no advanced civ is using hertz EM waves.
Hertz EM waves are only good for broadcasts and look at us, we already replacing broadcast TV with IPtv. If our phycisists would not be so blind and look into the predicted (Lord Kelvin) and discovered (Tesla) scalar waves and would try to understand how smith coils work, we would also not use Hertz EM waves for our point2point connections, which turn the spectrum into a unnecessary shared medium.
But that would require thinking outside the box...