Use subband 300 as the default to produce XSTs for

tangostationcontrol/tangostationcontrol/configuration/schemas/xst.json

@@ -9,6 +9,7 @@
   "properties": {
     "subbands": {
       "type": "array",
+      "default": [300],
       "minItems": 0,
       "maxItems": 7,
       "items": {

tangostationcontrol/tangostationcontrol/devices/observation_field.py

@@ -279,7 +279,7 @@ class ObservationField(LOFARDevice):
                 dtype=numpy.uint32,
             )
         except AttributeError:
-            return numpy.array([], dtype=numpy.uint32)
+            return numpy.array([300], dtype=numpy.uint32)
 
     @attribute(
         doc="The subband indices are increased with this index every interval, causing different subbands to be emitted.",