diff --git a/CAL/CalibrationCommon/lib/datacontainers/holography_dataset.py b/CAL/CalibrationCommon/lib/datacontainers/holography_dataset.py
index 16a50dde8e9d4fb73bf4ccaabb919bf34dce9e60..cdc98748b1a1c5af2fdb8774aeb0a97c72784568 100644
--- a/CAL/CalibrationCommon/lib/datacontainers/holography_dataset.py
+++ b/CAL/CalibrationCommon/lib/datacontainers/holography_dataset.py
@@ -128,8 +128,9 @@ class HolographyDataset():
         for hbs, ho in list_of_hbs_ms_tuples:
             if station_name in hbs.target_station_names:
                 frequency = ho.frequency
-
+                frequency_string = str(frequency)
                 for beamlet in self.beamlets:
+                    beamlet_string = str(beamlet)
                     reference_station_names, cross_correlation =\
                         ho.ms_for_a_given_beamlet_number[beamlet].\
                         read_cross_correlation_time_flags_per_station_names(station_name,
@@ -141,10 +142,10 @@ class HolographyDataset():
                         if reference_station not in self.data:
                             self.data[reference_station] = dict()
 
-                        if frequency not in self.data[reference_station]:
-                            self.data[reference_station][frequency] = dict()
+                        if frequency_string not in self.data[reference_station]:
+                            self.data[reference_station][frequency_string] = dict()
 
-                        self.data[reference_station][frequency][beamlet] = \
+                        self.data[reference_station][frequency_string][beamlet_string] = \
                             cross_correlation[reference_station_index, :]
 
 
@@ -230,11 +231,14 @@ class HolographyDataset():
         self.ra_dec = dict()
         
         for frequency in self.frequencies:
+            frequency_string = str(frequency)
             if frequency not in self.ra_dec:
-                self.ra_dec[frequency] = dict()
+                self.ra_dec[frequency_string] = dict()
             for beamlet in self.beamlets:
-                self.ra_dec[frequency][beamlet] = \
-                    virtual_pointing[(frequency, beamlet)]
+                beamlet_string = str(beamlet)
+                self.ra_dec[frequency_string][beamlet_string] = numpy.array( \
+                    virtual_pointing[(frequency, beamlet)],
+                    dtype=coordinate_type)
 
 
         # reads the target station position and the coordinate of its axes
@@ -324,6 +328,7 @@ class HolographyDataset():
             result.antenna_field_position = f.attrs[HDS_ANTENNA_FIELD_POSITION].tolist()
             result.reference_stations = list(f[HDS_REFERENCE_STATION])
             result.frequencies = list(f[HDS_FREQUENCY])
+
             result.ra_dec = dict()
             result.data = dict()
             result.beamlets = [i for i in range(f[HDS_DATA].shape[2])]