To produce a steady radio wave, you would need to swing a magnet or a charged particle back and forth at a frequency of at least a few thousand times per second (in the kilohertz or megahertz range). The exact frequency required to produce a radio wave depends on the specific application and the wavelength of the desired radio signal.
In general, to produce a radio wave, a magnet or a charged particle (such as an electron) must be accelerated back and forth in a conducting wire or antenna. This acceleration creates a changing electric field, which in turn produces a changing magnetic field. The changing magnetic field then produces a changing electric field, and the process repeats, creating a self-sustaining electromagnetic wave.
The frequency of this wave, measured in hertz (Hz), corresponds to the number of times the magnet or charged particle oscillates back and forth per second. For example, a radio wave with a frequency of 100 megahertz (MHz) oscillates back and forth 100 million times per second.
It's worth noting that the exact mechanism for generating radio waves can vary depending on the technology and application. For example, in some radio systems, the radio waves are generated by a circuit that produces a rapidly changing electrical current, rather than by the acceleration of a magnet or charged particle.