code: def __intermediate_hwmode(self, radio):
          
          protocol = radio['protocol']
          if protocol in ['802.11a', '802.11b', '802.11g']:
              # return 11a, 11b or 11g
              return protocol[4:]
          # determine hwmode depending on channel used
          if radio['channel'] is 0:
              # when using automatic channel selection, we need an
              # additional parameter to determine the frequency band
              return radio.get('hwmode')
          elif radio['channel'] <= 13:
              return '11g'
          else:
              return '11a'
docs: possible return values are: 11a, 11b, 11g