The electromagnetic environment of an aircraft or missile has both natural and man-made sources of electromagnetic radiation. The natural environment consists of atmospheric disturbances, galactic and intergalactic sources and precipitation static. On the other hand, man-made sources of electromagnetic radiation consist of functional and incidental sources.
Functional sources include that equipment having the purpose to generate electromagnetic energy. Radio and radar systems are two such examples.
Alternatively, incidental sources generate
electromagnetic radiation unintentionally as a by-product of their normal
operation. Examples include computer clocks, power supplies, switches, gaseous
discharge devices, motor brushes and actuators.