How does NASA communicate with spacecraft?
When a direct electrical current is applied to a wire the current flow builds an electromagnetic field around the wire. This field sends a wave outward from the wire. When the current is removed, the field collapses which again sends a wave. If the current is applied and removed over and over for a period of time, a series of waves is propagated at a discrete frequency. If the current changes polarity, or direction repeatedly, that could make waves, too. This phenomenon is the basis of electromagnetivity and basically describes how radio waves are created within transmitters.
Other kinds of electromagnetic radiation, including radio waves, are made by natural processes such as the nuclear reactions in a star.
What are radio waves?
How is data put on radio waves?
What is frequency?
Where does DS1 get its electricity?
What is energy?
How are frequency and wavelength related?
More about radio waves and electromagnetic radiation.
What's a circuit?
What is em radiation?
What makes EM radiation?