diff --git a/katdal/parquet_export.py b/katdal/parquet_export.py
new file mode 100644
index 00000000..ca754b90
--- /dev/null
+++ b/katdal/parquet_export.py
@@ -0,0 +1,133 @@
+import argparse
+from abc import ABC, abstractmethod
+import os.path
+import pickle
+import re
+import tempfile
+
+import numpy as np
+import numpy.typing as npt
+import pyarrow as pa
+import pyarrow.parquet as pq
+
+
+class EncodingStrategy(ABC):
+  @abstractmethod
+  def encode(self) -> pa.array:
+    raise NotImplementedError
+
+class BaseEncodingStrategy(EncodingStrategy):
+  def __init__(self, key: str, data: npt.NDArray):
+    self.key = key
+    self.data = data
+
+class NumericDataStrategy(BaseEncodingStrategy):
+  """ Encode numeric numpy arrays"""
+  def encode(self)  -> pa.array:
+    # Encode complex arrays as float arrays with an extra dimension
+    if np.iscomplexobj(self.data):
+      data = self.data.view(self.data.real.dtype).reshape(self.data.shape + (2,))
+    else:
+      data = self.data
+
+    if data.ndim > 1:
+      data = pa.FixedShapeTensorArray.from_numpy_ndarray(data)
+
+    return pa.array(data)
+
+class ObjectStrategy(BaseEncodingStrategy):
+  """ Encode object arrays, preferably as categoricals with pickled object values """
+  def encode(self) -> pa.array:
+    try:
+      values = {}
+      indices = []
+      for o in self.data:
+        indices.append(values.setdefault(o, len(values)))
+    except TypeError:
+      print(f"{self.key} not hashable, duplicates may be pickled")
+      return [pickle.dumps(o) for o in self.data]
+    else:
+      return pa.DictionaryArray.from_arrays(indices, [pickle.dumps(o) for o in values])
+
+class BpCalStrategy(BaseEncodingStrategy):
+  """ Encode large bpcal solution arrays by storing individual dump values as categorical raw bytes"""
+  def encode(self) -> pa.array:
+    try:
+      values = {}
+      indices = []
+      for o in self.data:
+        i, _ = values.setdefault(o.tobytes(), (len(values), o))
+        indices.append(i)
+    except TypeError:
+      return NumericDataStrategy(self.key, self.data).encode()
+    else:
+      dict_array = [pickle.dumps(o) for _, o in values.values()]
+      return pa.DictionaryArray.from_arrays(indices, dict_array)
+
+BPCAL_REGEX = re.compile(r"^.*cal_product_B.*$")
+KEY_STRATEGY = {BPCAL_REGEX: BpCalStrategy}
+
+def encoding_strategy(key: str, data: npt.NDArray) -> EncodingStrategy:
+  """ Return an encoding strategy dependent on the key and data"""
+  for regex, strategy_cls in KEY_STRATEGY.items():
+    if regex.match(key):
+      return strategy_cls(key, data)
+
+  if data.dtype == object:
+    return ObjectStrategy(key, data)
+
+  return NumericDataStrategy(key, data)
+
+def parquet_export(telstate, sensors):
+  """
+  Exports a katdal SensorCache to parquet as well as other smaller attrs.
+
+  Args:
+    telstate: katdal telstate
+    sensors: katdal SensorCache
+  """
+  IGNORED = {"sdisp_custom_signals"}
+
+  sensor_keys = (k for k in sensors.keys() if k not in IGNORED)
+  table_data = {k: encoding_strategy(k, sensors[k]).encode() for k in sensor_keys}
+  table = pa.Table.from_pydict(table_data)
+  cbid = telstate["capture_block_id"]
+  table_name = f"{tempfile.gettempdir()}{os.path.sep}telstate-{cbid}.parquet"
+  pq.write_table(table, table_name, row_group_size=10, compression="zstd")
+  print(f"Wrote to {table_name}")
+
+if __name__ == "__main__":
+  p = argparse.ArgumentParser()
+  p.add_argument("parquet")
+  args = p.parse_args()
+
+  # 1. Read the metadata from the file
+  parquet_file = pq.ParquetFile(args.parquet)
+  metadata = parquet_file.metadata
+
+  column_sizes = {}
+  total_file_size = 0
+
+  # 2. Iterate through all row groups
+  for i in range(metadata.num_row_groups):
+      row_group_meta = metadata.row_group(i)
+      total_file_size += row_group_meta.total_byte_size
+
+      # 3. Iterate through all column chunks in the row group
+      for j in range(row_group_meta.num_columns):
+          column_chunk_meta = row_group_meta.column(j)
+          column_name = column_chunk_meta.path_in_schema
+
+          # Use the compressed size for the file size contribution
+          current_sizes = column_sizes.setdefault(column_name, [0, 0])
+          current_sizes[0] += column_chunk_meta.total_uncompressed_size
+          current_sizes[1] += column_chunk_meta.total_compressed_size
+
+
+  # 4. Calculate relative size
+  print("Column | Compressed Size (Bytes) | Relative Size (%) | Uncompressed Size (Bytes) | Relative Size (%)")
+  print("-------|-------------------------|------------------------------------------------------------------")
+  for column, (full, compressed) in sorted(column_sizes.items(), key=lambda k: k[1][0], reverse=True):
+      full_relative = (full / total_file_size) * 100 if total_file_size > 0 else 0
+      compressed_relative = (compressed / total_file_size) * 100 if total_file_size > 0 else 0
+      print(f"{column:55s} | {compressed:12,} | {compressed_relative:6.2f} | {full:12,} | {full_relative:6.2f}")
\ No newline at end of file
diff --git a/katdal/spectral_window.py b/katdal/spectral_window.py
index 784eef9d..885f0868 100644
--- a/katdal/spectral_window.py
+++ b/katdal/spectral_window.py
@@ -79,6 +79,9 @@ def __init__(self, centre_freq, channel_width, num_chans, product=None,
         self._channel_freqs_lock = threading.Lock()
         self._channel_freqs = None
 
+    def __reduce__(self):
+        return (SpectralWindow, (self.centre_freq, self.channel_width, self.num_chans, self.product, self.sideband, self.band, self.bandwidth))
+
     @property
     def channel_freqs(self):
         with self._channel_freqs_lock:
diff --git a/katdal/visdatav4.py b/katdal/visdatav4.py
index fc446345..49b5dd3a 100644
--- a/katdal/visdatav4.py
+++ b/katdal/visdatav4.py
@@ -523,6 +523,11 @@ def _before(date):
                 self._corrected = VisFlagsWeights(corrected_vis, corrected_flags,
                                                   corrected_weights, unscaled_weights)
 
+
+
+        from .parquet_export import parquet_export
+        parquet_export(attrs, self.sensor)
+
         # Apply default selection and initialise all members that depend
         # on selection in the process
         self.select(spw=0, subarray=0, ants=obs_ants)