit_oss_cli/ria_toolkit_oss/annotate.py
+++ b/src/ria_toolkit_oss_cli/ria_toolkit_oss/annotate.py
@@ -86,9 +86,7 @@ def save_recording_auto(recording, output_path, input_path, quiet=False, overwri
     input_path = Path(input_path)
     fmt = detect_input_format(input_path)
 
-    output_path = determine_output_path(
-        input_path=input_path, output_path=output_path, fmt=fmt, overwrite=overwrite
-    )
+    output_path = determine_output_path(input_path=input_path, output_path=output_path, fmt=fmt, overwrite=overwrite)
 
     if not quiet:
         if fmt == "sigmf":
@@ -258,7 +256,11 @@ def list(input, verbose):
             user_comment = ann.comment or ""
 
         # Basic info
-        freq_range = f"{format_frequency(ann.freq_lower_edge)} - {format_frequency(ann.freq_upper_edge)}"
+        freq_range = (
+            f"{format_frequency(ann.freq_lower_edge)} - {format_frequency(ann.freq_upper_edge)}"
+            if ann.freq_lower_edge is not None and ann.freq_upper_edge is not None
+            else "N/A"
+        )
         click.echo(
             f"  [{i}] Samples {format_sample_count(ann.sample_start)}-"
             f"{format_sample_count(ann.sample_start + ann.sample_count)}: {ann.label}"
@@ -502,8 +504,7 @@ def clear(input, output, overwrite, force, quiet):
     help="Annotation type",
 )
 @click.option(
-    "--sample-rate", type=float, default=None,
-    help="Sample rate in Hz (overrides metadata; required if not in file)"
+    "--sample-rate", type=float, default=None, help="Sample rate in Hz (overrides metadata; required if not in file)"
 )
 @click.option("--output", "-o", type=click.Path(), help="Output file path")
 @click.option("--overwrite", is_flag=True, help="Overwrite input file (non-SigMF only)")
@@ -617,8 +618,7 @@ def energy(
     help="Annotation type",
 )
 @click.option(
-    "--sample-rate", type=float, default=None,
-    help="Sample rate in Hz (overrides metadata; required if not in file)"
+    "--sample-rate", type=float, default=None, help="Sample rate in Hz (overrides metadata; required if not in file)"
 )
 @click.option("--output", "-o", type=click.Path(), help="Output file path")
 @click.option("--overwrite", is_flag=True, help="Overwrite input file (non-SigMF only)")
@@ -707,8 +707,7 @@ def cusum(input, label, min_duration, window_size, tolerance, annotation_type, s
 )
 @click.option("--channel", type=int, default=0, help="Channel index to annotate (default: 0)")
 @click.option(
-    "--sample-rate", type=float, default=None,
-    help="Sample rate in Hz (overrides metadata; required if not in file)"
+    "--sample-rate", type=float, default=None, help="Sample rate in Hz (overrides metadata; required if not in file)"
 )
 @click.option("--output", "-o", type=click.Path(), help="Output file path")
 @click.option("--overwrite", is_flag=True, help="Overwrite input file (non-SigMF only)")
@@ -787,8 +786,7 @@ def threshold(input, threshold, label, window_size, annotation_type, channel, sa
 @click.option("--noise-threshold-db", type=float, help="Noise floor threshold in dB (auto-estimated if not specified)")
 @click.option("--min-component-bw", type=float, default=50e3, help="Min component bandwidth in Hz")
 @click.option(
-    "--sample-rate", type=float, default=None,
-    help="Sample rate in Hz (overrides metadata; required if not in file)"
+    "--sample-rate", type=float, default=None, help="Sample rate in Hz (overrides metadata; required if not in file)"
 )
 @click.option("--output", "-o", type=click.Path(), help="Output file path")
 @click.option("--overwrite", is_flag=True, help="Overwrite input file (non-SigMF only)")
@@ -809,7 +807,8 @@ def _log_separate_start(quiet, recording, indices_list, nfft, noise_threshold_db
 
 
 def separate(
-        input, indices, nfft, noise_threshold_db, min_component_bw, sample_rate, output, overwrite, quiet, verbose):
+    input, indices, nfft, noise_threshold_db, min_component_bw, sample_rate, output, overwrite, quiet, verbose
+):
     """
     Auto-detect parallel frequency-offset signals and split into sub-bands.
 
