diff --git a/astroquery/nrao/core.py b/astroquery/nrao/core.py
index 68e0bf37b6..d2574d4b73 100644
--- a/astroquery/nrao/core.py
+++ b/astroquery/nrao/core.py
@@ -40,7 +40,12 @@ def wrapper(*args, **kwargs):
         if telescope_config.upper() not in Nrao.telescope_config:
             raise ValueError("'telescope_config' must be one of {!s}"
                              .format(Nrao.telescope_config))
-        if obs_band.upper() not in Nrao.obs_bands:
+        if isinstance(obs_band, (list, tuple)):
+            for ob in obs_band:
+                if ob not in Nrao.obs_bands:
+                    raise ValueError("'obs_band' must be one of {!s}"
+                                     .format(Nrao.obs_bands))
+        elif obs_band not in Nrao.obs_bands:
             raise ValueError("'obs_band' must be one of {!s}"
                              .format(Nrao.obs_bands))
         if sub_array not in Nrao.subarrays and sub_array != 'all':
@@ -69,7 +74,7 @@ class NraoClass(QueryWithLogin):
     telescope_config = ['ALL', 'A', 'AB', 'BnA', 'B', 'BC', 'CnB', 'C',
                         'CD', 'DnC', 'D', 'DA']
 
-    obs_bands = ['ALL', '4', 'P', 'L', 'S', 'C', 'X', 'U', 'K', 'Ka', 'Q', 'W']
+    obs_bands = ['ALL', 'all', '4', 'P', 'L', 'S', 'C', 'X', 'U', 'K', 'Ka', 'Q', 'W']
 
     subarrays = ['ALL', 1, 2, 3, 4, 5]
 
@@ -167,6 +172,12 @@ def _args_to_payload(self, **kwargs):
         else:
             freq_str = ""
 
+        obs_bands = kwargs.get('obs_band', 'all')
+        if isinstance(obs_bands, six.string_types):
+            obs_bands = obs_bands.upper()
+        elif isinstance(obs_bands, (list,tuple)):
+            obs_bands = [x.upper() for x in obs_bands]
+
         request_payload = dict(
             QUERYTYPE=kwargs.get('querytype', "OBSSUMMARY"),
             PROTOCOL=kwargs.get('protocol',"VOTable-XML"),
@@ -195,7 +206,7 @@ def _args_to_payload(self, **kwargs):
             SRAD=str(
                 commons.parse_radius(kwargs.get('radius', "1.0m")).deg) + 'd',
             TELESCOPE_CONFIG=kwargs.get('telescope_config', 'all').upper(),
-            OBS_BANDS=kwargs.get('obs_band', 'all').upper(),
+            OBS_BANDS=obs_bands,
             SUBARRAY=kwargs.get('subarray', 'all').upper(),
             SOURCE_ID=kwargs.get('source_id', ''),
             SRC_SEARCH_TYPE='SIMBAD or NED',
@@ -332,12 +343,15 @@ def query_async(self,
 
         response.raise_for_status()
 
-        if not response.content:
+        # fail if response is entirely whitespace or if it is empty
+        if not response.content.strip():
             if cache:
                 last_pickle = self._last_query.hash()+".pickle"
                 cache_fn = os.path.join(self.cache_location, last_pickle)
                 os.remove(cache_fn)
             if retry > 0:
+                log.warning("Query resulted in an empty result.  Retrying {0}"
+                            " more times.".format(retry))
                 self.query_async(cache=cache, retry=retry-1, **kwargs)
             else:
                 raise ValueError("Query resulted in an empty result but "
@@ -351,6 +365,7 @@ def query_region_async(self, coordinates, radius=1 * u.deg,
                            end_date="", freq_low=None, freq_up=None,
                            telescope_config='all', obs_band='all',
                            querytype='OBSSUMMARY', sub_array='all',
+                           project_code=None,
                            protocol='VOTable-XML',
                            retry=False,
                            get_query_payload=False, cache=True):