def ref_frequency(self, context):
        """ Reference frequency data source """
        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)
Reference frequency data source