@@ -883,7 +882,11 @@ def separate(
                 click.echo("\n  Details:")
                 for i in range(initial_count, final_count):
                     ann = recording.annotations[i]
-                    freq_range = f"{format_frequency(ann.freq_lower_edge)} - {format_frequency(ann.freq_upper_edge)}"
+                    freq_range = (
+                        f"{format_frequency(ann.freq_lower_edge)} - {format_frequency(ann.freq_upper_edge)}"
+                        if ann.freq_lower_edge is not None and ann.freq_upper_edge is not None
+                        else "N/A"
+                    )
                     click.echo(
                         f"    [{i}] samples {format_sample_count(ann.sample_start)}-"
                         f"{format_sample_count(ann.sample_start + ann.sample_count)}: {freq_range}"
diff --git a/tests/datatypes/test_annotation.py b/tests/datatypes/test_annotation.py
index 5dfdeb5..033ef6a 100644
--- a/tests/datatypes/test_annotation.py
+++ b/tests/datatypes/test_annotation.py
@@ -199,3 +199,44 @@ def test_annotation_to_sigmf_format_values():
     values = list(result.values())
     assert 50 in values or ann.sample_start in values
     assert 100 in values or ann.sample_count in values
+
+
+# ---------------------------------------------------------------------------
+# None freq-edge regression tests (SigMF optional fields)
+# ---------------------------------------------------------------------------
+
+
+def test_annotation_no_freq_edges():
+    ann = Annotation(sample_start=0, sample_count=10, label="burst")
+    assert ann.freq_lower_edge is None
+    assert ann.freq_upper_edge is None
+
+
+def test_annotation_is_valid_no_freq_edges():
+    ann = Annotation(sample_start=0, sample_count=10, label="burst")
+    assert ann.is_valid() is True
+
+    ann_zero = Annotation(sample_start=0, sample_count=0, label="burst")
+    assert ann_zero.is_valid() is False
+
+
+def test_annotation_overlap_none_edges_returns_zero():
+    ann1 = Annotation(sample_start=0, sample_count=10)
+    ann2 = Annotation(sample_start=0, sample_count=10, freq_lower_edge=0, freq_upper_edge=100)
+    assert ann1.overlap(ann2) == 0
+    assert ann2.overlap(ann1) == 0
+
+
+def test_annotation_area_none_edges_returns_zero():
+    ann = Annotation(sample_start=0, sample_count=10, label="burst")
+    assert ann.area() == 0
+
+
+def test_annotation_to_sigmf_omits_freq_keys_when_none():
+    from sigmf import SigMFFile
+
+    ann = Annotation(sample_start=0, sample_count=10, label="burst")
+    result = ann.to_sigmf_format()
+    metadata = result["metadata"]
+    assert SigMFFile.FLO_KEY not in metadata
+    assert SigMFFile.FHI_KEY not in metadata
diff --git a/tests/io/test_recording_io.py b/tests/io/test_recording_io.py
index 16383c2..81ff1cc 100644
--- a/tests/io/test_recording_io.py
+++ b/tests/io/test_recording_io.py
@@ -189,3 +189,21 @@ def test_sigmf_3(tmp_path):
         to_sigmf(recording=recording1, path=tmp_path, filename=filename.name)
     except IOError as e:
         assert str(e) == "File already exists"
+
+
+def test_sigmf_annotation_without_freq_edges(tmp_path):
+    # Regression: annotations that omit the optional SigMF freq edge fields must
+    # load without error; edges should be None and the annotation still valid.
+    ann = Annotation(sample_start=0, sample_count=5, label="burst")
+    recording1 = Recording(data=complex_data_1, metadata=sample_metadata, annotations=[ann])
+
+    filename = tmp_path / "test"
+    to_sigmf(recording=recording1, path=tmp_path, filename=filename.name, overwrite=True)
+    recording2 = from_sigmf(filename)
+
+    assert len(recording2.annotations) == 1
+    loaded = recording2.annotations[0]
+    assert loaded.freq_lower_edge is None
+    assert loaded.freq_upper_edge is None
+    assert loaded.is_valid() is True
+    assert loaded.label == "burst"