The highest measured frequencies of EM waves are Gamma-rays and are typically produced from the decay of atomic nuclei. The most powerful sources of gamma-rays (and usually the sources with the shortest wavelength) are caused by astronomical events.
Radio waves, on the other hand, have the lowest energies, longest wavelengths, and lowest frequencies of any type of EM radiation. In order from highest to lowest energy, the sections of the EM spectrum are named: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves.
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