code: def ref_frequency(self, context):
          
          num_chans = self._manager.spectral_window_table.getcol(MS.NUM_CHAN)
          ref_freqs = self._manager.spectral_window_table.getcol(MS.REF_FREQUENCY)
  
          data = np.hstack((np.repeat(rf, bs) for bs, rf in zip(num_chans, ref_freqs)))
          return data.reshape(context.shape).astype(context.dtype)
docs: Reference frequency data source