MUF (Maximum Usable Frequency)

Maximum Usable Frequency (MUF) is the highest radio frequency that can be used for reliable communication between two points via the ionosphere, a layer of charged particles in the Earth’s atmosphere. It depends on the current ionization levels, which vary with time, sun activity, and weather. If a radio signal is transmitted at a frequency higher than the MUF, it will likely be reflected back to Earth or absorbed, making communication impossible. Operators choose frequencies below the MUF to ensure signals bounce effectively, enabling long-distance radio communication without loss.