new_contents: from pylayers.simul.link import *
  
  DL=DLink(L=Layout('defstr.ini'))
  DL.fGHz=np.arange(2.41,2.43,0.01)
  DL.b=DL.b+1
  DL.Aa=Antenna(typ='Omni')
  DL.Ab=Antenna(typ='Omni')
  DL.eval() 
  dist_a_b = np.sqrt(np.sum((DL.a-DL.b)**2))
  
  if DL.R.los:
      ak0 = DL.H.ak[0]
      tk0 = DL.H.tk[0]
      assert tk0*0.3 == dist_a_b, 'invalid distance'
      lak0 = 20* np.log10(ak0)
      Friss= 20*np.log10(2.4)+20*np.log10(dist_a_b) + 32.4
      assert np.allclose(-lak0,Friss,0.1), 'issue in Friss'
subject: add test DLink