than done because electromagnetic field the exist everywhere you find electric currents. they're invisible to the human eye. there are man made sources such as x-rays, tv antenna and cell phone towers. the radiation differs as well. cell phones use non identify onizing radiation. non ionizing radiation doesn't -- heat your food up to your head. at the observatory, the mountains surrounding this valley help create a natural barrier. but as technology keeps encroaching, it's harder and harder to maintain. >> they can be unintentional transmitters. your digital camera creates radio frequency interference. all of that being said, this is