code: def set_freqsweep_ext(self, amplitude, sweep_low_end, sweep_high_end, offset=0.0, output_state=True):
          
  
          sweep_deviation = round(abs(sweep_low_end - sweep_high_end)/2.0,6)
          freq = sweep_low_end + sweep_deviation
          commands = ['TYPE 3', #set to sweep
                      'SFNC 5',  #external modulation
                      'FREQ {0}'.format(freq),
                      'SDEV {0}'.format(sweep_deviation),
                      'MODL 1'   #enable modulation
                      ]
          if freq > 4.05e9:
              commands.append('AMPH {0}'.format(amplitude)) #set rear RF doubler amplitude
              if offset > 0.0:
                  print('HIGH FREQUENCY OUTPUT IS AC ONLY')
              if output_state is True:
                  commands.append('ENBH 1') #enable output
              else:
                  commands.append('ENBH 0')
          elif freq < 62.5e6:
              commands.extend(['AMPL {0}'.format(amplitude), 'OFSL {0}'.format(offset)]) #set front BNC amplitude
              if output_state is True:
                  commands.append('ENBL 1') #enable output
              else:
                  commands.append('ENBL 0')
  
          command_string = '\n'.join(commands)
          print_string = '\n\t' + command_string.replace('\n', '\n\t')
          logging.info(print_string)
          self.instr.write(command_string)
docs: Sets the Stanford MW function generator to freq modulation with external modulation.
          freq is the carrier frequency in Hz.