Natural radio frequency fields

Natural radio frequency electromagnetic fields occur on earth in the form of radio waves and microwaves from outer space. The sources of these fields are the sun, some distant objects in the cosmos (Source: Max Planck Institute for Radio Astronomy), and the so-called cosmic background radiation the remains of the big bang (Sources: ESA; Due to the low intensity of the incoming radiation, and the shielding effect of the earth's atmosphere, the strength of the natural radio frequency electromagnetic background radiation on the earth is very low. The intensity is several orders of magnitude below the emissions of radio frequency fields in our environment. To illustrate this, there exists a comparison that about 1% of the noise level of an empty TV channel (i.e., of a TV image showing only noise) is caused by the microwave background radiation (Source: DESY).

All-sky picture of the infant universe. The image reveals 13.77 billion year old temperature fluctuations (shown as color differences) in the cosmic background radiation
photo: NASA, lizcense: public domain, via Wikimedia Commons